JPH11234549A - Automatic focus device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focus circuit that conducts automatic focus control with high accuracy by eliminating middle and high frequency components undesired for the automatic focus control even in the case of an image including an object with high luminance whose focusing is difficult. SOLUTION: A middle and high frequency component signal is obtained by a middle and high frequency component detection circuit 5 from a video signal from an image pickup element, a high luminance detection signal at a level higher than a setting level is obtained by a high luminance detection circuit 7, and an oblique discrimination signal higher than a set oblique level is obtained by an oblique detection circuit 8 and an oblique discrimination circuit 9. A signal obtained by shutting out the middle and high frequency component signal accumulated or integrated by an integration circuit 12 is used to control the focus by allowing a variable delay circuit 10 to delay the high luminance detection signal and the slope discrimination signal by a delay level calculated and set from the signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auto-focusing device, and more particularly, to a method for detecting a mid-high frequency component of a video signal from an image pickup device such as a video camera, and adjusting the focus of a lens so that the amplitude thereof is maximized. The present invention relates to an autofocus device that controls

[0002]

2. Description of the Related Art Conventionally, in this type of autofocus apparatus, when detecting a middle to high frequency component of a video signal, a high brightness is used so that focusing accuracy is not deteriorated even if a high brightness subject is included on a screen. The middle and high frequency components at the time of part detection are removed, and a control operation of focusing of the lens is performed. A conventional example is disclosed in Japanese Patent No. 2529211.

FIG. 4 is a block diagram for explaining an autofocus apparatus according to a conventional example. In FIG. 4, reference numeral 41 denotes a lens, and 42 denotes an electric signal representing a subject image formed on a light receiving surface by the lens 41. This is an image sensor that converts the image data into an image. 43 is a preamplifier for amplifying the electric signal, 44 is a preamplifier 4
A process circuit for performing various processes on the output signal of 3 to produce a television signal; 45, a synchronizing signal generator for generating a synchronizing signal, a blanking signal, and the like; and 46, an image sensor driving circuit for driving the image sensor. Reference numeral 47 denotes a high frequency component detection circuit for detecting a high frequency component from the output video signal of the preamplifier 43. 48 is a reference frequency generator that supplies a reference frequency to a synchronous detection circuit 50 and a motor drive circuit 51; 49 is a reference frequency component that detects a reference frequency component included in the high frequency component obtained by the high frequency component detection circuit 47 The detection circuit 50 performs synchronous detection of the reference frequency component detected by the reference frequency component detection circuit 49 at the reference frequency, and outputs the motor 52 through the motor drive circuit 51 with the obtained synchronous detection output.
Is a synchronous detection circuit that drives. 53 is a preamplifier 43
Is a comparator for detecting that the amplitude of the video signal obtained from the signal exceeds the detection level given from the detection level generator 55. Reference numeral 54 denotes a gate circuit that cuts off the output signal of the high frequency component detection circuit 47 by the output of the comparator 53 and cuts off the output signal of the high frequency component detection circuit 47 so that the signal is not input to the reference frequency component detection circuit 49. , 55 are detection level generators that output one of two different detection levels according to the output of the comparator 53.

FIGS. 5 and 6 are diagrams for explaining the operation of the autofocus apparatus shown in FIG.
Reference numeral 6 denotes a video signal, and 57 denotes a detection level. The comparator 53 in FIG. 4 compares the amplitude of the video signal 56 output from the preamplifier 43 with the detection level 57 and outputs the result as a comparator output 58. Output from the comparator 53. When the comparator 53 detects a high luminance portion exceeding the detection level in the video signal, the gate circuit 54 cuts off the high frequency component signal so that no signal is input to the reference frequency component detection circuit 49. The detection level generator 55 outputs the detection level A when the comparator 53 does not detect the high luminance portion, and outputs the detection level B slightly lower than the detection level A when the comparator 53 detects the high luminance portion. Therefore, the detection level 57 has a hysteresis characteristic as shown in FIG.

