JP2001211455A - Image coding method and image coder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image coder that can obtain high image quality uniform over the entire image without increasing the quantization step size, as in a conventional coder, even when the image with complicated pattern is consecutive. SOLUTION: First coded data are generated by applying predication coding, DC transform, quantization with a prescribed quantization step size and variable length coding to an input video signal. The assigned code quantity by each frame or each GOP is obtained on the basis of a data quantity and an available total data quantity by a prescribed time each of the 1st coded data e.g. by each frame and each GOP, the input video signal is coded by each prescribed time on the basis of the assigned code quantity to generate 2nd coded data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method, an image encoding device, and an image recording medium, and more particularly, to a method for encoding a video signal of a moving image on an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape. This is used in a system that records video data, a system that transmits a video signal of a moving image via a transmission path, and the like.

[0002]

2. Description of the Related Art Conventionally, a system for transmitting a video signal of a moving image to a remote place, such as a video conference system and a video telephone system, and a video signal of a moving image are recorded on an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape. In a system or the like for reproducing a video signal of a recorded moving image, in order to efficiently use a transmission path (or an image recording medium), a video signal is so-called utilizing a line correlation or a frame correlation of the video signal. High-efficiency coding is performed to reduce the redundancy in the space axis direction and the time axis direction and transmit only significant information, thereby improving transmission efficiency.

For example, in an encoding process in the spatial axis direction (hereinafter referred to as an intra-frame encoding process), as shown in FIG.
For example, a line correlation of a video signal is used.
Each image P constituting a moving image at 1, t2, t3,.
When trying to transmit C1, PC2, PC3 ...
The image data to be transmitted is, for example, 1 in the same scanning line.
Data compression is performed by two-dimensional encoding or by dividing an image into a plurality of blocks and two-dimensionally encoding the image data of each block, thereby improving transmission efficiency.

In the encoding process in the time axis direction (hereinafter referred to as inter-frame encoding process), for example, so-called predictive encoding is performed using inter-frame correlation of a video signal, that is, as shown in FIG. Matching image PCl and PC
2, image data PC1 which is a difference (a so-called prediction error) of the image data of each corresponding pixel between PC2 and PC3.
2, PC23..., And these image data PC1
2, data is compressed by transmitting the PC 23, and the transmission efficiency is improved.

[0005] Thus, the images PC1, PC2, PC3
The video signal can be transmitted with a much smaller data amount than when all the image data is transmitted.

In the above-described predictive coding in the inter-frame coding process, for example, motion compensation prediction is used for each macroblock in order to further increase the efficiency. That is, for example, when a person in the center of the screen moves, the movement of a moving object on the screen is detected, and the position of the image data used for prediction in the image preceding by the movement is corrected to perform the prediction. By performing the encoding, the encoding efficiency can be improved. However, even now, much data must be sent to the part where the object moves and appears from behind. Therefore, the coding efficiency can be further improved by performing the motion compensation prediction not only in the above-mentioned forward direction but also in the backward direction or in a combination of both.

Specifically, as shown in FIG. 8A, frame data F0, F1,... Of the 0th, 1st, 2nd, 3rd,...
In the macroblocks F2, F3,..., When there is a change in the image as represented by the motion vectors X0, X1, X2, X3,. Every second (for example, one frame), that is, the second, fourth,..., Frames are designated as interpolation frames.
As shown in B, transmission interpolation frame data F2X, F4X... Are generated by predetermined interpolation frame processing. In addition, the frame data F
, F3... Are subjected to a predetermined encoding process to generate transmission non-interpolated frame data F1X, F3X.

For example, motion-compensated frame data F
3 and the frame data F2, the difference SP2 (prediction error), the motion-compensated frame data F1 and the frame data F2
, The motion-compensated frame data F1, F2
Then, a difference SP4 between the frame data and the frame data F2 obtained by performing the interpolation process on No. 3 is obtained for each macroblock, and the difference between the macroblock SP1 of the frame data F2 and these differences is compared. And these data SP
1 to SP4, the data with the smallest data generation amount is referred to as transmission interpolation data F2X in macroblock units, and so on.
... is generated. Also, for example, the non-interpolated frame data F1, F3,... Are subjected to, for example, DCT conversion processing, variable-length coding processing, etc. to generate transmission non-interpolated frame data F1X, F3X.

The transmission non-interpolated frame data F1X, F3X...
.. Together with the data of the motion vectors X0, X1, X3,... As transmission data DATA to the device on the receiving side.

On the other hand, the apparatus on the receiving side transmits transmitted data DATA (transmitted non-interpolated frame data F1X, F3X
,..., Transmission interpolation data F2X, F4X,..., Motion vectors X0, X1, X3,. , F2, F3,... As a result, the coding efficiency can be further improved by performing the motion compensation prediction not only in the forward direction but also in the backward direction or in a combination of the two directions.

Here, an image encoding apparatus and an image decoding apparatus having the above-described functions will be described.

As shown in FIG. 9, the image encoding apparatus 60 includes a pre-processing circuit 61 for separating an input video signal VD into a luminance signal and a color difference signal, a luminance signal from the pre-processing circuit 61,
Analog / digital (hereinafter referred to as A / D) conversion circuits 62a and 62 for converting color difference signals into digital signals, respectively.
2b, a frame memory group 63 for storing luminance data and color difference data (hereinafter referred to as image data) from the A / D conversion circuits 62a and 62b, and a frame memory group 63
A format conversion circuit 64 for reading out image data from the format conversion circuit 64 in accordance with a block format, and an encoder 65 for encoding the image data of the block from the format conversion circuit 64 with high efficiency.

The pre-processing circuit 61 separates the input video signal VD into a luminance signal and a chrominance signal.
2a and 62b convert the luminance signal and the chrominance signal into 8-bit luminance data and chrominance data, respectively, and the frame memory group 63 stores these luminance data and chrominance data.

The format conversion circuit 64 converts the image data (luminance data,
Color difference data) according to a block format, and the encoder 65 encodes the read image data by predetermined high-efficiency encoding, and outputs a bit stream.

The bit stream is supplied to an image decoding device 80 via a transmission path or a transmission medium 70 including an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape.

As shown in FIG. 9 described above, the image decoding apparatus 80 includes a decoder 81 corresponding to the encoder 65.
A format conversion circuit 82 for converting the image data reproduced by the decoder 81 into a frame format,
A frame memory group 83 for storing image data from the format conversion circuit 82; D / A conversion circuits 84a and 84b for converting luminance data and color difference data read from the frame memory group 83 into analog signals; A post-processing circuit 85 that mixes the luminance signal and the color difference signals from the conversion circuits 84a and 84b to generate an output video signal.

The decoder 81 includes an encoder 65
The bit stream is decoded by decoding corresponding to the high-efficiency encoding to reproduce the image data in the block format, and the format conversion circuit 82 converts the image data into the frame format, and
3 is stored.

The D / A conversion circuits 84a and 84b convert the luminance data and chrominance data read from the frame memory group 83 into a luminance signal and a chrominance signal, respectively. The signals are mixed to generate an output video signal.

Specifically, the preprocessing circuit 61 and the A / D conversion circuits 62a and 62b convert the luminance signal and the color difference signal into digital signals as described above, The number of pixels is の of the luminance signal
After reducing the amount of data so that
The obtained luminance data and color difference data are stored in a frame memory group 6
Supply 3

The luminance data and the color difference data are read from the frame memory group 63 in accordance with the block format as described above. That is, for example, image data for one frame is divided into N slices as shown in FIG. 10A, and each slice includes M macroblocks as shown in FIG. As shown in FIG. 10C, the block is a block unit composed of 8 × 8 pixels, and luminance data Y1, Y2, Y3, and Y4 of four luminance blocks adjacent vertically, horizontally, and
The color difference data includes color difference data Cb and Cr of a color difference block composed of 8 × 8 pixels in a range corresponding to these four luminance blocks. Then, from the frame memory group 63, image data continues in units of macroblocks in the slice, and Y1, Y2, Y3, Y4, Cb, C
The luminance data and the color difference data are read so as to be continuous in the order of r. The image data read according to the block format in this manner is supplied to the encoder 65.

The encoder 65, as shown in FIG.
A motion vector detection circuit 101 is provided. The motion vector detection circuit 101 detects a motion vector of image data supplied in a block format on a macroblock basis. That is, the motion vector detection circuit 101 detects the motion vector of the current reference image in macroblock units using the front original image and / or the rear original image stored in the frame memory group 63. Here, in the detection of the motion vector, the motion vector in which the sum of the absolute values of the inter-frame differences in the macroblock unit is minimized is set as the motion vector. Then, the detected motion vector is supplied to the motion compensation circuit 113 and the like, and the sum of absolute values of the inter-frame differences in macroblock units is supplied to the intra-frame / forward / backward / bidirectional prediction determination circuit 103.

The intra / forward / backward / bidirectional prediction determination circuit 103 determines the prediction mode of the reference block based on this value, and, based on the determined prediction mode, the intra / forward prediction frame for each macroblock. The prediction encoding circuit 104 is controlled so as to switch between / backward / bidirectional prediction. Then, the predictive encoding circuit 104
a, 104b, 104c, and a changeover switch 104d. The input image data itself is used in the intra-frame coding mode, and the difference (pixel) of the input image data with respect to each prediction image in the forward / backward / bidirectional prediction mode. The data is supplied to the DCT circuit 105.

The DCT circuit 105 uses the two-dimensional correlation of the video signal to perform DCT on the input image data or difference data in block units and supplies the obtained coefficient data to the quantization circuit 106.

The quantization circuit 106 quantizes the coefficient data using a quantization step size (quantization scale) determined for each macroblock or slice, and encodes the obtained quantized data into a variable length code (VLC: Variable Length).
(Code) circuit 107 and an inverse quantization circuit 108. By the way, the quantization step size used for the quantization is determined by feeding back the remaining buffer amount of the transmission buffer memory 109, which will be described later, so that the transmission buffer memory 109 does not fail. The quantization step size is also determined by the VLC circuit. 107 and inverse quantization circuit 1
08.

The VLC circuit 107 performs variable length coding on the quantized data together with the quantization step size, the prediction mode, and the motion vector, and supplies the data to the transmission buffer memory 109 as transmission data.

The transmission buffer memory 109 stores the transmission data once, reads it out at a constant bit rate, smoothes the transmission data and outputs it as a bit stream, and outputs the bit stream according to the amount of residual data remaining in the memory. Then, the quantization control signal in macroblock units is fed back to the quantization circuit 106 to control the quantization step size. Thereby, the transmission buffer memory 109
Adjusts the amount of data generated as a bit stream and maintains an appropriate amount of data in the memory (a data amount that does not cause overflow or underflow). For example, when the remaining amount of data in the transmission buffer memory 109 increases to the allowable upper limit, the transmission buffer memory 1
In step 09, the data amount of the quantized data is reduced by increasing the quantization step size of the quantization circuit 106 by the quantization control signal. On the other hand, when the remaining amount of data in the transmission buffer memory 109 decreases to the permissible lower limit, the transmission buffer memory 109 reduces the quantization step size of the quantization circuit 106 by the quantization control signal, thereby obtaining the data of the quantized data. Increase volume.

As described above, the bit stream output from the buffer memory 109 is transmitted at a constant bit rate to the transmission path and the transmission medium 70 composed of an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape as described above. The image is supplied to the image decoding apparatus 80 via

On the other hand, the inverse quantization circuit 108 inversely quantizes the quantized data supplied from the quantization circuit 106, and coefficient data (quantization distortion is added thereto) corresponding to the output of the DCT circuit 105 described above. ) Is reproduced, and the coefficient data is subjected to inverse discrete cosine transform (hereinafter, IDCT: Inverse Discrete C).
osine transform).

The IDCT circuit 110 converts the coefficient data into an ID
CT conversion and reproduces image data corresponding to the input image data in the intra-frame encoding mode, and reproduces difference data corresponding to the output of the prediction encoding circuit 104 in the forward / backward / bidirectional prediction mode. 111.
In the forward / backward / bidirectional prediction mode, the addition circuit 111 is supplied with motion-compensated predicted image data from a motion compensation circuit 113 described later, and adds the motion-compensated predicted image data and difference data. By doing so, the image data corresponding to the input image data is reproduced.

The image data thus reproduced is stored in the frame memory 112. That is, the inverse quantization circuit 108 to the addition circuit 111 constitute a local decoding circuit, and the quantization circuit 1
The quantized data output from 06 is locally decoded, and the obtained decoded image is written to the frame memory 112 as a forward predicted image or a backward predicted image. Frame memory 1
Numeral 12 is composed of a plurality of frame memories, the bank switching of the frame memories is performed, and a single frame is output as forward prediction image data or backward prediction image data depending on the image to be encoded. . In the case of bidirectional prediction, forward predicted image data and backward predicted image data are averaged and output, for example. These predicted image data are exactly the same images as the images reproduced by the decoder 81 described later, and the next processed image is subjected to forward / backward / bidirectional prediction encoding based on this predicted image.

That is, the image data read from the frame memory 112 is supplied to the motion compensation circuit 113,
This motion compensation circuit 113 calculates
The motion compensation is performed on the prediction image data, and the motion compensated prediction image data is added to the prediction encoding circuit 104 and the addition circuit 111.
To supply.

Next, the decoder 81 will be described.

A bit stream is input to the decoder 81 via the transmission medium 70. This bit stream is input to a variable length decoding (hereinafter referred to as IVLC) circuit 202 via a reception buffer 201 as shown in FIG. The IVLC circuit 202 reproduces quantized data, a motion vector, a prediction mode, a quantization step size, and the like from the bit stream. These quantization data and quantization step size are supplied to the inverse quantization circuit 203,
The motion vector is supplied to the motion compensation circuit 207, and the prediction mode is supplied to the addition circuit 205.

