JPS5925549B2 - Image quality improvement device for color television receivers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for improving the image quality of colored image portions of color television images, and is particularly designed to better reproduce fine images in colored portions. .

FIG. 1 is a block diagram showing a part of a conventional color television receiver.

In the figure, the 1, F, signal (intermediate frequency signal) is detected by a video detector 1, and is detected by a luminance signal amplifier 2 and a band increaser.
It is supplied to the width gauge 3. The band amplifier 3 takes out the carrier color signal included in the composite color video signal, amplifies it, and supplies it to three color difference signal demodulators 4, 5, and 6. The color difference signal demodulators 4, 5, and 6 demodulate the carrier color signal to obtain three types of color difference signals (R-Y, G-Y, and B9-Y), which are then sent to the three adders 1, 8, and 9. supply to. The adders 7, 8, and 9 add the color difference signals supplied to each adder and the luminance signal amplifier 2.
By adding the transmitted luminance signals, three types of primary color signals 5 are created, and these are supplied to the picture tube 10.

In the conventional color television receiver as described above, the bandwidth of the color difference signal (for example, the output of the color difference signal demodulator 4) is
It is considerably narrower than the bandwidth of the luminance signal transmitted from the luminance signal amplifier 2. For example, in a normal NTSC color television receiver, the luminance signal contains frequency components from 0Hz to 3MHz, while the color difference signal contains frequency components of at most 500K.
It only contains frequency components up to Hz. Therefore, in colored image parts, the image is mainly composed of narrow band color difference signals, resulting in a blurred image with low sharpness.
Conventionally, as a method to improve the above drawbacks, for example, Tomimoto,
Paper by Nagaoka, Sasaki et al. “Method for improving color reproduction of color receivers” (Television Society Journal, Vol. 31, No. 8, 19)
1977, P. 662~P. 667) has been proposed.

This method creates a threshold signal proportional to the luminance signal. The color difference signal exceeding the threshold value is suppressed, and part of the luminance signal is mixed into the high level color difference signal, so the resolution of the colored image portion is improved. However, in the above method, only a part of the color difference signal is removed by using a wideband luminance signal, and the color difference signal after processing does not become higher than the color difference signal level before processing.

Therefore, there is a limit to the improvement of resolution, and when an attempt is made to increase the improvement effect, there is a problem in that the direct current color difference signal component decreases and the image becomes darker. In order to solve such problems, the present invention actively mixes the high frequency components of the luminance signal when the color difference signal is above a certain level.
The resolution of the colored image portion is significantly improved.

The present invention will be explained in detail below.

FIG. 2 is a block diagram representing one embodiment of the present invention.

In the figure, a color difference signal source 11 generates a color difference signal, and may be any one of the color difference signal demodulators 4, 5, and 6 shown in FIG. The luminance signal source 12 generates a luminance signal, and may be the luminance signal amplifier 2 shown in FIG. A color difference signal is supplied from the color difference signal source 11 to the nonlinear transmission circuit 13, which imparts nonlinear transmission characteristics to the color difference signal and then outputs it as a gain control signal. High frequency extraction circuit 1
4 extracts the high frequency component of the luminance signal supplied from the luminance signal source 12 and outputs it. The variable gain amplifier 15 is connected to the high frequency extraction circuit 14 and the nonlinear transmission circuit 13, and controls the gain for the high frequency component of the luminance signal using a gain control signal outputted from the nonlinear transmission circuit 13.

The high frequency component whose gain has been controlled is then supplied as a correction signal to the adding device 16, where it is added to the color difference signal and the luminance signal, and is used for video display. Nonlinear transmission circuit 13
The transmission characteristics are limited only by the fact that an appropriate correction signal must be output from the variable gain amplifier 15 when the correction signal is required, and should not be limited by other matters.

The high frequency extraction circuit 14 may be any circuit that substantially extracts high frequency components of the luminance signal, and is not limited to a simple high frequency filter.

Further, the addition device 16 is an addition device in a broad sense in the sense of combining images, and is not limited to a simple electronic circuit, but also includes, for example, combination in an electron gun of a picture tube or in the light emission stage.

According to this embodiment, the more the narrow-band color difference signal overlaps with the wide-band luminance signal and reduces the resolution of the colored image portion, the larger the correction signal is transmitted to the adding device 16 to improve the resolution. . FIG. 3 is a block diagram showing a more detailed embodiment of the invention.

Blocks with the same reference numerals as in FIG. 2 represent the same components. In FIG. 3, the nonlinear transmission circuit 13 is connected to the bias source 1.
7 and 18, diodes 20 and 21, and a resistor 19. Through these operations, a gain control signal for controlling the intensity of the correction signal is created from the color difference signal. That is, the color difference signal limiter 25, which is composed of the bias source 18 and the diode 21, operates to suppress components of a specific level or higher in the color difference signal supplied from the color difference signal source 11. 17 and diode 20
This circuit operates to suppress components below a specific level in the color difference signal.

Therefore, the output characteristics of the nonlinear transmission circuit 13 can take various forms depending on the DC via input voltage and output impedance of the bias sources 17 and 18. Figure 4 A, B, C, D, E
, F are examples of the above input/output special conditions. This figure has been drawn based on the following assumptions due to the display conditions. , the scope of the present invention is not limited to such assumptions. (1) The horizontal axis represents the color difference signal input level.

The extremes and zero level of the color difference signal indicate the extremes and zero level on the video information, and do not necessarily match the voltage on the circuit. (2) The vertical axis represents the gain control signal.