With such a configuration, a high-frequency component signal included in a video signal between the high-luminance portion detected by the comparator 53 can be cut off. Further, even if the video signal contains a noise component as shown in FIG. 6 and the video signal exceeds the detection level A many times, the detection levels have hysteresis characteristics. In the case of a video signal containing noise fluctuating between levels, the output of the comparator becomes as shown by 60 in FIG. 6 due to this hysteresis characteristic, and the output of the comparator is less affected by noise. As described above, the conventional autofocus device operates with the desired focusing accuracy by setting the detection level of the comparator 53 to an appropriate value.

[0006]

However, in the above-mentioned prior art, although there is a luminance difference, in the case of a video signal of a high-luminance object or the like as a whole, the signal as a whole exceeds the set detection level, and the lens Since all the middle and high frequency components required for focusing are cut off, focusing becomes difficult. In a video signal in which a high-luminance object is present in a part of the image, such as a light source, a mid-high frequency component irrelevant to the focus of the lens is detected at the boundary between the high-luminance part and the other part. Therefore, even if a portion exceeding the set detection level is cut off, the middle and high frequency components irrelevant to the focusing of the lower lens are used for focus control without being cut off. Therefore, when there is a high-luminance subject in a part of the video signal, there is no difference between the size of the mid-high frequency component at the time of focusing of the lens and the size of the mid-high frequency component at the time of blurring. Accuracy will be reduced. Means for Solving the Problems The present invention has been made in view of the above situation, and enables a normal operation to be performed on a video signal in which a high-luminance subject is present in a part of a video in which a problem has occurred in the related art. It is an object of the present invention to provide an auto-focusing device that takes the above-mentioned measures.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a medium-high frequency component detection circuit for detecting a medium-high frequency component of a video signal, and a video signal amplitude setting circuit. A high-brightness detection circuit for detecting that the level is greater than a certain detection level, a gradient detection circuit for detecting a gradient from a video signal by differentiation or a difference, and a gradient detected by the gradient detection circuit being greater than a predetermined level. A tilt determination circuit that detects that, a variable delay circuit that delays the high brightness detection signal output from the high brightness detection circuit and the tilt determination signal output from the tilt determination circuit by a delay level set based on those signals, A fixed delay circuit for delaying the video signal or the mid-high frequency component signal from the mid-high frequency component detection circuit for a predetermined time; An integrating circuit for integrating or integrating the signals; a focus control device for moving the focal point of the lens so that the output from the integrating circuit is maximized; and a predetermined control circuit. An auto-focus device is characterized in that it is configured to block the input of the frequency component signal to the integrating circuit.

With the above-configured auto-focus device, when the mid-high frequency component signal is detected by the mid-high frequency component detection circuit from the video signal from the image sensor, the signal is higher than a certain detection level set by the high luminance detection circuit. A high-brightness detection signal is obtained based on the high-brightness detection signal and the high-brightness detection signal from the high-brightness detection signal and the high-intensity determination signal by a variable delay circuit. By intercepting the input of the mid-high frequency component signal to the integrating circuit by the gate signal obtained by delaying the predetermined delay time, the entire high-luminance subject was photographed from the mid-high frequency component detection circuit. To remove mid- and high-frequency components that are unnecessary for lens focusing that occur when there is a high-brightness subject in time or part of the image Ri By obtain high integration result accuracy even when a high luminance object, in which to obtain high focusing accuracy autofocus device.