The operations of the inverse quantization circuit 203 to the addition circuit 205 are the same as those of the local decoding circuit of the encoder 61, and the operations of the frame memory group 206 and the motion compensation circuit 207 are the frame memory 112 and the motion compensation circuit of the encoder 61, respectively. The decoding is performed based on the quantization data, the motion vector, the prediction mode, and the quantization step size. As a result, reproduced image data is output from the addition circuit 205.

As described above, in the conventional apparatus, the encoding bit rate of the bit stream generated by the encoder 65 is fixed in accordance with the transfer rate of the transmission medium 70, and under this restriction, the amount of data generation, that is, The quantization step size of the quantization circuit 106 in the encoder 65 has been controlled. In other words, for example, when images with complicated patterns continue, the quantization step size is increased to suppress the amount of data generation, and conversely, when simple patterns continue, the quantization step size is reduced to reduce the data size. By increasing the generation amount, a fixed rate is maintained without causing an overflow or underflow of the buffer memory 109.

Therefore, in the conventional apparatus, when a complicated image is continuous, the quantization step size is increased,
When the image quality is degraded and simple images continue, the quantization step size is reduced, and it is not possible to obtain uniform image quality throughout.

When a bit stream is recorded on an image recording medium having a limited data capacity, in order to prevent an extreme deterioration in image quality of an image having a complicated pattern, the image quality of the complicated image is not impaired. A higher fixed rate must be applied to the whole, resulting in reduced recording time.

[0038]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method, for example, in which images having complicated patterns It is an object of the present invention to provide an image encoding method, an image encoding device, and an image recording medium capable of obtaining uniform high image quality throughout without increasing the quantization step size unlike the conventional device.

Another object of the present invention is to make it possible to effectively use a limited recording capacity when recording on an image recording medium, to increase the recording time of image data on the image recording medium, Another object of the present invention is to provide an image encoding method, an image encoding device, and an image recording medium that can reproduce uniform high-quality image data from the entire image recording medium.

[0040]

In order to solve the above-mentioned problems, a first image encoding method according to the present invention encodes at least a part of an input video signal to generate first encoded data. Then, an encoding rate for each predetermined time is obtained based on the data amount of the first encoded data for each predetermined time and the total amount of usable data, and the input video signal is encoded for each predetermined time based on the encoding rate. To generate the second encoded data.

According to a second image encoding method of the present invention, in the first image encoding method, at least a part of the input video signal is quantized with a fixed quantization step size to obtain a first image encoding signal.
Is generated.

According to a third image encoding method of the present invention, in the first image encoding method, the total amount of usable data is proportionally distributed according to the amount of data for each predetermined time, and the code for each predetermined time is assigned. It is characterized by obtaining a conversion rate.

According to a fourth image encoding method of the present invention, a predetermined predictive encoding and / or
Alternatively, the first coefficient data is generated by performing a predetermined transform coding, the first coefficient data is quantized with a fixed quantization step size to generate first quantized data, and the first quantized data is generated. Is subjected to variable-length coding to generate a first bit stream, a coding rate for each predetermined time is determined based on the data amount of the first bit stream and the total amount of usable data, and a predetermined prediction code is input to the input video signal. And / or predetermined transform coding to generate second coefficient data, and quantizes the second coefficient data at a quantization step size based on a coding rate for each predetermined time to perform second quantization. Data is generated, and the second quantized data is variable-length coded to generate a second bit stream.

A fifth image encoding method according to the present invention is the video image encoding method according to the fourth image encoding method, wherein each frame in the first bit stream is based on the amount of data per frame and the total amount of usable data. The encoding rate is obtained.

A sixth image encoding method according to the present invention is the video image encoding method according to the fourth image encoding method, wherein at least a part of the data amount and usable data of each GOP including a plurality of frames in the first bit stream is used. GOP based on total data
It is characterized in that the coding rate is obtained every time.

According to a seventh image encoding method of the present invention, in the sixth image encoding method, the code for each GOP is determined based on the amount of data for the intra-coded image and the forward prediction coded image in the GOP. It is characterized by obtaining a conversion rate.

In an eighth image encoding method according to the present invention, in the fourth image encoding method, the total amount of usable data is proportionally distributed according to the amount of data of the first bit stream every predetermined time. , A coding rate for each predetermined time is obtained.

In a ninth image encoding method according to the present invention, a difficulty level of encoding is determined for each predetermined image unit of an input video signal, and a predetermined level is determined based on the difficulty level of encoding and the total amount of usable data. A coding rate is set for each image unit, and coding is performed on an input video signal such that the coding rate for each image unit matches the set coding rate for each image unit. .

A tenth image encoding method according to the present invention comprises:
In the ninth image encoding method, the predetermined image unit is a frame.

An eleventh image encoding method according to the present invention comprises:
In the ninth image encoding method, the predetermined image unit is a GOP including a plurality of frames.

A twelfth image encoding method according to the present invention comprises:
In the ninth image encoding method, at least a part of an input video signal is subjected to predetermined predictive coding and / or predetermined transform coding to generate coefficient data, and the coefficient data is quantized at a predetermined quantization step size. It is characterized in that the degree of difficulty of encoding is obtained by performing the conversion.

A first image encoding apparatus according to the present invention comprises: first encoding means for encoding at least a part of an input video signal to generate first encoded data; and first encoding means. Encoding control means for obtaining an encoding rate for each predetermined time based on a data amount of the first encoded data from the first time and a total amount of usable data, and a code for every predetermined time from the encoding control means. And a second encoding unit that encodes the input video signal at predetermined time intervals based on the encoding rate to generate second encoded data.

A second image encoding apparatus according to the present invention is the first image encoding apparatus, wherein the first encoding means quantizes at least a part of the input video signal with a fixed quantization step size. It is characterized in that it comprises a quantizing means for performing the following.

A third image encoding apparatus according to the present invention is the first image encoding apparatus, wherein the encoding control means distributes the total amount of usable data in proportion to the amount of data at predetermined time intervals. , A coding rate for each predetermined time is obtained.

The fourth image coding apparatus according to the present invention is configured such that a predetermined predictive coding and / or
Alternatively, a first encoding unit that performs predetermined transformation encoding to generate first coefficient data, and a first encoding unit that outputs the first coefficient data from the first encoding unit.
A first quantizing means for quantizing the coefficient data of the above with a fixed quantization step size to generate first quantized data;
A first variable-length encoding unit that performs variable-length encoding on the quantized data from the first quantization unit to generate a first bit stream; and a first bit stream from the first variable-length encoding unit. Coding control means for obtaining a coding rate for each predetermined time based on the amount of data and the total amount of data that can be used; and performing a predetermined predictive coding and / or a predetermined transform coding on an input video signal to obtain a second A second encoding unit for generating coefficient data, and quantizing the second coefficient data from the second encoding unit with a quantization step size based on an encoding rate for each predetermined time from the encoding control unit. A second quantizer for generating the second quantized data by using the second quantizer, and a second quantizer that performs variable-length encoding on the second quantized data from the second quantizer.
And a second variable-length encoding unit that generates a bit stream of

A fifth image encoding apparatus according to the present invention is the fourth image encoding apparatus, wherein the encoding control means is the first image encoding apparatus.
The coding rate is obtained for each frame based on the data amount of each frame and the total amount of usable data in the bit stream of (1).

A sixth image encoding device according to the present invention is the fourth image encoding device, wherein the encoding control means is the first image encoding device.
GOP consisting of multiple frames in the bit stream of
It is characterized in that the coding rate is obtained for each GOP based on at least a part of the data amount for each GOP and the total amount of usable data.

A seventh image encoding device according to the present invention is the sixth image encoding device, wherein the encoding control means is
The encoding rate for each GOP is obtained based on the data amount of the intra-coded image and the forward prediction coded image in P.

An eighth image encoding apparatus according to the present invention is the fourth image encoding apparatus, wherein the encoding control means reduces the total amount of usable data to the amount of data of the first bit stream every predetermined time. It is characterized in that the coding rate is determined every predetermined time by proportionally distributing the coding rate accordingly.

A ninth image encoding apparatus according to the present invention comprises: a difficulty calculating means for calculating a coding difficulty for each predetermined image unit of an input video signal; and a coding difficulty from the difficulty calculating means. Coding rate setting means for setting a coding rate for each predetermined image unit based on the total amount of data that can be used,
Encoding means for encoding the input video signal so that the encoding rate of each image unit matches the encoding rate of each image unit set by the encoding rate setting means. I do.

A tenth image encoding apparatus according to the present invention comprises:
In a ninth image encoding apparatus, the difficulty level calculating means obtains the encoding level for each frame.

An eleventh image encoding apparatus according to the present invention comprises:
In the ninth image encoding apparatus, the difficulty level calculating unit obtains the level of encoding difficulty for each GOP including a plurality of frames.

A twelfth image encoding apparatus according to the present invention comprises:
In the ninth image encoding device, the difficulty level calculating means includes a predetermined predictive encoding and / or
Alternatively, it is characterized in that coefficient data is generated by performing a predetermined transform coding, and the degree of coding difficulty is obtained by quantizing the coefficient data with a fixed quantization step size.

The first image recording medium according to the present invention encodes at least a part of an input video signal to generate first encoded data, and generates a first encoded data at a predetermined time interval. A coding rate for each predetermined time is obtained based on the total amount of usable data, and a second bit stream obtained by coding an input video signal every predetermined time based on the coding rate is recorded. And

In the second image recording medium according to the present invention, at least a part of the input video signal is subjected to predetermined predictive coding and / or predetermined transform coding to generate first coefficient data, Is quantized at a constant quantization step size to generate first quantized data, and the first quantized data is variable-length coded to generate a first bit stream, and a first bit stream is generated. A coding rate for each predetermined time is obtained based on the amount of data and the total amount of data that can be used, and predetermined coefficient coding and / or predetermined conversion coding are performed on the input video signal to generate second coefficient data. A second quantized data is generated by quantizing the second coefficient data with a quantization step size based on a coding rate for each predetermined time, and a second quantized data obtained by performing variable length encoding on the second quantized data is obtained. Bitstream of 2 Beam is characterized by comprising recorded.

In the third image recording medium according to the present invention, the difficulty of encoding is determined for each predetermined image unit of the input video signal,
An encoding rate is set for each predetermined image unit based on the degree of difficulty of encoding and the total amount of data that can be used, and the encoding rate for each image unit matches the set encoding rate for each image unit. In which encoded data obtained by encoding an input video signal is recorded.

In the first image encoding method according to the present invention, the data amount of the first encoded data obtained by encoding at least a part of the input video signal at every predetermined time and the total available data amount , An encoding rate for each predetermined time is obtained, and the input video signal is encoded every predetermined time based on the encoding rate to generate second encoded data.

In the second image encoding method according to the present invention,
In the first image encoding method, first encoded data is generated by quantizing at least a part of an input video signal with a fixed quantization step size, and an encoding rate is obtained. And encodes the input video signal at predetermined time intervals to generate second encoded data.

In the third image encoding method according to the present invention,
In the first image encoding method, the total amount of usable data is proportionally distributed according to the amount of data for each predetermined time to determine an encoding rate for each predetermined time, and the encoding rate is determined for each predetermined time based on the encoding rate. An input video signal is encoded to generate second encoded data.

In the fourth image encoding method according to the present invention,
A first bit stream is generated by subjecting at least a part of the input video signal to a predetermined predictive coding and / or a predetermined transform coding process, a quantization process at a fixed quantization step size, and a variable length coding process. The coding rate for each predetermined time is obtained based on the data amount of the first bit stream and the total amount of usable data. Then, a predetermined predictive encoding and / or a predetermined transform encoding process is performed on the input video signal,
Quantization processing at a quantization step size based on the encoding rate for each predetermined time and variable-length encoding
Generate a bitstream of.

In the fifth image encoding method according to the present invention,
In the fourth image encoding method, an encoding rate is determined for each frame based on the data amount of each frame in the first bit stream and the total amount of usable data. The input video signal is subjected to a predetermined predictive coding and / or a predetermined transform coding process, a quantization process at a quantization step size based on a coding rate for each frame, and a variable length coding process. 2 bit streams are generated.

In the sixth image encoding method according to the present invention,
In the fourth image encoding method, GO is determined based on at least a part of the data amount and the total available data amount for each GOP including a plurality of frames in the first bit stream.
An encoding rate is obtained for each P. Then, a predetermined predictive coding and / or a predetermined transform coding process is performed on the input video signal,
A second bit stream is generated by performing a quantization process at a quantization step size based on the coding rate for each OP and a variable length coding process.

In the seventh image encoding method according to the present invention,
In the sixth image coding method, a coding rate for each GOP is obtained based on the data amount of the intra-coded image and the forward prediction coded image in the GOP. The input video signal is subjected to predetermined predictive coding and / or predetermined transform coding processing, quantization processing at a quantization step size based on the coding rate for each GOP, and variable length coding processing. Generate a bitstream of.

In the eighth image encoding method according to the present invention,
In the fourth image encoding method, the total amount of usable data is proportionally distributed according to the amount of data of the first bit stream for each predetermined time, and an encoding rate for each predetermined time is obtained. Then, the input video signal is subjected to predetermined predictive coding and / or predetermined transform coding processing, quantization processing at a quantization step size based on a coding rate at predetermined time intervals, and variable length coding processing, and 2 bit streams are generated.

In the ninth image encoding method according to the present invention,
The encoding difficulty is determined for each predetermined image unit of the input video signal, and the encoding rate is set for each predetermined image unit based on the encoding difficulty and the total amount of usable data. Then, the input video signal is encoded such that the encoding rate of each image unit matches the set encoding rate of each image unit.

In a tenth image encoding method according to the present invention, in the ninth image encoding method, the difficulty of encoding is determined for each frame of the input video signal, and the encoding rate is determined for each frame. Then, the input video signal is encoded such that the encoding rate of each frame matches the set encoding rate of each frame.