[0009] The invention of each claim forms the following technical means. The invention according to claim 1 is an autofocus device that detects a middle-high frequency component of a video signal from an image sensor and controls a focusing lens so that the middle-high frequency component is maximized. A mid-high frequency component detection circuit that detects a mid-high frequency component, a high luminance detection circuit that detects that the amplitude of the video signal is greater than a set detection level, and a tilt detection circuit that detects a tilt of the video signal. A slope determination circuit for detecting that the slope detected by the slope detection circuit is greater than a certain level set as a slope value, and a high brightness detection circuit based on the high brightness detection circuit output and the slope determination circuit output. A variable delay circuit that delays the output edge signal by a predetermined time to generate a gate signal; and a fixed delay circuit that delays the output of the middle and high frequency component detection circuit by a predetermined time. A delay circuit, a gate circuit that passes the output of the fixed delay circuit by a gate signal from the variable delay circuit, and an integration circuit that integrates or integrates the output of the gate circuit. The focus control unit controls the focus lens so that the focus lens becomes maximum.

According to a second aspect of the present invention, in the first aspect, the variable delay circuit provides a pair of delay times for forming a predetermined gate time interval for each edge of the output of the high luminance detection circuit. Thus, the gate signal is generated.

According to a third aspect of the present invention, in the second aspect of the present invention, different gate start times and different time intervals are provided as the gate time intervals depending on whether the edge rises or falls. is there.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, different gate start times and different time intervals are provided as the gate time intervals in accordance with the level set as the slope value in the slope determination circuit. It is characterized by the following.

[0013]

FIG. 1 is a block diagram for explaining an embodiment of an autofocus circuit used in an autofocus apparatus according to the present invention. In FIG. This is an image sensor that converts a subject to an electric signal. 3 is a preamplifier for amplifying the electric signal, 4 is a process circuit for converting the output signal of the preamplifier 3 into a television signal, and 5 is a mid-high frequency detecting a mid-high frequency component from an output video signal of the process circuit 4. A fixed delay circuit 6 for delaying the output of the middle and high frequency component detection circuit 5 for a predetermined time (the fixed delay circuit 6 may be provided before or inside the middle and high frequency component detection circuit 5); Is a high brightness detection circuit for detecting that the amplitude of the output video signal of the process circuit 4 exceeds a set detection level, 8 is a tilt detection circuit for detecting the tilt of the output video signal of the process circuit 4, and 9 is a tilt detection A slope determination circuit 10 for comparing the slope output of the circuit 8 with a certain level set as a slope value, and a signal 10 from the high luminance detection circuit 7 and the signal from the slope determination circuit 9 based on those signals. Variable delay circuit for delaying only delay level set you are,
Reference numeral 11 denotes a circuit for intercepting the middle and high frequency component signal from the middle and high frequency component detection circuit 5 delayed by a fixed time by the fixed delay circuit 6 by the output of the variable delay circuit 10, and
2, a gate circuit for preventing the input to 2; an integration circuit for integrating or integrating the middle and high frequency component signals output from the middle and high frequency component detection circuit 5; By moving the motor 15 through the motor drive circuit 14, the lens 1
Is a focus control device that controls to be in focus.

Next, the operation of the autofocus circuit shown in FIG. 1 will be described in more detail with reference to FIGS. FIG. 2 is a waveform diagram for explaining an example of the operation in the case of defocusing, and the circuit operation will be described below with reference to FIG. FIG. 2 shows a high-brightness detection signal 23, which is the output of the high-brightness detection circuit 7 in FIG. Is a signal waveform output as a result of the comparison. Further, the inclination detection circuit 8 differentiates the amplitude of the video signal 21 output from the process circuit 4,
Alternatively, an output of detecting the inclination of the video signal 21 as the difference between the amplitudes of the two points separated by the time Δt is input to the inclination determination circuit 9. The inclination determination circuit 9 compares the signal from the inclination detection circuit 8 with a certain level set as the inclination value, and compares the result with the inclination determination signal 2.
Output as 4. The variable delay circuit 10 creates a gate signal 25 from the high luminance detection signal 23 and the inclination determination signal 24.