According to an eleventh image encoding method according to the present invention, in the ninth image encoding method, the G
The encoding difficulty is determined for each OP, and the encoding rate is determined for each GOP. Then, the input video signal is encoded such that the encoding rate of each GOP matches the set encoding rate of each GOP.

In a twelfth image encoding method according to the present invention, in the ninth image encoding method, at least a part of the input video signal is obtained by performing predetermined predictive coding and / or predetermined transform coding. The difficulty of encoding is obtained by quantizing the coefficient data to be obtained with a fixed quantization step size. Then, the input video signal is encoded such that the encoding rate of each image unit matches the set encoding rate of each image unit.

In the first image coding apparatus according to the present invention,
A coding rate for each predetermined time is obtained based on a data amount for each predetermined time of the first encoded data obtained by encoding at least a part of the input video signal and a total amount of usable data. The input video signal is encoded at predetermined time intervals on the basis of the generated second encoded data.

In the second image encoding device according to the present invention,
In the first image encoding device, first encoded data is generated by quantizing at least a part of the input video signal with a constant quantization step size, and an encoding rate is obtained. And encodes the input video signal at predetermined time intervals to generate second encoded data.

In the third image encoding device according to the present invention,
In the first image encoding device, the total amount of usable data is proportionally distributed according to the amount of data for each predetermined time to determine an encoding rate for each predetermined time, and the encoding rate is determined for each predetermined time based on the encoding rate. An input video signal is encoded to generate second encoded data.

In the fourth image coding apparatus according to the present invention,
A first bit stream is generated by subjecting at least a part of the input video signal to a predetermined predictive coding and / or a predetermined transform coding process, a quantization process at a fixed quantization step size, and a variable length coding process. The coding rate for each predetermined time is determined based on the data amount of the first bit stream and the total amount of usable data. Then, a predetermined predictive encoding and / or a predetermined transform encoding process is performed on the input video signal,
Quantization processing at a quantization step size based on the encoding rate for each predetermined time and variable-length encoding
Generate a bitstream of.

In the fifth image encoding apparatus according to the present invention,
In the fourth image encoding device, an encoding rate is determined for each frame based on the amount of data for each frame in the first bit stream and the total amount of usable data. The input video signal is subjected to a predetermined predictive coding and / or a predetermined transform coding process, a quantization process at a quantization step size based on a coding rate for each frame, and a variable length coding process. 2 bit streams are generated.

In the sixth image coding apparatus according to the present invention,
In the fourth image encoding device, GO is determined based on at least a part of the data amount of each GOP including a plurality of frames in the first bit stream and the total available data amount.
An encoding rate is obtained for each P. Then, a predetermined predictive coding and / or a predetermined transform coding process is performed on the input video signal,
A second bit stream is generated by performing a quantization process at a quantization step size based on the coding rate for each OP and a variable length coding process.

In the seventh image encoding apparatus according to the present invention,
In the sixth image encoding device, the encoding rate for each GOP is obtained based on the data amount of the intra-encoded image and the forward prediction encoded image in the GOP. The input video signal is subjected to predetermined predictive coding and / or predetermined transform coding processing, quantization processing at a quantization step size based on the coding rate for each GOP, and variable length coding processing. Generate a bitstream of.

In the eighth image encoding apparatus according to the present invention,
In the fourth image encoding device, the total amount of usable data is proportionally distributed according to the amount of data of the first bit stream for each predetermined time, and an encoding rate for each predetermined time is obtained. Then, the input video signal is subjected to predetermined predictive coding and / or predetermined transform coding processing, quantization processing at a quantization step size based on a coding rate at predetermined time intervals, and variable length coding processing, and 2 bit streams are generated.

In a ninth image encoding apparatus according to the present invention,
The encoding difficulty is determined for each predetermined image unit of the input video signal, and the encoding rate is set for each predetermined image unit based on the encoding difficulty and the total amount of usable data. Then, the input video signal is encoded such that the encoding rate of each image unit matches the set encoding rate of each image unit.

In a tenth image encoding apparatus according to the present invention, in the ninth image encoding apparatus, the difficulty of encoding is determined for each frame of the input video signal, and the encoding rate is determined for each frame. Then, the input video signal is encoded such that the encoding rate of each frame matches the set encoding rate of each frame.

In an eleventh image encoding apparatus according to the present invention, in the ninth image encoding apparatus, the G
The encoding difficulty is determined for each OP, and the encoding rate is determined for each GOP. Then, the input video signal is encoded such that the encoding rate of each GOP matches the set encoding rate of each GOP.

In a twelfth image encoding apparatus according to the present invention, in the ninth image encoding apparatus, at least a portion of the input video signal is subjected to predetermined predictive coding and / or predetermined transform coding. The difficulty of encoding is obtained by quantizing the coefficient data to be obtained with a fixed quantization step size. Then, the input video signal is encoded such that the encoding rate of each image unit matches the set encoding rate of each image unit.

The first image recording medium according to the present invention has a first image recording medium obtained by encoding at least a part of an input video signal.
A coding rate for each predetermined time is obtained based on the data amount of the coded data for each predetermined time and the total amount of usable data, and the input video signal is obtained for every predetermined time based on this coding rate. A second bit stream is recorded.

In the second image recording medium according to the present invention, at least a part of the input video signal has a predetermined predictive coding and / or
Alternatively, a first bit stream is generated by performing a predetermined transform coding process, a quantization process and a variable length coding process at a fixed quantization step size, and the data amount of the first bit stream and usable data. An encoding rate for each predetermined time is obtained based on the total amount. Then, the input video signal is obtained by performing predetermined predictive coding and / or predetermined transform coding processing, quantization processing at a quantization step size based on a coding rate at predetermined time intervals, and variable length coding processing. A second bit stream to be recorded is recorded.

In the third image recording medium according to the present invention, the difficulty of encoding is determined for each predetermined image unit of the input video signal, and the predetermined degree is determined based on the difficulty of encoding and the total amount of usable data. The coding rate is set for each image unit. Then, coded data obtained by coding the input video signal so that the coding rate of each image unit matches the set coding rate of each image unit is recorded.

[0094]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image encoding method, an image encoding device, and an image recording medium according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, for example, an image encoding apparatus to which the present invention is applied includes a first encoding circuit 10 for encoding an input video signal to generate first encoded data;
A coding control circuit 30 for obtaining a coding rate for each predetermined time based on a data amount of the first coded data from the coding circuit 10 for each predetermined time and a total amount of usable data;
A second encoding circuit that encodes the input video signal at predetermined time intervals based on the encoding rate from the encoding control circuit to generate second encoded data.

Further, as shown in FIG. 1 described above, the first encoding circuit 10 includes a frame memory group 12 for storing input image data, which is an input video signal, and an image data group stored in the frame memory group 12. Vector detection circuit 11 for detecting a motion vector of input image data based on
And a frame memory 22 for storing predicted image data;
A motion compensation circuit 23 that performs motion compensation on predicted image data read from the frame memory 22 based on a motion vector from the motion vector detection circuit 11, and a motion compensated predicted image data from the motion compensation circuit 23. hand,
A predictive coding circuit 14 for predictive coding input image data;
A difference or the like which is a prediction error from the prediction coding circuit 14 is coded, for example, a discrete cosine transform (hereinafter, DCT: Discrete Cosin).
e Transform) to generate coefficient data
A quantization circuit 16 that quantizes the coefficient data from the DCT circuit 15 with a fixed quantization step size to generate quantized data, and a variable-length coding of the quantized data from the quantization circuit 16. , A variable length coding (VLC: Variable Length Code) circuit 17 for outputting variable length code data, and an inverse quantization circuit 18 for inversely quantizing the quantized data from the quantization circuit 16 to reproduce coefficient data.
And the coefficient data from the inverse quantization circuit 18, for example, inverse discrete cosine transform (hereinafter referred to as IDCT: Inverse Discrete C)
ID which reproduces the difference by “sine transform”
The difference between the CT circuit 20 and the IDCT circuit 20 and the motion-compensated predicted image data from the motion compensation circuit 23 are added to generate predicted image data for the next input image data, and the predicted image data is stored in the frame memory 22. And an adder circuit 21 for supplying.

Further, as shown in FIG. 1, the second encoding circuit 40 includes a delay unit 43 for delaying the input image data.
And a frame memory 52 for storing predicted image data;
A motion compensation circuit 53 for performing motion compensation on the predicted image data read from the frame memory 52 based on the motion vector from the motion vector detection circuit 11;
3, a prediction encoding circuit 44 that predictively encodes the input image data delayed by the delay unit 43 based on the motion-compensated prediction image data, and a difference from the prediction encoding circuit 44. A DCT circuit 45 that performs DCT conversion to generate coefficient data, a quantization scale setting circuit 33 that sets a quantization step size based on an encoding rate from the encoding control circuit 30, and a coefficient data from the DCT circuit 45 A quantization circuit 46 that quantizes with the quantization step size from the quantization scale setting circuit 33 to generate quantized data, and a variable length code of the quantized data from the quantization circuit 46 to convert the variable length code data A VLC circuit 47 for outputting, a transmission buffer memory 49 for temporarily storing the variable length code data from the VLC circuit 47, and outputting the same at a constant bit rate; An inverse quantization circuit 48 to reproduce coefficient data to inverse quantization to the quantized data from the circuit 46,
The coefficient data from the inverse quantization circuit 48 is decoded, for example, I
An IDCT circuit 50 that performs DCT conversion and reproduces a difference;
An addition circuit 51 that adds the difference from the DCT circuit 50 and the motion-compensated predicted image data from the motion compensation circuit 53 to generate predicted image data for the next input image data, and supplies the predicted image data to the frame memory 52 And

In this image encoding apparatus, the first encoding circuit 10 encodes the input image data,
For example, the encoding control circuit 30 performs a predictive encoding process, a DCT transform process, a quantization process with a fixed quantization step size, and a variable length encoding process. And the total available data determined by the data capacity of the image recording medium 55 such as an optical disk, a magnetic disk, a magnetic tape, or the like, or the bit rate (transfer rate) of the transmission path. After obtaining the coding bit rate, the second coding circuit 40 performs predictive coding processing, DCT transform processing, quantization processing again on the input image data.
When performing variable length coding processing to generate variable length code data as a second bit stream, quantization is performed with a quantization step size based on the coding bit rate.

That is, in this image coding apparatus, as shown in FIG. 2, for example, in step ST1, the quantization circuit 16 of the first coding circuit 10 sets the quantization step size to, for example, 1 and sends it to the DCT circuit 15 from the DCT circuit 15. The supplied coefficient data is quantized to generate quantized data, and the counter 31 of the encoding control circuit 30 performs variable-length coding on the quantized data to obtain variable-length code data (first bit stream). Is counted for a predetermined period of time, for example, for each frame, and a generated code amount indicating the difficulty of encoding is obtained for each frame.

In step ST2, the bit rate calculation circuit 32 determines the degree of difficulty (the amount of generated code) for each frame,
Based on the total amount of usable data, an assigned code amount assigned to each frame is obtained.

In step ST3, the quantization circuit 46 of the second encoding circuit 40 quantizes the coefficient data supplied from the DCT circuit 45 with a quantization step size based on the allocated code amount, and Is generated.

Specifically, the input image data is temporarily stored in the frame memory group 12. Then, the data is read from the frame memory group 12 according to the block format as described in the related art.

The motion vector detecting circuit 11 reads necessary image data from the frame memory group 12 in the above-described macroblock unit, and detects a motion vector. That is, the motion vector detection circuit 11
Using the forward original image and / or the backward original image stored in 2, the motion vector of the current reference image is detected in macroblock units. Here, in detecting a motion vector, for example, a motion vector in which the sum of absolute values of differences between frames in a macroblock unit is minimized is set as the motion vector. Then, the detected motion vector is added to the motion compensation circuits 23 and 53.
The sum of the absolute values of the differences between the frames in macroblock units is supplied to the intra-frame / forward / backward / bidirectional prediction determination circuit 13.

The intra / forward / backward / bidirectional prediction determination circuit 13 determines the prediction mode of the reference block based on this value, and, based on the determined prediction mode, the intra / forward / backward prediction for each block. / Controls the prediction encoding circuit 14 to switch between bidirectional prediction.

As shown in FIG. 1, the predictive encoding circuit 14 includes adders 14a, 14b, 14c and a changeover switch 14d. In the intra-frame encoding mode, the input image data itself is forward / backward. In the case of the bidirectional prediction mode, a difference (hereinafter referred to as difference data) of each pixel of input image data with respect to each predicted image is selected, and the selected data is supplied to the DCT circuit 15.

The DCT circuit 15 uses the two-dimensional correlation of the video signal to perform DCT conversion on the input image data or difference data supplied from the changeover switch 14d in block units, and outputs the obtained coefficient data to the quantization circuit 16. Supply.

The quantization circuit 16 sets a fixed quantization step size, for example, a quantization step size to 1
The coefficient data supplied from the T circuit 15 is quantized, and the obtained quantized data is converted to the VLC circuit 17 and the inverse quantization circuit 1.
8

The VLC circuit 17 performs variable length coding on the quantized data together with the quantization step size, prediction mode, motion vector, etc., and supplies the obtained variable length code data to the coding control circuit 30 as a first bit stream. I do.

As shown in FIG. 1 described above, the encoding control circuit 30 includes a counter 31 for counting the amount of variable-length code data from the VLC circuit 17 for each predetermined time,
And a bit rate calculation circuit 32 for calculating an allocated code amount per predetermined time based on the data amount from 1 and the total amount of usable data. Then, the counter 31 counts the data amount of the first bit stream every predetermined time, for example, every frame, finds the difficulty for each frame, and supplies this difficulty to the bit rate calculation circuit 32.

The bit rate calculation circuit 32 calculates the allocated code amount allocated to each frame, that is, the average coding rate for each frame time, based on the difficulty level for each frame and the total amount of usable data. The code amount is supplied to the quantization scale setting circuit 33 of the second coding circuit 40.

More specifically, the bit rate operation circuit 32
Indicates that the total number of frames is N and the total amount of usable data is B
And then, i (i = 0,1,2 ··· N -1) th frame difficulty of the (generated code amount) and _{d i,} the assigned code amount for the i-th frame as _{b i,} the assigned code Quantity b
If is proportional to the degree of difficulty d _i to indicate _i by the following formula 1,
Data amount B is as shown in the following formula 2, obtained by adding the allocated code quantity b _i of all frames. Note that a is a constant.

[0112]

(Equation 1)

[0113] Accordingly, constant a can be obtained by the following formula 3, and substituting this constant a into the formula 1, the assigned code amount b _i for the i-th frame, it can be determined by the following equation 4.

[0114]

(Equation 2)

Thus, the bit rate operation circuit 32
For example, the frame of the picture is complex image by increasing the assigned code amount b _i, for the simple picture frame to reverse to reduce the allocated code quantity b _i.

On the other hand, the inverse quantization circuit 18
The quantization data supplied from 6 is inversely quantized with the quantization step size set to 1, and coefficient data (to which quantization distortion is added) corresponding to the output of the DCT circuit 15 is reproduced. It is supplied to the IDCT circuit 20.

The IDCT circuit 20 converts the coefficient data into an IDC
T-transform and reproduce input image data corresponding to the output of the predictive coding circuit 14 in the intra-frame coding mode, and reproduce difference data in the forward / backward / bidirectional prediction mode.
It is supplied to the addition circuit 21.

In the forward / backward / bidirectional prediction mode, the addition circuit 21 is supplied with the predicted image data which has been motion-compensated from the motion compensation circuit 23, and the difference between the predicted image data and the IDCT supplied from the IDCT circuit 20. By adding the data, the image data corresponding to the input image data is reproduced.

The image data thus reproduced is stored in the frame memory 22 as predicted image data. That is, the inverse quantization circuit 18 to the addition circuit 21
Constitutes a local decoding circuit, based on the prediction mode,
The quantized data output from the quantization circuit 16 is locally decoded, and the obtained decoded image is written to the frame memory 22 as a forward predicted image or a backward predicted image. The frame memory 22 is composed of a plurality of frame memories, a bank switching of the frame memories is performed, and, for example, a single frame is output as forward predicted image data or backward predicted image data according to an image to be encoded. Is output. In the case of forward / backward / bidirectional prediction, forward predicted image data and backward predicted image data are averaged and output, for example. These prediction image data are exactly the same image data as the image data reproduced by the image decoding device described later, and the next processed image is subjected to forward / backward / bidirectional prediction coding based on this prediction image. Will be

Next, the operation of the second encoding circuit 40 will be described. The circuits other than the quantization scale setting circuit 33, the delay unit 43, the quantization circuit 46, and the transmission buffer memory 49 constituting the second encoding circuit 40 are the circuits constituting the first encoding circuit 10 described above. Since the same operation as described above is performed, the description is omitted.

The delay unit 43 delays the input image data, for example, until a coding control signal is output from the coding control circuit 30. Then, the predictive encoding circuit 44, DC
In the T circuit 45, the delayed input image data is subjected to a predictive encoding process and a DCT transform process according to the prediction mode supplied from the intra-frame / forward / backward / bidirectional prediction determination circuit 13 to generate coefficient data. You.

The quantization scale setting circuit 33 calculates the allocated code amount for each macroblock (for example, by dividing the allocated code amount for each frame by the number of macroblocks in one frame) from the supplied allocated code amount for each frame. Then, a comparison is made between the generated code amount generated in the macroblock detected from the buffer feedback from the transmission buffer 49 and the allocated code amount for each macroblock.
When the quantization scale setting circuit 33 approaches the coding bit rate of each frame and the average coding bit rate for each set frame time, the generated code amount in the macro block is larger than the allocated code amount for each macro block. If the quantization step size of the next macroblock is set large to suppress the generated code amount of the next macroblock, and if the generated code amount in the macroblock is smaller than the allocated code amount for each macroblock, the generated code amount , The quantization step size of the next macroblock is reduced. However, when the buffer feedback from the transmission buffer 49 indicates that the overflow of the transmission buffer 49 is near, the quantization scale setting circuit 33 performs quantization regardless of the result of comparison between the allocated code amount and the generated code amount. When the overflow is suppressed by increasing the step size, and the buffer feedback from the transmission buffer indicates that the underflow of the transmission buffer 49 is near, regardless of the result of comparing the allocated code amount and the generated code amount described above. The underflow is suppressed by reducing the quantization step size. In the above description,
Although the generated code amount and the allocated code amount are compared for each macroblock and the quantization step size is switched for each macroblock, the switching may be performed for each slice. Further, in the above description, the amount of generated codes is detected from the amount of accumulation in the transmission buffer 49, but can be directly obtained from the output of the variable length coding circuit 47. The quantization scale setting circuit 33 supplies the quantization step size thus set to the quantization circuit 46.

The quantization circuit 46 quantizes the coefficient data supplied from the DCT circuit 45 according to the quantization step size supplied from the above-described quantization scale setting circuit 33 to generate quantized data.

The VLC circuit 47 has a quantization circuit 4
6, the quantization step size from the quantization scale setting circuit 33, the prediction mode from the intra / forward / backward / bidirectional prediction determination circuit 13,
Variable-length coding is performed together with the motion vector and the like from the motion vector detection circuit 11, and the obtained variable-length code data is supplied to the transmission buffer memory 49 as a second bit stream.

That is, in this image encoding apparatus, as shown in FIG. 3, for example, when image data is input via the delay unit 43 in step ST1, the process proceeds to step ST1.
In step 2, the quantization scale setting circuit 33 reads, from the encoding control circuit 30, the code amount allocated to the frame currently being encoded, and proceeds to step ST3.

In step ST3, the predictive coding circuit 44 to the VLC circuit 47 perform the predictive coding process and the DCT transform process on the image data, and quantize the coefficient data by the quantization step size based on the allocated code amount. Thereafter, variable-length coding is performed, and the process proceeds to step ST4.

In step ST4, for example, it is determined whether or not the encoding process has been completed for all frames (sequences) to which the same screen size and the same transfer rate are applied. Returns to step ST1. In this way, variable rate coding in which the coding rate is changed in frame units is realized, and even if images (frames) having complicated patterns continue, the quantization step size for these images is increased as in the conventional device. Without this, uniform high image quality can be obtained throughout.

The transmission buffer memory 49 temporarily stores the variable-length code data, reads out the variable-length code data at a constant bit rate, and smoothes the variable-length code data to output it as a bit stream. The bit stream output from the transmission buffer memory 49 is multiplexed with, for example, an encoded audio signal, a synchronization signal, and the like, further added with an error correction code, and subjected to predetermined modulation suitable for transmission or recording. After being added, it is transmitted to an image decoding device via a transmission path, for example, or
As shown in (1), it is recorded on an image recording medium 55 composed of an optical disk, a magnetic disk, a magnetic tape or the like. That is,
In the second encoding circuit 40, for example in advance for the complex image by increasing the assigned code amount b _i, for the simple image subjected to variable rate encoding by reducing the allocated code quantity b _i Therefore, it is not necessary to apply a fixed rate of a high rate throughout the entire image in order to avoid extreme image quality degradation for an image having a complicated pattern as in the conventional apparatus, and to increase the recording time of the image recording medium 55. can do.

On the other hand, the inverse quantization circuit 48 includes the quantization circuit 4
6 is supplied to the above-described quantization circuit 4
6 is inversely quantized by the quantization step size used in
The coefficient data (to which the quantization distortion is added) corresponding to the output of the DCT circuit 45 is reproduced, and
It is supplied to the CT circuit 50. That is, the inverse quantization circuit 48 to the addition circuit 51 constituting the local decoding circuit locally decode the quantized data output from the quantization circuit 46, and use the obtained decoded image as a forward prediction image or a backward prediction image as a frame. Write to the memory 52. Frame memory 5
The image data stored in 2 is used as a predicted image for the next processed image.

In the above embodiment, the allocated code amount per predetermined time, that is, the average coding rate per predetermined time is obtained for each frame by using the frame as the predetermined time. However, the present invention is not limited to this. It is not something to be done. For example, a so-called MPEG (Moving Picture Expert)
A GOP (Group of Picture) in a Group) may be set as a predetermined time. The above-mentioned MPEG is a so-called ISO.
(International Organization for Standardization) and IEC (International Electrotechnical Commission) J
SC (S) at TC (Joint Technical Committee) 1
ub Committee) 29 is a common name for a moving picture coding method under consideration in a WG (Working Group) 11.

That is, a GOP in MPEG is composed of at least one so-called I picture and a plurality of P pictures or B pictures (non-I pictures). Specifically, for example, as shown in FIG. 4, one I picture, four P pictures in a three-picture cycle, and ten B pictures
If the encoding control circuit 3
0 calculates the assigned code amount for each GOP. Here, an I picture is an image that is coded in a field or an intra-frame, and a P picture is an image that can be predicted only from the forward direction and is coded between a field or an inter-frame. Is an image that can be predicted from the forward direction, from the backward direction, and from both directions, and is encoded between fields or between frames.

Then, in the first encoding circuit 10,
For example, as shown in FIG. 5, two consecutive pictures in a GOP are tentatively defined as an I picture and a P picture with the number of pictures constituting the GOP as a cycle, and the quantization step size is set to 1, for example. Predictive coding processing for image data of I picture and P picture, DCT
A conversion process and a variable-length coding process are performed to generate variable-length code data, and the variable-length code data is
Supply 0. Here, two pictures are I pictures,
The P picture is used to check the complexity of the picture and the correlation between the frames. The complexity of the picture can be known from the generated code amount of the I picture. We can know the correlation. Generally, since a plurality of continuous frames have similar images, the tendency of the picture of the GOP can be seen even from the two extracted pictures.

[0133] The coding control circuit 30 is configured to count the data amount BITP _j data amount Biti _j and P picture of the I picture in each GOP, for example, as shown in the following formula 5, these data amount Biti _j, BITP _{Based on j} and the number N of P pictures constituting the GOP, a difficulty level (generated code amount) GOPd _j (j = 0, 1, 2,...) is obtained for each GOP.

[0134] Then _{GOPd j = bitI j + N ×} bitP j ··· Equation 5, the encoding control circuit 30, and the GOP for each of difficulty (amount of generated code) GOPd _j, based on the available data amount, The allocated code amount allocated to each GOP is obtained, and the allocated code amount is supplied to the second encoding circuit 40.

Specifically, the total number of GOPs is M, the total amount of usable data is B, the code amount allocated to the j-th GOP is GOPb _j , and the allocated code amount GOPb _j is expressed by the following equation (6). The total data amount B is obtained by adding the allocated code amounts GOPb _j of all the GOPs as shown in the following Expression 7. Note that a
Is a constant.

[0136]

(Equation 3)

Accordingly, the constant a can be obtained by the following equation 8, and by substituting this constant a into the equation 6, the allocated code amount GOPb _j for the j-th GOP can be obtained by the following equation 9.

[0138]

(Equation 4)

Thus, the coding control circuit 30 increases the allocated code amount GOPb _j for a GOP containing a picture having a complicated pattern or having a low correlation between frames, for example. For a GOP that is included or has a high correlation between frames, the allocated code amount GOPb _j
Less.

Next, as shown in FIG. 6, for example, as shown in FIG.
When the image data is input through the step ST2, in step ST2, it is determined whether the currently input image data is the first picture of the GOP. If the image data is applicable, the process proceeds to step ST3, and if not, the process proceeds to step ST4.

At step ST3, the second coding circuit 40 reads the code amount allocated to the GOP currently to be coded from the coding control circuit 30, and proceeds to step ST4.

In step ST4, the second encoding circuit 40 performs the predictive encoding process and the DCT transform process on the image data, and quantizes the coefficient data by the quantization step size based on the allocated code amount. Variable length coding is performed, and the process proceeds to step ST5.

Here, the quantization scale setting circuit 33
From the supplied allocated code amount for each GOP, the allocated code amount for each frame is determined by the picture type (I
Picture, P picture, B picture), that is, the picture type shown in FIG. Specifically, the allocated code amount for the I picture is increased, the allocated code amount for the B picture is reduced, and the allocated code amount for the P picture is set in the middle. Subsequent processing of the quantization scale setting circuit 33 is the same as that of the embodiment in which the allocated code amount is obtained for each frame described above.

Next, in step ST5, it is determined whether or not the encoding process has been completed for all frames (sequences) to which the same screen size and the same transfer rate are applied. If it is, the process returns to step ST1. In this way, variable rate coding in which the coding rate is changed in GOP units is realized, and even if images (frames) having complicated patterns continue, the quantization step size for these images is increased as in the conventional apparatus. Without this, uniform high image quality can be obtained throughout. Further, in this embodiment, since the allocated code amount for each GOP is obtained based on two pictures, high-speed processing is possible as compared with the above-described embodiment. It is needless to say that the allocated code amount of each GOP may be obtained based on the data amount of all pictures in the GOP.

Note that the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the transform coding is performed by DCT, but the so-called strat transform, Haar transform, wavelet transform, etc. Is also good.

[0146]

As is apparent from the above description, according to the present invention, an input video signal is encoded, for example, predictive encoding, DCT
Transformation, quantization at a fixed quantization step size, and variable-length encoding to generate first encoded data, and for each predetermined time of the first encoded data, for example, for each frame or GOP, By calculating the assigned code amount for each frame or GOP based on the total amount of usable data, and encoding the input video signal at predetermined time intervals based on the assigned code amount to generate second encoded data, Variable-rate coding in which the coding rate is changed at predetermined time intervals is realized, and even if images (frames) having complicated patterns continue, the quantization step size is increased for these images as in the conventional device. Therefore, uniform high image quality can be obtained throughout.