The gate circuit 11 includes a variable delay circuit 10
FIG. 2 shows a block diagram of FIG. 2 in which a signal unnecessary for focusing of the lens is blocked out of the middle and high frequency component signals detected by the middle and high frequency component detection circuit 5 and delayed by the fixed delay circuit 6 for a predetermined time by the gate signal 25 from The middle / high frequency component signal 26 shown is output to the integrating circuit 12. Here, the high luminance detection circuit 7 has two detection levels, a detection level A and a detection level B, as shown in FIG. 2, and detects the detection level A when no high luminance part is detected, and The detection level B may be output to provide a hysteresis characteristic. Further, the middle and high frequency component detection circuit 5 may be configured by a band-pass filter, a high-pass filter, or the like.

The variable delay circuit 10 generates a gate signal 25
As shown in FIG. 2, an example of the operation for outputting the gate signal 25 is to generate the gate signal 25 in accordance with the state of the inclination determination signal 24 at the time of the rising or falling edge of the high luminance detection signal 23. Here, when the inclination determination signal 24 exists at the time of the edge (the inclination determination signal 24 indicates that the change of the video signal 21 is larger than a certain level set as the inclination value, as described above), the high luminance detection is performed. A gate signal relating to each edge is generated by setting a delay time from the edge of the signal 23 to the delay levels A and B. Specifically, the gate signal after the delay level A has passed from the edge of the high luminance detection signal 23 is H, and the gate signal after the delay level B has passed is L. This delay level A and delay level B
Depends on the rising or falling state of the high-brightness detection signal 23 so that the gate circuit 11 can sufficiently remove the middle and high frequency component signals unnecessary for lens focusing from the high-brightness detection signal 23 and the inclination determination signal 24. It can be appropriately selected and set.

FIG. 3 shows the waveforms of the respective signals at the time of focusing. A video signal 27 containing more middle and high frequency components than the video signal 21 of FIG.
The high luminance detection circuit 7 compares the amplitude of the video signal 27 with the set detection level 22, and outputs a high luminance detection signal 28. The tilt detection circuit 8 and the tilt determination circuit 9 output a tilt determination signal 29 from the video signal 27, and the variable delay circuit 10 outputs a gate signal 30 from the high luminance detection signal 28 and the tilt determination signal 29. From the video signal 27,
A middle-high frequency component signal detected by the middle-high frequency component detection circuit 5 and delayed by a fixed value by the fixed delay circuit 6 is output, passes through the gate circuit 11, and a middle-high frequency component signal 31 is output. This mid-high frequency component signal 31
Is that the video signal 27 has more middle and high frequency components than the middle and high frequency component signal 26 by an amount corresponding to the fact that the video signal 27 has more middle and high frequency components than the video signal 21.

When the middle-high frequency component detection circuit 5 is formed of a band-pass filter or a high-pass filter, a large middle-high frequency component signal is output when there is a steep amplitude change like the video signal 21. When a high-luminance subject is photographed or when a part of the video is a high-luminance subject, a mid-high frequency component signal having a large boundary is output. These mid-high frequency component signals are output in the same way as the out-of-focus video signal as shown in FIG. 2 or the in-focus video signal as shown in FIG. In this case, the difference between the results is small, and it is difficult for the focus control device 13 to determine whether or not the focus is achieved.

Even when the middle and high frequency component signals are generated, the inclination of the video signal is sufficiently large.
As a result, it is possible to remove a middle and high frequency component signal unnecessary for focusing of the lens by confirming the signal together with the high luminance detection signal 23. As described above, according to the present embodiment, when the video signal exceeds a certain amplitude value and the gradient is steep, the mid-high frequency component signal is cut off.
Since the middle and high frequency components can be detected in other portions, an autofocus circuit with high focusing accuracy can be provided.

[0020]

According to the first aspect of the present invention, according to the auto-focusing device of the present invention, the middle-high frequency component signal unnecessary for the auto-focus control generated by the middle-high frequency component detecting circuit based on the high luminance signal is eliminated. Can be removed. As a result, although there is a luminance difference that is difficult to focus in the conventional method, the focusing accuracy is improved even for an image including a high-luminance subject or a high-luminance subject in a part such as a light source as a whole.