Further, since the second encoded data obtained as described above has a variable rate, by recording this on an image recording medium, a limited recording capacity can be used effectively, and The recording time of the recording medium can be lengthened. Then, uniform high-quality image data can be reproduced from the image recording medium throughout.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of a main part of an image encoding device to which the present invention has been applied.

FIG. 2 is a flowchart illustrating an operation of a first encoding circuit included in the image encoding device.

FIG. 3 is a flowchart illustrating an operation of a second encoding circuit included in the image encoding device.

FIG. 4 is a diagram showing each picture for explaining the structure of a GOP in MPEG.

FIG. 5 is a diagram illustrating each picture for describing an encoding control signal for each GOP.

FIG. 6 is a flowchart for explaining an operation of a second encoding circuit forming the image encoding device.

FIG. 7 is a diagram showing an image for explaining the principle of predictive coding.

FIG. 8 is a diagram showing an image for explaining the principle of motion compensated prediction coding.

FIG. 9 is a block diagram illustrating a configuration of an image encoding device and an image decoding device.

FIG. 10 is a diagram illustrating a configuration of a macroblock and a slice.

FIG. 11 is a block diagram showing a circuit configuration of a conventional encoder.

FIG. 12 is a block diagram showing a circuit configuration of a conventional decoder.

[Explanation of symbols]

10 first encoding circuit, 11 motion vector detection circuit, 12 frame memory group, 13 intra / forward / backward / bidirectional prediction determination circuit, 14 prediction encoding circuit,
15 DCT circuit 15, 16 Quantization circuit, 17 VL
C circuit, 18 inverse quantization circuit, 20 IDCT circuit, 2
1 addition circuit, 22 frame memory, 23 motion compensation circuit, 30 encoding control circuit, 31 counter, 32 bit rate operation circuit, 33 quantization scale setting circuit,
40 second encoding circuit, 43 delay unit, 44 predictive encoding circuit, 45 DCT circuit, 46 quantization circuit, 47
VLC circuit, 48 inverse quantization circuit, 49 transmission buffer memory, 50 IDCT circuit, 51 addition circuit, 52
Frame memory, 53 Motion compensation circuit, 55 Image recording medium

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[Procedure amendment]

[Submission date] December 27, 2000 (200.12.
27)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Image encoding method and image encoding device

[Claims]

(Equation 1) Here, M is the number of the GOP, and j is 1 to M−
GOPd _j is the assigned code amount for the j-th GOP, B is the total amount of usable data for the plurality of GOPs determined by the bit rate of the transmission path, and GOPd _j is the j-th GOP. Is the difficulty of encoding the GOP.

(Equation 2) Here, M is the number of the GOP, and j is 1 to M−
GOPd _j is the assigned code amount for the j-th GOP, B is the total amount of usable data for the plurality of GOPs determined by the bit rate of the transmission path, and GOPd _j is the j-th GOP. Is the difficulty of encoding the GOP.

(Equation 3) Here, N is the number of the plurality of images, and i is 1 to
An N-1 integers, b _i is the assigned code amount for the i-th image, B is the total amount of data corresponding to the plurality of images, d _i is the encoding of the i-th image Difficulty.

(Equation 4) Here, N is the number of the plurality of images, and i is 1 to
An N-1 integers, b _i is the assigned code amount for the i-th image, B is the total amount of data corresponding to the plurality of images, d _i is the encoding of the i-th image Difficulty.

(Equation 5) Here, N is the number of the plurality of images, and i is 1 to
An N-1 integers, b _i is the assigned code amount for the i-th image, B is the total amount of data corresponding to the plurality of images, d _i is the encoding of the i-th image Difficulty.

(Equation 6) Here, N is the number of the plurality of images, and i is 1 to
An N-1 integers, b _i is the assigned code amount for the i-th image, B is the total amount of data corresponding to the plurality of images, d _i is the encoding of the i-th image Difficulty.

(Equation 7) Here, N is the number of the plurality of images, and i is 1 to
An N-1 integers, b _i is the assigned code amount for the i-th image, B is the total amount of data corresponding to the plurality of images, d _i is the encoding of the i-th image Difficulty.

(Equation 8) Here, N is the number of the plurality of images, and i is 1 to
An N-1 integers, b _i is the assigned code amount for the i-th image, B is the total amount of data corresponding to the plurality of images, d _i is the encoding of the i-th image Difficulty.

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method and an image encoding apparatus, and more particularly to a system for encoding and recording moving image video signals on an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape. And a system for transmitting a video signal of a moving image via a transmission path.

[0002]

2. Description of the Related Art Conventionally, a system for transmitting a video signal of a moving image to a remote place, such as a video conference system and a video telephone system, and a video signal of a moving image are recorded on an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape. In a system or the like for reproducing a video signal of a recorded moving image, in order to efficiently use a transmission path (or an image recording medium), a video signal is so-called utilizing a line correlation or a frame correlation of the video signal. High-efficiency coding is performed to reduce the redundancy in the space axis direction and the time axis direction and transmit only significant information, thereby improving transmission efficiency.

For example, in an encoding process in the spatial axis direction (hereinafter referred to as an intra-frame encoding process), as shown in FIG.
For example, a line correlation of a video signal is used.
Each image P constituting a moving image at 1, t2, t3,.
When trying to transmit C1, PC2, PC3 ...
The image data to be transmitted is, for example, 1 in the same scanning line.
Data compression is performed by two-dimensional encoding or by dividing an image into a plurality of blocks and two-dimensionally encoding the image data of each block, thereby improving transmission efficiency.

In the encoding process in the time axis direction (hereinafter referred to as inter-frame encoding process), for example, so-called predictive encoding is performed using inter-frame correlation of a video signal, that is, as shown in FIG. Matching image PCl and PC
2, image data PC1 which is a difference (a so-called prediction error) of the image data of each corresponding pixel between PC2 and PC3.
2, PC23..., And these image data PC1
2, data is compressed by transmitting the PC 23, and the transmission efficiency is improved.

[0005] Thus, the images PC1, PC2, PC3
The video signal can be transmitted with a much smaller data amount than when all the image data is transmitted.

In the above-described predictive coding in the inter-frame coding process, for example, motion compensation prediction is used for each macroblock in order to further increase the efficiency. That is, for example, when a person in the center of the screen moves, the movement of a moving object on the screen is detected, and the position of the image data used for prediction in the image preceding by the movement is corrected to perform the prediction. By performing the encoding, the encoding efficiency can be improved. However, even now, much data must be sent to the part where the object moves and appears from behind. Therefore, the coding efficiency can be further improved by performing the motion compensation prediction not only in the above-mentioned forward direction but also in the backward direction or in a combination of both.

Specifically, as shown in FIG. 8A, frame data F0, F1,... Of the 0th, 1st, 2nd, 3rd,...
In the macroblocks F2, F3,..., When there is a change in the image as represented by the motion vectors X0, X1, X2, X3,. Every second (for example, one frame), that is, the second, fourth,..., Frames are designated as interpolation frames.
As shown in B, transmission interpolation frame data F2X, F4X... Are generated by predetermined interpolation frame processing. In addition, the frame data F
, F3... Are subjected to a predetermined encoding process to generate transmission non-interpolated frame data F1X, F3X.

For example, motion-compensated frame data F
3 and the frame data F2, the difference SP2 (prediction error), the motion-compensated frame data F1 and the frame data F2
, The motion-compensated frame data F1, F2
Then, a difference SP4 between the frame data and the frame data F2 obtained by performing the interpolation process on No. 3 is obtained for each macroblock, and the difference between the macroblock SP1 of the frame data F2 and these differences is compared. And these data SP
1 to SP4, the data with the smallest data generation amount is referred to as transmission interpolation data F2X in macroblock units, and so on.
... is generated. Also, for example, the non-interpolated frame data F1, F3,... Are subjected to, for example, DCT conversion processing, variable-length coding processing, etc. to generate transmission non-interpolated frame data F1X, F3X.

The transmission non-interpolated frame data F1X, F3X...
.. Together with the data of the motion vectors X0, X1, X3,... As transmission data DATA to the device on the receiving side.

On the other hand, the apparatus on the receiving side transmits transmitted data DATA (transmitted non-interpolated frame data F1X, F3X
,..., Transmission interpolation data F2X, F4X,..., Motion vectors X0, X1, X3,. , F2, F3,... As a result, the coding efficiency can be further improved by performing the motion compensation prediction not only in the forward direction but also in the backward direction or in a combination of the two directions.

Here, an image encoding apparatus and an image decoding apparatus having the above-described functions will be described.

As shown in FIG. 9, the image encoding apparatus 60 includes a pre-processing circuit 61 for separating an input video signal VD into a luminance signal and a color difference signal, a luminance signal from the pre-processing circuit 61,
Analog / digital (hereinafter referred to as A / D) conversion circuits 62a and 62 for converting color difference signals into digital signals, respectively.
2b, a frame memory group 63 for storing luminance data and color difference data (hereinafter referred to as image data) from the A / D conversion circuits 62a and 62b, and a frame memory group 63
A format conversion circuit 64 for reading out image data from the format conversion circuit 64 in accordance with a block format, and an encoder 65 for encoding the image data of the block from the format conversion circuit 64 with high efficiency.

The pre-processing circuit 61 separates the input video signal VD into a luminance signal and a chrominance signal.
2a and 62b convert the luminance signal and the chrominance signal into 8-bit luminance data and chrominance data, respectively, and the frame memory group 63 stores these luminance data and chrominance data.

The format conversion circuit 64 converts the image data (luminance data,
Color difference data) according to a block format, and the encoder 65 encodes the read image data by predetermined high-efficiency encoding, and outputs a bit stream.

The bit stream is supplied to an image decoding device 80 via a transmission path or a transmission medium 70 including an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape.

As shown in FIG. 9 described above, the image decoding apparatus 80 includes a decoder 81 corresponding to the encoder 65.
A format conversion circuit 82 for converting the image data reproduced by the decoder 81 into a frame format,
A frame memory group 83 for storing image data from the format conversion circuit 82; D / A conversion circuits 84a and 84b for converting luminance data and color difference data read from the frame memory group 83 into analog signals; A post-processing circuit 85 that mixes the luminance signal and the color difference signals from the conversion circuits 84a and 84b to generate an output video signal.

The decoder 81 includes an encoder 65
The bit stream is decoded by decoding corresponding to the high-efficiency encoding to reproduce the image data in the block format, and the format conversion circuit 82 converts the image data into the frame format, and
3 is stored.

The D / A conversion circuits 84a and 84b convert the luminance data and chrominance data read from the frame memory group 83 into a luminance signal and a chrominance signal, respectively. The signals are mixed to generate an output video signal.

Specifically, the preprocessing circuit 61 and the A / D conversion circuits 62a and 62b convert the luminance signal and the color difference signal into digital signals as described above, The number of pixels is の of the luminance signal
After reducing the amount of data so that
The obtained luminance data and color difference data are stored in a frame memory group 6
Supply 3

The luminance data and the color difference data are read from the frame memory group 63 in accordance with the block format as described above. That is, for example, image data for one frame is divided into N slices as shown in FIG. 10A, and each slice includes M macroblocks as shown in FIG. As shown in FIG. 10C, the block is a block unit composed of 8 × 8 pixels, and luminance data Y1, Y2, Y3, and Y4 of four luminance blocks adjacent vertically, horizontally, and
The color difference data includes color difference data Cb and Cr of a color difference block composed of 8 × 8 pixels in a range corresponding to these four luminance blocks. Then, from the frame memory group 63, image data continues in units of macroblocks in the slice, and Y1, Y2, Y3, Y4, Cb, C
The luminance data and the color difference data are read so as to be continuous in the order of r. The image data read according to the block format in this manner is supplied to the encoder 65.

The encoder 65, as shown in FIG.
A motion vector detection circuit 101 is provided. The motion vector detection circuit 101 detects a motion vector of image data supplied in a block format on a macroblock basis. That is, the motion vector detection circuit 101 detects the motion vector of the current reference image in macroblock units using the front original image and / or the rear original image stored in the frame memory group 63. Here, in the detection of the motion vector, the motion vector in which the sum of the absolute values of the inter-frame differences in the macroblock unit is minimized is set as the motion vector. Then, the detected motion vector is supplied to the motion compensation circuit 113 and the like, and the sum of absolute values of the inter-frame differences in macroblock units is supplied to the intra-frame / forward / backward / bidirectional prediction determination circuit 103.

The intra / forward / backward / bidirectional prediction determination circuit 103 determines the prediction mode of the reference block based on this value, and, based on the determined prediction mode, the intra / forward prediction frame for each macroblock. The prediction encoding circuit 104 is controlled so as to switch between / backward / bidirectional prediction. Then, the predictive encoding circuit 104
a, 104b, 104c, and a changeover switch 104d. The input image data itself is used in the intra-frame coding mode, and the difference (pixel) of the input image data with respect to each prediction image in the forward / backward / bidirectional prediction mode. The data is supplied to the DCT circuit 105.

The DCT circuit 105 uses the two-dimensional correlation of the video signal to perform DCT on the input image data or difference data in block units and supplies the obtained coefficient data to the quantization circuit 106.

The quantization circuit 106 quantizes the coefficient data using a quantization step size (quantization scale) determined for each macroblock or slice, and encodes the obtained quantized data into a variable length code (VLC: Variable Length).
(Code) circuit 107 and an inverse quantization circuit 108. By the way, the quantization step size used for the quantization is determined by feeding back the remaining buffer amount of the transmission buffer memory 109, which will be described later, so that the transmission buffer memory 109 does not fail. The quantization step size is also determined by the VLC circuit. 107 and inverse quantization circuit 1
08.

The VLC circuit 107 performs variable length coding on the quantized data together with the quantization step size, the prediction mode, and the motion vector, and supplies the data to the transmission buffer memory 109 as transmission data.

The transmission buffer memory 109 stores the transmission data once, reads it out at a constant bit rate, smoothes the transmission data and outputs it as a bit stream, and outputs the bit stream according to the amount of residual data remaining in the memory. Then, the quantization control signal in macroblock units is fed back to the quantization circuit 106 to control the quantization step size. Thereby, the transmission buffer memory 109
Adjusts the amount of data generated as a bit stream and maintains an appropriate amount of data in the memory (a data amount that does not cause overflow or underflow). For example, when the remaining amount of data in the transmission buffer memory 109 increases to the allowable upper limit, the transmission buffer memory 1
In step 09, the data amount of the quantized data is reduced by increasing the quantization step size of the quantization circuit 106 by the quantization control signal. On the other hand, when the remaining amount of data in the transmission buffer memory 109 decreases to the permissible lower limit, the transmission buffer memory 109 reduces the quantization step size of the quantization circuit 106 by the quantization control signal, thereby obtaining the data of the quantized data. Increase volume.

As described above, the bit stream output from the buffer memory 109 is transmitted at a constant bit rate to the transmission path and the transmission medium 70 composed of an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape as described above. The image is supplied to the image decoding apparatus 80 via

On the other hand, the inverse quantization circuit 108 inversely quantizes the quantized data supplied from the quantization circuit 106, and coefficient data (quantization distortion is added thereto) corresponding to the output of the DCT circuit 105 described above. ) Is reproduced, and the coefficient data is subjected to inverse discrete cosine transform (hereinafter, IDCT: Inverse Discrete C).
osine transform).

The IDCT circuit 110 converts the coefficient data into an ID
CT conversion and reproduces image data corresponding to the input image data in the intra-frame encoding mode, and reproduces difference data corresponding to the output of the prediction encoding circuit 104 in the forward / backward / bidirectional prediction mode. 111.
In the forward / backward / bidirectional prediction mode, the addition circuit 111 is supplied with motion-compensated predicted image data from a motion compensation circuit 113 described later, and adds the motion-compensated predicted image data and difference data. By doing so, the image data corresponding to the input image data is reproduced.

The image data thus reproduced is stored in the frame memory 112. That is, the inverse quantization circuit 108 to the addition circuit 111 constitute a local decoding circuit, and the quantization circuit 1
The quantized data output from 06 is locally decoded, and the obtained decoded image is written to the frame memory 112 as a forward predicted image or a backward predicted image. Frame memory 1
Numeral 12 is composed of a plurality of frame memories, the bank switching of the frame memories is performed, and a single frame is output as forward prediction image data or backward prediction image data depending on the image to be encoded. . In the case of bidirectional prediction, forward predicted image data and backward predicted image data are averaged and output, for example. These predicted image data are exactly the same images as the images reproduced by the decoder 81 described later, and the next processed image is subjected to forward / backward / bidirectional prediction encoding based on this predicted image.

That is, the image data read from the frame memory 112 is supplied to the motion compensation circuit 113,
This motion compensation circuit 113 calculates
The motion compensation is performed on the prediction image data, and the motion compensated prediction image data is added to the prediction encoding circuit 104 and the addition circuit 111.
To supply.

Next, the decoder 81 will be described.

A bit stream is input to the decoder 81 via the transmission medium 70. This bit stream is input to a variable length decoding (hereinafter referred to as IVLC) circuit 202 via a reception buffer 201 as shown in FIG. The IVLC circuit 202 reproduces quantized data, a motion vector, a prediction mode, a quantization step size, and the like from the bit stream. These quantization data and quantization step size are supplied to the inverse quantization circuit 203,
The motion vector is supplied to the motion compensation circuit 207, and the prediction mode is supplied to the addition circuit 205.

The operations of the inverse quantization circuit 203 to the addition circuit 205 are the same as those of the local decoding circuit of the encoder 65, and the operations of the frame memory group 206 and the motion compensation circuit 207 are the frame memory 112 and the motion compensation circuit of the encoder 65, respectively. The decoding is performed based on the quantization data, the motion vector, the prediction mode, and the quantization step size. As a result, reproduced image data is output from the addition circuit 205.

As described above, in the conventional apparatus, the encoding bit rate of the bit stream generated by the encoder 65 is fixed in accordance with the transfer rate of the transmission medium 70, and under this restriction, the amount of data generation, that is, The quantization step size of the quantization circuit 106 in the encoder 65 has been controlled. In other words, for example, when images with complicated patterns continue, the quantization step size is increased to suppress the amount of data generation, and conversely, when simple patterns continue, the quantization step size is reduced to reduce the data size. By increasing the generation amount, a fixed rate is maintained without causing an overflow or underflow of the buffer memory 109.

Therefore, in the conventional apparatus, when a complicated image is continuous, the quantization step size is increased,
When the image quality is degraded and simple images continue, the quantization step size is reduced, and it is not possible to obtain uniform image quality throughout.

When a bit stream is recorded on an image recording medium having a limited data capacity, in order to prevent an extreme deterioration in image quality of an image having a complicated pattern, the image quality of the complicated image is not impaired. A higher fixed rate must be applied to the whole, resulting in reduced recording time.

[0038]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method, for example, in which images having complicated patterns It is an object of the present invention to provide an image encoding method and an image encoding device capable of obtaining uniform high image quality throughout without increasing the quantization step size unlike the conventional device.

Another object of the present invention is to make it possible to effectively use a limited recording capacity when recording on an image recording medium, to increase the recording time of image data on the image recording medium, Another object of the present invention is to provide an image encoding method and an image encoding device capable of reproducing uniform high-quality image data throughout from an image recording medium.

[0040]

In order to solve the above-mentioned problems, an image encoding method according to the present invention encodes input image data for each GOP composed of a plurality of images,
Generating first coded data for each GOP, determining the difficulty of encoding for each GOP based on the data amount of the first coded data, The amount of code assigned to each GOP according to the sum of the difficulty of encoding the GOPs is increased for GOPs containing images with complicated patterns, and less for GOPs containing images with simple patterns. Calculating to be assigned, and encoding the input image data for each GOP based on the assigned code amount assigned to each GOP, generating second encoded data, and performing second encoding for each GOP. The data amount of the data is set to the allocated code amount for each GOP.

The image encoding apparatus according to the present invention quantizes input image data for a plurality of GOPs composed of a plurality of images using a fixed quantization step size to generate first encoded data. , A first encoding unit for determining the degree of difficulty of encoding, and a data amount of the first encoded data,
Detecting the degree of difficulty of encoding for each GOP, and determining the amount of code to be assigned to each GOP according to the sum of the degree of difficulty of encoding for each GOP and the degree of difficulty of encoding a plurality of GOPs, including images with complicated patterns Encoding control means for calculating so that a large number is assigned to a GOP and a small number of symbols for a GOP including a simple image, and an assigned code amount assigned to each GOP for each GOP. To generate second encoded data, based on
A second encoding unit configured to make the data amount of the second encoded data for each GOP equal to the allocated code amount for each GOP.

The image encoding method according to the present invention encodes input image data of a plurality of images to generate first encoded data for each image, and reduces the amount of data of the first encoded data. Determining the degree of difficulty of encoding for each image based on the sum of the degree of difficulty of encoding for each image and the degree of difficulty of encoding a plurality of images. And assigning a large number of images to simple images and a small number of images to simple images, and encoding the input image data for each image based on the assigned code amount assigned to each image. To generate second encoded data, and generate a second encoded data for each image.
In such a manner that the data amount of the coded data becomes the allocated code amount for each image.

An image encoding apparatus according to the present invention encodes a plurality of pieces of input image data to generate first encoded data, and reduces the amount of data of the first encoded data. Based on the difficulty of encoding for each image, the amount of code assigned to each image is calculated according to the sum of the difficulty of encoding for each image and the difficulty of encoding a plurality of images. Encoding control means for calculating so that a large number is assigned to a picture and a small number of pictures are assigned to a simple image, and coding input image data for each image based on an assigned code amount assigned to each image. And a second encoding unit that generates the second encoded data and makes the data amount of the second encoded data for each image equal to the allocated code amount for each image.

An image encoding method according to the present invention comprises the steps of: selecting a prediction mode for each of a plurality of images represented by input image data;
Encoding input image data of a plurality of images to generate first encoded data for each pixel; and determining a degree of encoding difficulty for each image based on a data amount of the first encoded data. Calculating an assigned code amount assigned to each image based on the difficulty of encoding for each image; and assigning an input image data for each image using a prediction mode and assigning an assigned code for each image. Encoding based on the amount to generate second encoded data, so that the data amount of the second encoded data for each image becomes the allocated code amount for each image.

[0045] An image coding apparatus according to the present invention comprises: a prediction determining means for selecting a prediction mode for each of a plurality of images represented by input image data; And a first encoding unit that generates first encoded data for each pixel,
Encoding control for determining the degree of encoding for each image based on the data amount of the first encoded data, and calculating the amount of code to be allocated to each image based on the degree of encoding difficulty for each image Means, and encoding the input image data for each image using a prediction mode and based on an assigned code amount assigned to each image to generate second encoded data, and generating a second encoded data for each image. Second encoding means for setting the data amount of the encoded data to be the assigned code amount for each image.

An image encoding method according to the present invention comprises the steps of: detecting a motion vector for each macroblock of a plurality of images represented by input image data; Generating the first encoded data for each image, obtaining the degree of difficulty of encoding for each image based on the data amount of the first encoded data, Calculating the assigned code amount assigned to each image based on the difficulty of encoding; and input image data for each image,
Using the motion vector and encoding based on the assigned code amount assigned to each image, second encoded data is generated, and the data amount of the second encoded data for each image is determined by the assigned code for each image. And the step of providing a quantity.

An image coding apparatus according to the present invention includes a motion vector detecting means for detecting a motion vector for each macroblock of a plurality of images represented by input image data, and a method for converting input image data of a plurality of images. A first encoding unit for encoding using a motion vector to generate first encoded data for each image; and a difficulty level of encoding for each image based on a data amount of the first encoded data. Encoding control means for calculating an assigned code amount assigned to each image based on the degree of difficulty of encoding for each image, and assigning input image data for each image to each image using a motion vector. Is encoded based on the assigned code amount
Is generated so that the data amount of the second encoded data for each image becomes the allocated code amount for each image.
Encoding means.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image encoding method and an image encoding apparatus according to the present invention will be described with reference to the drawings.

An image coding apparatus to which the present invention is applied includes, for example, as shown in FIG. 1, a first coding circuit 10 for coding an input video signal to generate first coded data,
A coding control circuit 30 for obtaining a coding rate for each predetermined time based on a data amount of the first coded data from the coding circuit 10 for each predetermined time and a total amount of usable data;
A second encoding circuit that encodes the input video signal at predetermined time intervals based on the encoding rate from the encoding control circuit to generate second encoded data.

Further, as shown in FIG. 1, the first encoding circuit 10 includes a frame memory group 12 for storing input image data as an input video signal, and an image data group stored in the frame memory group 12. Vector detection circuit 11 for detecting a motion vector of input image data based on
And a frame memory 22 for storing predicted image data;
A motion compensation circuit 23 that performs motion compensation on predicted image data read from the frame memory 22 based on a motion vector from the motion vector detection circuit 11, and a motion compensated predicted image data from the motion compensation circuit 23. hand,
A predictive coding circuit 14 for predictive coding input image data;
A difference or the like which is a prediction error from the prediction coding circuit 14 is coded, for example, a discrete cosine transform (hereinafter, DCT: Discrete Cosin).
e Transform) to generate coefficient data
A quantization circuit 16 that quantizes the coefficient data from the DCT circuit 15 with a fixed quantization step size to generate quantized data, and a variable-length coding of the quantized data from the quantization circuit 16. , A variable length coding (VLC: Variable Length Code) circuit 17 for outputting variable length code data, and an inverse quantization circuit 18 for inversely quantizing the quantized data from the quantization circuit 16 to reproduce coefficient data.
And the coefficient data from the inverse quantization circuit 18, for example, inverse discrete cosine transform (hereinafter referred to as IDCT: Inverse Discrete C)
ID which reproduces the difference by “sine transform”
The difference between the CT circuit 20 and the IDCT circuit 20 and the motion-compensated predicted image data from the motion compensation circuit 23 are added to generate predicted image data for the next input image data, and the predicted image data is stored in the frame memory 22. And an adder circuit 21 for supplying.

As shown in FIG. 1, the second encoding circuit 40 includes a delay unit 43 for delaying the input image data.
And a frame memory 52 for storing predicted image data;
A motion compensation circuit 53 for performing motion compensation on the predicted image data read from the frame memory 52 based on the motion vector from the motion vector detection circuit 11;
3, a prediction encoding circuit 44 that predictively encodes the input image data delayed by the delay unit 43 based on the motion-compensated prediction image data, and a difference from the prediction encoding circuit 44. A DCT circuit 45 that performs DCT conversion to generate coefficient data, a quantization scale setting circuit 33 that sets a quantization step size based on an encoding rate from the encoding control circuit 30, and a coefficient data from the DCT circuit 45 A quantization circuit 46 that quantizes with the quantization step size from the quantization scale setting circuit 33 to generate quantized data, and a variable length code of the quantized data from the quantization circuit 46 to convert the variable length code data A VLC circuit 47 for outputting, a transmission buffer memory 49 for temporarily storing the variable length code data from the VLC circuit 47, and outputting the same at a constant bit rate; An inverse quantization circuit 48 to reproduce coefficient data to inverse quantization to the quantized data from the circuit 46,
The coefficient data from the inverse quantization circuit 48 is decoded, for example, I
An IDCT circuit 50 that performs DCT conversion and reproduces a difference;
An addition circuit 51 that adds the difference from the DCT circuit 50 and the motion-compensated predicted image data from the motion compensation circuit 53 to generate predicted image data for the next input image data, and supplies the predicted image data to the frame memory 52 And

In this image encoding apparatus, the first encoding circuit 10 encodes the input image data,
For example, the encoding control circuit 30 performs a predictive encoding process, a DCT transform process, a quantization process with a fixed quantization step size, and a variable length encoding process. And the total available data determined by the data capacity of the image recording medium 55 such as an optical disk, a magnetic disk, a magnetic tape, or the like, or the bit rate (transfer rate) of the transmission path. After obtaining the coding bit rate, the second coding circuit 40 performs predictive coding processing, DCT transform processing, quantization processing again on the input image data.
When performing variable length coding processing to generate variable length code data as a second bit stream, quantization is performed with a quantization step size based on the coding bit rate.