Effects corresponding to the second to fourth aspects: In addition to the effects corresponding to the first aspect, it is possible to provide an effective means as a concrete means for generating a gate signal. As a result, a more accurate focusing result can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an autofocus circuit used in an autofocus device according to the present invention.

FIG. 2 is a waveform diagram for explaining an operation of the autofocus apparatus according to the present invention at the time of defocusing.

FIG. 3 is a waveform chart for explaining an operation at the time of focusing of an autofocus device according to the present invention.

FIG. 4 is a block diagram illustrating a configuration example of a conventional autofocus device.

FIG. 5 is a waveform chart for explaining an operation of the conventional autofocus device shown in FIG. 4 when noise is small.

FIG. 6 is a waveform chart for explaining an operation of the conventional autofocus apparatus shown in FIG. 4 when there is a lot of noise.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lens, 2 ... Image sensor, 3 ... Preamplifier, 4 ... Process circuit, 5 ... Mid-high frequency component detection circuit, 6 ... Fixed delay circuit, 7 ... High brightness detection circuit, 8 ... Tilt detection circuit,
9: tilt determination circuit, 10: variable delay circuit, 11: gate circuit, 12: integrating circuit, 13: focus control circuit, 14
... Motor drive circuit, 15 ... Motor, 21 ... Video signal, 2
2: detection level, 23: high brightness detection signal, 24: tilt determination signal, 25: gate signal, 26: middle and high frequency component signal, 27: video signal, 28: high brightness detection signal, 29: tilt determination signal, 30 ... Gate signal, 31 ... Mid-high frequency component signal, 41 ... Lens, 42 ... Image sensor, 43 ... Preamplifier, 44 ... Process circuit, 45 ... Synchronous signal generator, 4
Reference numeral 6 denotes an image sensor driving circuit, 47 denotes a high frequency component detection circuit, 48 denotes a reference frequency generator, 49 denotes a reference frequency component detection circuit, 50 denotes a synchronous detection circuit, and 51 denotes a motor driving circuit.
52: motor, 53: comparator, 54: gate circuit, 55
... detection level generator, 56 ... video signal, 57 ... detection level, 58 ... comparator output, 59 ... video signal, 60 ... comparator output.

Claims (4)

[Claims] 1. An auto-focusing device for detecting a middle-high frequency component of a video signal from an image sensor and controlling a focusing lens so that the middle-high frequency component is maximized. A middle-high frequency component detection circuit for detecting a frequency component, a high luminance detection circuit for detecting that the amplitude of the video signal is larger than a set detection level, an inclination detection circuit for detecting an inclination of the video signal, A slope determination circuit that detects that the slope detected by the slope detection circuit is greater than a certain level set as a slope value, and an output of the high brightness detection circuit based on the high brightness detection circuit output and the slope determination circuit output. A variable delay circuit for delaying the edge signal for a predetermined time to generate a gate signal, and a fixed delay for delaying the output of the mid-high frequency component detection circuit for a predetermined time A gate circuit for passing the output of the fixed delay circuit by a gate signal from the variable delay circuit, and an integrating circuit for integrating or integrating the output of the gate circuit. An autofocus device in which a focus lens is controlled by focus control means. 2. The variable delay circuit according to claim 1, wherein the gate signal is generated by giving a pair of delay times for forming a predetermined gate time interval to each edge of the output of the high luminance detection circuit. The auto-focusing device according to claim 1. 3. The autofocus apparatus according to claim 2, wherein different gate start times and time intervals are provided as said gate time intervals depending on whether said edge rises or falls. 4. The autofocus according to claim 2, wherein a different gate start time and a different time interval are provided as the gate time interval according to a level set as an inclination value in the inclination determination circuit. apparatus.