That is, in this image coding apparatus, as shown in FIG. 2, for example, in step ST1, the quantization circuit 16 of the first coding circuit 10 sets the quantization step size to, for example, 1 and sends it to the DCT circuit 15 from the DCT circuit 15. The supplied coefficient data is quantized to generate quantized data, and the counter 31 of the encoding control circuit 30 performs variable-length coding on the quantized data to obtain variable-length code data (first bit stream). Is counted for a predetermined period of time, for example, for each frame, and a generated code amount indicating the difficulty of encoding is obtained for each frame.

In step ST2, the bit rate calculation circuit 32 determines the degree of difficulty (the amount of generated code) for each frame,
Based on the total amount of usable data, an assigned code amount assigned to each frame is obtained.

In step ST3, the quantization circuit 46 of the second encoding circuit 40 quantizes the coefficient data supplied from the DCT circuit 45 with a quantization step size based on the allocated code amount, and Is generated.

Specifically, the input image data is temporarily stored in the frame memory group 12. Then, the data is read from the frame memory group 12 according to the block format as described in the related art.

The motion vector detecting circuit 11 reads out necessary image data from the frame memory group 12 in units of the above-described macroblocks, and detects a motion vector. That is, the motion vector detection circuit 11
Using the forward original image and / or the backward original image stored in 2, the motion vector of the current reference image is detected in macroblock units. Here, in detecting a motion vector, for example, a motion vector in which the sum of absolute values of differences between frames in a macroblock unit is minimized is set as the motion vector. Then, the detected motion vector is added to the motion compensation circuits 23 and 53.
The sum of the absolute values of the differences between the frames in macroblock units is supplied to the intra-frame / forward / backward / bidirectional prediction determination circuit 13.

The intra / forward / backward / bidirectional prediction determination circuit 13 determines the prediction mode of the reference block based on this value, and, based on the determined prediction mode, the intra / forward / backward prediction for each block. / Controls the prediction encoding circuit 14 to switch between bidirectional prediction.

As shown in FIG. 1, the predictive coding circuit 14 includes adders 14a, 14b, 14c and a changeover switch 14d. In the case of the bidirectional prediction mode, a difference (hereinafter referred to as difference data) of each pixel of input image data with respect to each predicted image is selected, and the selected data is supplied to the DCT circuit 15.

The DCT circuit 15 uses the two-dimensional correlation of the video signal to perform DCT conversion on the input image data or the difference data supplied from the changeover switch 14d in block units, and outputs the obtained coefficient data to the quantization circuit 16. Supply.

The quantization circuit 16 sets a constant quantization step size, for example,
The coefficient data supplied from the T circuit 15 is quantized, and the obtained quantized data is converted to the VLC circuit 17 and the inverse quantization circuit 1.
8

The VLC circuit 17 performs variable length coding on the quantized data together with the quantization step size, prediction mode, motion vector, etc., and supplies the obtained variable length code data to the coding control circuit 30 as a first bit stream. I do.

As shown in FIG. 1 described above, the encoding control circuit 30 includes a counter 31 for counting the amount of variable-length code data from the VLC circuit 17 for each predetermined time,
And a bit rate calculation circuit 32 for calculating an allocated code amount per predetermined time based on the data amount from 1 and the total amount of usable data. Then, the counter 31 counts the data amount of the first bit stream every predetermined time, for example, every frame, finds the difficulty for each frame, and supplies this difficulty to the bit rate calculation circuit 32.

The bit rate calculation circuit 32 calculates the allocated code amount allocated to each frame, that is, the average coding rate for each frame time, based on the difficulty level for each frame and the total amount of usable data. The code amount is supplied to the quantization scale setting circuit 33 of the second coding circuit 40.

More specifically, the bit rate operation circuit 32
Indicates that the total number of frames is N and the total amount of usable data is B
And then, i (i = 0,1,2 ··· N -1) th frame difficulty of the (generated code amount) and _{d i,} the assigned code amount for the i-th frame as _{b i,} the assigned code Quantity b
If is proportional to the degree of difficulty d _i to indicate _i by the following formula 1,
Data amount B is as shown in the following formula 2, obtained by adding the allocated code quantity b _i of all frames. Note that a is a constant.

[0066]

(Equation 9)

[0067] Accordingly, constant a can be obtained by the following formula 3, and substituting this constant a into the formula 1, the assigned code amount b _i for the i-th frame, it can be determined by the following equation 4.

[0068]

(Equation 10)

Thus, the bit rate operation circuit 32
For example, the frame of the picture is complex image by increasing the assigned code amount b _i, for the simple picture frame to reverse to reduce the allocated code quantity b _i.

On the other hand, the inverse quantization circuit 18 includes the quantization circuit 1
The quantization data supplied from 6 is inversely quantized with the quantization step size set to 1, and coefficient data (to which quantization distortion is added) corresponding to the output of the DCT circuit 15 is reproduced. It is supplied to the IDCT circuit 20.

The IDCT circuit 20 converts the coefficient data into IDC
T-transform and reproduce input image data corresponding to the output of the predictive coding circuit 14 in the intra-frame coding mode, and reproduce difference data in the forward / backward / bidirectional prediction mode.
It is supplied to the addition circuit 21.

In the forward / backward / bidirectional prediction mode, the addition circuit 21 is supplied with the predicted image data which has been motion-compensated from the motion compensation circuit 23, and the difference between this predicted image data and the IDCT circuit 20. By adding the data, the image data corresponding to the input image data is reproduced.

The image data reproduced in this way is stored in the frame memory 22 as predicted image data. That is, the inverse quantization circuit 18 to the addition circuit 21
Constitutes a local decoding circuit, based on the prediction mode,
The quantized data output from the quantization circuit 16 is locally decoded, and the obtained decoded image is written to the frame memory 22 as a forward predicted image or a backward predicted image. The frame memory 22 is composed of a plurality of frame memories, a bank switching of the frame memories is performed, and, for example, a single frame is output as forward predicted image data or backward predicted image data according to an image to be encoded. Is output. In the case of forward / backward / bidirectional prediction, forward predicted image data and backward predicted image data are averaged and output, for example. These prediction image data are exactly the same image data as the image data reproduced by the image decoding device described later, and the next processed image is subjected to forward / backward / bidirectional prediction coding based on this prediction image. Will be

Next, the operation of the second encoding circuit 40 will be described. The circuits other than the quantization scale setting circuit 33, the delay unit 43, the quantization circuit 46, and the transmission buffer memory 49 constituting the second encoding circuit 40 are the circuits constituting the first encoding circuit 10 described above. Since the same operation as described above is performed, the description is omitted.

The delay unit 43 delays the input image data until, for example, an encoding control signal is output from the encoding control circuit 30. Then, the predictive encoding circuit 44, DC
In the T circuit 45, the delayed input image data is subjected to a predictive encoding process and a DCT transform process according to the prediction mode supplied from the intra-frame / forward / backward / bidirectional prediction determination circuit 13 to generate coefficient data. You.

The quantization scale setting circuit 33 divides the allocated code amount for each macroblock (for example, by dividing the allocated code amount for each frame by the number of macroblocks in one frame) from the supplied allocated code amount for each frame. Then, a comparison is made between the generated code amount generated in the macroblock detected from the buffer feedback from the transmission buffer memory 49 and the allocated code amount for each macroblock. When the quantization scale setting circuit 33 approaches the coding bit rate of each frame and the average coding bit rate for each set frame time, the generated code amount in the macro block is larger than the allocated code amount for each macro block. If the quantization step size of the next macroblock is set large to suppress the generated code amount of the next macroblock, and if the generated code amount in the macroblock is smaller than the allocated code amount for each macroblock, the generated code amount , The quantization step size of the next macroblock is reduced. However, when the buffer feedback from the transmission buffer memory 49 indicates that the overflow of the transmission buffer memory 49 is close, the quantization scale setting circuit 33 does not depend on the above-described comparison result between the allocated code amount and the generated code amount. When the quantization step size is increased to suppress the overflow, and when the buffer feedback from the transmission buffer memory 49 indicates that the underflow of the transmission buffer memory 49 is near, the above-mentioned allocated code amount and generated code amount Regardless of the comparison result, the underflow is suppressed by reducing the quantization step size. In the above description, the generated code amount and the allocated code amount are compared for each macroblock, and the quantization step size is switched for each macroblock. However, the switching may be performed for each slice. In the above description, the generated code amount is detected from the amount stored in the transmission buffer memory 49.
Can also be obtained directly from the output of The quantization scale setting circuit 33 supplies the quantization step size thus set to the quantization circuit 46.

The quantization circuit 46 quantizes the coefficient data supplied from the DCT circuit 45 according to the quantization step size supplied from the above-described quantization scale setting circuit 33 to generate quantized data.

The VLC circuit 47 includes a quantization circuit 4
6, the quantization step size from the quantization scale setting circuit 33, the prediction mode from the intra / forward / backward / bidirectional prediction determination circuit 13,
Variable-length coding is performed together with the motion vector and the like from the motion vector detection circuit 11, and the obtained variable-length code data is supplied to the transmission buffer memory 49 as a second bit stream.

That is, in this image encoding apparatus, as shown in FIG. 3, for example, when image data is input via the delay unit 43 in step ST1, the process proceeds to step ST1.
In step 2, the quantization scale setting circuit 33 reads, from the encoding control circuit 30, the code amount allocated to the frame currently being encoded, and proceeds to step ST3.

In step ST3, the predictive coding circuit 44 to the VLC circuit 47 perform a predictive coding process and a DCT transform process on the image data, and quantize the coefficient data by a quantization step size based on the allocated code amount. Thereafter, variable-length coding is performed, and the process proceeds to step ST4.

In step ST4, for example, it is determined whether or not the encoding process has been completed for all frames (sequences) to which the same screen size and the same transfer rate are applied. Returns to step ST1. In this way, variable rate coding in which the coding rate is changed in frame units is realized, and even if images (frames) having complicated patterns continue, the quantization step size for these images is increased as in the conventional device. Without this, uniform high image quality can be obtained throughout.

Then, the transmission buffer memory 49 temporarily stores the variable-length code data, reads it out at a constant bit rate, and smoothes the variable-length code data to output it as a bit stream. The bit stream output from the transmission buffer memory 49 is multiplexed with, for example, an encoded audio signal, a synchronization signal, and the like, further added with an error correction code, and subjected to predetermined modulation suitable for transmission or recording. After being added, it is transmitted to an image decoding device via a transmission path, for example, or
As shown in (1), it is recorded on an image recording medium 55 composed of an optical disk, a magnetic disk, a magnetic tape or the like. That is,
In the second encoding circuit 40, for example in advance for the complex image by increasing the assigned code amount b _i, for the simple image subjected to variable rate encoding by reducing the allocated code quantity b _i Therefore, it is not necessary to apply a fixed rate of a high rate throughout the entire image in order to avoid extreme image quality degradation for an image having a complicated pattern as in the conventional apparatus, and to increase the recording time of the image recording medium 55. can do.

On the other hand, the inverse quantization circuit 48 includes the quantization circuit 4
6 is supplied to the above-described quantization circuit 4
6 is inversely quantized by the quantization step size used in
The coefficient data (to which the quantization distortion is added) corresponding to the output of the DCT circuit 45 is reproduced, and
It is supplied to the CT circuit 50. That is, the inverse quantization circuit 48 to the addition circuit 51 constituting the local decoding circuit locally decode the quantized data output from the quantization circuit 46 and use the obtained decoded image as a forward prediction image or a backward prediction image as a frame. Write to the memory 52. Frame memory 5
The image data stored in 2 is used as a predicted image for the next processed image.

By the way, in the above-described embodiment, the allocated code amount per predetermined time, that is, the average coding rate per predetermined time is obtained for each frame by using the frame as the predetermined time, but the present invention is not limited to this. It is not something to be done. For example, a so-called MPEG (Moving Picture Expert)
A GOP (Group of Picture) in a Group) may be set as a predetermined time. The above-mentioned MPEG is a so-called ISO
(International Organization for Standardization) and IEC (International Electrotechnical Commission) J
SC (S) at TC (Joint Technical Committee) 1
ub Committee) 29 is a common name for a moving picture coding method under consideration in a WG (Working Group) 11.

That is, a GOP in MPEG is composed of at least one so-called I picture and a plurality of P pictures or B pictures (non-I pictures). Specifically, for example, as shown in FIG. 4, one I picture, four P pictures in a three-picture cycle, and ten B pictures
If the encoding control circuit 3
0 calculates the assigned code amount for each GOP. Here, an I picture is an image that is coded in a field or an intra-frame, and a P picture is an image that can be predicted only from the forward direction and is coded between a field or an inter-frame. Is an image that can be predicted from the forward direction, from the backward direction, and from both directions, and is encoded between fields or between frames.

Then, in the first encoding circuit 10,
For example, as shown in FIG. 5, two consecutive pictures in a GOP are tentatively defined as an I picture and a P picture with the number of pictures constituting the GOP as a cycle, and the quantization step size is set to 1, for example. Predictive coding processing for image data of I picture and P picture, DCT
A conversion process and a variable-length encoding process are performed to generate variable-length code data, and the variable-length code data is
Supply 0. Here, two pictures are I pictures,
The P picture is used to check the complexity of the picture and the correlation between the frames. The complexity of the picture can be known from the generated code amount of the I picture. We can know the correlation. Generally, since a plurality of continuous frames have similar images, the tendency of the picture of the GOP can be seen even from the two extracted pictures.

[0087] The coding control circuit 30 is configured to count the data amount BITP _j data amount Biti _j and P picture of the I picture in each GOP, for example, as shown in the following formula 5, these data amount Biti _j, BITP _{Based on j} and the number N of P pictures constituting the GOP, a difficulty level (generated code amount) GOPd _j (j = 0, 1, 2,...) is obtained for each GOP.

[0088] Then _{GOPd j = bitI j + N ×} bitP j ··· Equation 5, the encoding control circuit 30, and the GOP for each of difficulty (amount of generated code) GOPd _j, based on the available data amount, The allocated code amount allocated to each GOP is obtained, and the allocated code amount is supplied to the second encoding circuit 40.

More specifically, the total number of GOPs is M, the total amount of usable data is B, the code amount allocated to the j-th GOP is GOPb _j , and the allocated code amount GOPb _j is expressed by the following equation (6). The total data amount B is obtained by adding the allocated code amounts GOPb _j of all the GOPs as shown in the following Expression 7. Note that a
Is a constant.

[0090]

[Equation 11]

Accordingly, the constant a can be obtained by the following equation 8, and when this constant a is substituted into the equation 6, the allocated code amount GOPb _j for the j-th GOP can be obtained by the following equation 9.

[0092]

(Equation 12)

Thus, the coding control circuit 30 increases the allocated code amount GOPb _j for a GOP containing a picture with a complicated pattern or a GOP having a low correlation between frames, for example. For a GOP that is included or has a high correlation between frames, the allocated code amount GOPb _j
Less.

Next, as shown in FIG. 6, for example, as shown in FIG.
When the image data is input through the step ST2, in step ST2, it is determined whether the currently input image data is the first picture of the GOP. If the image data is applicable, the process proceeds to step ST3, and if not, the process proceeds to step ST4.

In step ST3, the second encoding circuit 40 reads from the encoding control circuit 30 the amount of code allocated to the GOP currently being encoded, and proceeds to step ST4.

In step ST4, the second encoding circuit 40 performs a predictive encoding process and a DCT transform process on the image data, and quantizes the coefficient data with a quantization step size based on the allocated code amount. Variable length coding is performed, and the process proceeds to step ST5.

Here, the quantization scale setting circuit 33
From the supplied allocated code amount for each GOP, the allocated code amount for each frame is determined by the picture type (I
Picture, P picture, B picture), that is, the picture type shown in FIG. Specifically, the allocated code amount for the I picture is increased, the allocated code amount for the B picture is reduced, and the allocated code amount for the P picture is set in the middle. Subsequent processing of the quantization scale setting circuit 33 is the same as that of the embodiment in which the allocated code amount is obtained for each frame described above.

Next, in step ST5, it is determined whether or not the encoding process has been completed for all frames (sequences) to which the same screen size and the same transfer rate are applied. If it is, the process returns to step ST1. In this way, variable rate coding in which the coding rate is changed in GOP units is realized, and even if images (frames) having complicated patterns continue, the quantization step size for these images is increased as in the conventional apparatus. Without this, uniform high image quality can be obtained throughout. Further, in this embodiment, since the allocated code amount for each GOP is obtained based on two pictures, high-speed processing is possible as compared with the above-described embodiment. It is needless to say that the allocated code amount of each GOP may be obtained based on the data amount of all pictures in the GOP.

Note that the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, DCT is used for transform coding, but so-called strat transform, Haar transform, wavelet transform, etc. Is also good.

[0100]

As is apparent from the above description, according to the present invention, an input video signal is encoded, for example, predictive encoding, DCT
Transformation, quantization at a fixed quantization step size, and variable-length encoding to generate first encoded data, and for each predetermined time of the first encoded data, for example, for each frame or GOP, By calculating the assigned code amount for each frame or GOP based on the total amount of usable data, and encoding the input video signal at predetermined time intervals based on the assigned code amount to generate second encoded data, Variable-rate coding in which the coding rate is changed at predetermined time intervals is realized, and even if images (frames) having complicated patterns continue, the quantization step size is increased for these images as in the conventional device. Therefore, uniform high image quality can be obtained throughout.

Since the second encoded data obtained as described above has a variable rate, by recording this on an image recording medium, a limited recording capacity can be used effectively, and The recording time of the recording medium can be lengthened. Then, uniform high-quality image data can be reproduced from the image recording medium throughout.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of a main part of an image encoding device to which the present invention has been applied.

FIG. 2 is a flowchart illustrating an operation of a first encoding circuit included in the image encoding device.

FIG. 3 is a flowchart illustrating an operation of a second encoding circuit included in the image encoding device.

FIG. 4 is a diagram showing each picture for explaining the structure of a GOP in MPEG.

FIG. 5 is a diagram illustrating each picture for describing an encoding control signal for each GOP.

FIG. 6 is a flowchart for explaining an operation of a second encoding circuit forming the image encoding device.

FIG. 7 is a diagram showing an image for explaining the principle of predictive coding.

FIG. 8 is a diagram showing an image for explaining the principle of motion compensated prediction coding.

FIG. 9 is a block diagram illustrating a configuration of an image encoding device and an image decoding device.

FIG. 10 is a diagram illustrating a configuration of a macroblock and a slice.

FIG. 11 is a block diagram showing a circuit configuration of a conventional encoder.

FIG. 12 is a block diagram showing a circuit configuration of a conventional decoder.

[Description of Signs] 10 first encoding circuit, 11 motion vector detecting circuit, 12 frame memory group, 13 intra / forward / backward / bidirectional prediction determining circuit, 14 predictive encoding circuit,
15 DCT circuit 15, 16 Quantization circuit, 17 VL
C circuit, 18 inverse quantization circuit, 20 IDCT circuit, 2
1 addition circuit, 22 frame memory, 23 motion compensation circuit, 30 encoding control circuit, 31 counter, 32 bit rate operation circuit, 33 quantization scale setting circuit,
40 second encoding circuit, 43 delay unit, 44 predictive encoding circuit, 45 DCT circuit, 46 quantization circuit, 47
VLC circuit, 48 inverse quantization circuit, 49 transmission buffer memory, 50 IDCT circuit, 51 addition circuit, 52
Frame memory, 53 Motion compensation circuit, 55 Image recording medium

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 7/30 H04N 7/133 Z

Claims (27)

[Claims] An encoding method comprising: encoding at least a part of an input video signal to generate first encoded data; and generating the first encoded data based on a data amount of the first encoded data at predetermined time intervals and a total usable data amount. An image coding method comprising: obtaining a coding rate for each predetermined time; and coding the input video signal for each predetermined time based on the coding rate to generate second coded data. 2. The image encoding method according to claim 1, wherein said first encoded data is generated by quantizing at least a part of said input video signal with a fixed quantization step size. 3. The image encoding apparatus according to claim 1, wherein the total amount of usable data is proportionally distributed according to the amount of data at each of the predetermined times to determine an encoding rate at each of the predetermined times. Method. 4. A first predictive coding and / or a predetermined transform coding is performed on at least a part of an input video signal to generate first coefficient data, and the first coefficient data is subjected to a predetermined quantization step. Quantizing by size to generate first quantized data; Variable-length coding the first quantized data to generate a first bit stream; Calculating a coding rate for each predetermined time based on the total amount of data; performing the predetermined predictive coding and / or the predetermined transform coding on the input video signal to generate second coefficient data; The second coefficient data is quantized with a quantization step size based on each encoding rate to generate second quantized data, and the second quantized data is subjected to variable length encoding to generate a second bit. story Picture coding method and generating a. 5. The image according to claim 4, wherein the coding rate is obtained for each frame based on a data amount for each frame and a total amount of usable data in the first bit stream. Encoding method. 6. The coding rate is determined for each GOP based on at least a part of the data amount of each GOP including a plurality of frames in the first bit stream and a total amount of usable data. The image encoding method according to claim 4, wherein 7. The method according to claim 7, wherein the G is based on a data amount for an intra-coded image and a forward prediction-coded image in the GOP.
7. The image coding method according to claim 6, wherein a coding rate for each OP is obtained. 8. The coding rate for each predetermined time is obtained by proportionally distributing the total amount of usable data according to the data amount of the first bit stream for each predetermined time. 5. The image coding method according to 4. 9. A difficulty level of encoding is determined for each predetermined image unit of the input video signal, and an encoding rate is set for each predetermined image unit based on the difficulty level of encoding and the total amount of usable data. An image coding method, wherein the input video signal is coded so that the coding rate of each image unit matches the set coding rate of each image unit. 10. The image encoding method according to claim 9, wherein said predetermined image unit is a frame. 11. The image encoding method according to claim 9, wherein said predetermined image unit is a GOP including a plurality of frames. 12. A coefficient data is generated by subjecting at least a part of the input video signal to a predetermined predictive coding and / or a predetermined transform coding, and the coefficient data is quantized with a fixed quantization step size. 10. The image encoding method according to claim 9, wherein the degree of difficulty of the encoding is obtained. 13. A first encoding unit that encodes at least a part of an input video signal to generate first encoded data, and a first encoding unit that outputs the first encoded data from the first encoding unit. Coding control means for obtaining the coding rate for each predetermined time based on the data amount per time and the total amount of usable data; and the predetermined time based on the coding rate for each predetermined time from the coding control means. A second encoding unit that encodes the input video signal to generate second encoded data every time. 14. The image code according to claim 13, wherein said first encoding means includes a quantization means for quantizing at least a part of said input video signal with a fixed quantization step size. Device. 15. The coding control means according to claim 1, wherein said coding control means obtains the coding rate for each predetermined time by proportionally distributing the total amount of usable data in accordance with the data amount for each predetermined time. Item 14. The image encoding device according to Item 13. 16. A first predictive coding and / or a predetermined transform coding on at least a part of an input video signal to perform a first
A first encoding unit for generating coefficient data of the first type, and a first encoding unit for generating first quantized data by quantizing the first coefficient data from the first encoding unit with a fixed quantization step size. A first variable length coding unit that performs variable length coding on the quantized data from the first quantization unit to generate a first bit stream; and a first variable length coding unit. Coding control means for obtaining a coding rate for each predetermined time based on the data amount of the first bit stream from the means and the total amount of usable data; and the predetermined predictive coding and / or A second encoding unit that performs a predetermined conversion encoding to generate second coefficient data; and the second encoding unit generates a second coefficient data by a quantization step size based on an encoding rate for each predetermined time from the encoding control unit. From the encoding means A second quantizing means for quantizing the coefficient data of No. 2 to generate second quantized data; and a second bit for performing variable length encoding on the second quantized data from the second quantizing means. An image encoding apparatus, comprising: a second variable-length encoding unit that generates a stream. 17. The coding control means for calculating the coding rate for each frame based on a data amount for each frame and a total amount of usable data in the first bit stream. 17. The image coding apparatus according to claim 16, wherein: 18. The coding control means for each GOP based on at least a part of a data amount of each GOP including a plurality of frames in the first bit stream and a total amount of usable data. 17. The image encoding apparatus according to claim 16, wherein a rate is obtained. 19. The coding control means for calculating the coding rate for each GOP based on the amount of data for an intra-picture coded picture and a forward prediction coded picture in the GOP. 19. The image encoding device according to 18. 20. The encoding control means obtains an encoding rate for each predetermined time by proportionally distributing the total amount of usable data in accordance with an amount of data of the first bit stream for each predetermined time. 17. The image coding apparatus according to claim 16, wherein: 21. A difficulty calculating means for calculating a coding difficulty for each predetermined image unit of the input video signal, and the coding difficulty from the difficulty calculating means and a total amount of usable data. Encoding rate setting means for setting an encoding rate for each predetermined image unit; and an encoding rate for each image unit set by the encoding rate setting means. And an encoding means for encoding the input video signal. 22. The apparatus according to claim 2, wherein the difficulty calculating means calculates the encoding difficulty for each frame.
2. The image encoding device according to 1. 23. The image coding apparatus according to claim 21, wherein said difficulty calculation means calculates the coding difficulty for each GOP including a plurality of frames. 24. The difficulty level calculating means generates coefficient data by performing a predetermined predictive coding and / or a predetermined transform coding on at least a part of the input video signal, and converts the coefficient data into a fixed value. 22. The image encoding apparatus according to claim 21, wherein the difficulty of the encoding is obtained by quantizing with a quantization step size. 25. Encoding at least a part of an input video signal to generate first encoded data, and based on a data amount of the first encoded data at predetermined time intervals and a total usable data amount. An image recording medium, wherein an encoding rate for each predetermined time is obtained, and a second bit stream obtained by encoding the input video signal every predetermined time based on the encoding rate is recorded. . 26. A first predictive coding and / or a predetermined transform coding performed on at least a part of an input video signal to perform a first
Is generated, and the first coefficient data is quantized with a fixed quantization step size to generate first quantized data. The first quantized data is subjected to variable-length coding to generate a first quantized data. Generating a bit stream; determining an encoding rate for each predetermined time based on the data amount of the first bit stream and the total amount of usable data; and performing the predetermined predictive encoding and / or the predetermined To generate second coefficient data, and quantize the second coefficient data with a quantization step size based on the coding rate for each predetermined time to generate second quantized data. An image recording medium characterized by recording a second bit stream obtained by variable-length encoding the second quantized data. 27. A difficulty level of encoding is determined for each predetermined image unit of an input video signal, and an encoding rate is set for each predetermined image unit based on the difficulty level of encoding and the total amount of usable data. Then, encoded data obtained by encoding the input video signal so that the encoding rate of each image unit matches the encoding rate of each set image unit is recorded. Image recording medium.