It is assumed that the variable gain amplifier 15 has a positive gain when a positive gain control signal is supplied, and the gain increases monotonically as the gain control signal increases. Further, it is assumed that when a zero level gain control signal is supplied, the gain is substantially zero. The characteristics of the effects of each of the input/output features shown in A to F of FIG. 4 are explained as follows.

When the color difference signal is negative, no correction signal is generated, and when it is positive, a correction signal is generated depending on the magnitude.

That is, when the color difference signal becomes positive, the color difference signal covers up the luminance signal on the screen, so at this time a correction signal is generated to restore the lost fine image portion. (B) The correction signal is generated only when the color difference signal is positive, which is the same as in case A, but the gain control signal is limited to prevent overcorrection when a large positive color difference signal appears. .

(C) When the color difference signal is positive, the same operation as in case A is performed, but when the color difference signal is negative, a correction signal with a weak opposite polarity is generated.

Normally, it is effective to implement the present invention with respect to a plurality of color difference signals, but the special case in the case of C is that the correction signal related to the color difference signal of other positive polarity has the effect of reducing undesirable coloring that occurs on the screen. There is. (D) A correction signal is generated when the color difference signal has a value equal to or higher than a specific positive level.

With this special feature, the effect can be limited to only the image portions that are darker than a certain level. (E) The purpose of the effect is the same as in case B, but operates to gradually reduce the increase in the amount of correction as the positive color difference signal increases.

(g) The purpose of the effect is the same as in case C, but the correction signal on the negative side is gradually increased.

Note that in all special cases A to F, the gain control signal is set to zero for the color difference signal at zero level, but this is to prevent unnecessary coloring from occurring in the monochrome image.

As above, regarding the input/output characteristics of the nonlinear transmission circuit shown in Figure 3,
Although the present invention has been described using several examples, the present invention is not limited to these examples, and may be applied to non-standard methods such as creating a gain control signal that should generate a sufficient correction signal for a large error color difference signal. All linear transmission circuits are included in the present invention.

In the embodiment shown in FIG. 3, the high frequency extraction circuit 14 includes a high frequency filter 22, a base clip circuit 23, a limiter 24,
It is made up of.

The luminance signal output from the luminance signal source 12 is supplied to a high-pass filter 22, where high frequency components of the luminance signal are separated. This high frequency component is supplied to a base clip circuit 23, where signals within a specific range including zero level are removed. This operation removes noise contained in high frequency components. The high frequency components from which noise has been removed are supplied to the limiter 24, where signals with excessive amplitude are
After its amplitude is limited, it is transmitted to variable gain amplifier 15. FIG. 5 shows an example of waveforms of each part of the high frequency extraction circuit 14 described above. In the figure, A is the luminance signal input, B is the output of the high-pass filter 22, C is the output of the base clip circuit 23, and D is the output of the limiter 24. Note that the base clip circuit 23 and limiter 24 are means for implementing the present invention more effectively, and sufficient effects can be obtained even if the high frequency extraction circuit 14 is composed of only the high frequency filter 22.
The variable gain amplifier 15 shown in FIG. 3 amplifies the output signal of the high frequency extraction circuit 14, and its gain is controlled by the above-mentioned control signal. FIG. 6 is a signal waveform diagram for explaining the effects of the present invention.

In this figure, the waveforms of each part are shown as a to f for three cases where the relationship between the luminance signal and the color difference signal is I, . Further, the special characteristics of the nonlinear transmission circuit 13 are assumed to be those shown in FIG. 4A. A in FIG. 6 is a color difference signal input, where I is a positive polarity, I is a negative polarity, and I is a zero polarity. b is a luminance signal input, and has the same waveform as I, . C is a high frequency component of the luminance signal, and also has the same waveform as I, . d
is the output waveform of the non-linear transmission circuit 13, in which only the positive portion of the color difference signal shown in a is output. e is the output waveform of the variable gain amplifier 15, that is, a correction signal. Since the correction signal is obtained by controlling the amplification gain for the waveform c using the waveform d, the color difference signal has a positive polarity I
The correction signal appears only during this period. The correction signal e is added to the color difference signal a to become a signal shown in f. Comparing this signal shown in f with the original color difference signal a, it can be seen that the resolution has been improved in the positive portion of the color difference signal. The reason why the correction is mainly performed on the positive side of the color difference signal is as follows. That is, in general, the chromatic brightness of colored image parts is not only transmitted from the brightness channel;
It is also transmitted from the chrominance channel, and especially for highly saturated colors, the luminance component transmitted from the chrominance channel is much larger than the luminance component transmitted from the luminance channel.
Moreover, most of the luminance components transmitted from the color difference channels are transmitted from the color difference signal channels whose polar conditions are positive, and this component reduces the resolution of the image. Here, the reason why a positive color difference signal lowers the resolution will be explained in more detail.

As is well known, the screen brightness L is expressed by the following equation. L
−0.3Rγ+0.59Gγ+0.11Bγ [However,
R, G, and B are primary color signals, and γ is the gamma of the cathode ray tube, which usually takes a value of 2 to 3.

] The primary color signals R, G, and B are as shown in the following equation. R-EY+E
RY G-EY+EG-Y B-EY+EB-Y Therefore, L-0.3(EY+ER-Y)γ +0.59(EY+EG-Y)γ +0.11(EY+EB-Y)γ In the above formula, EY is a wideband signal, ER-Y, EG-Y, EB
-Y is a narrowband signal.

Since γ has a value of 2 to 3, most of the screen brightness L is composed of the one having a positive polarity among ER-Y, EG-Y, and EB-Y. For example, EY-1, ER-0.5, E
When O-E is 0.5, EB-Y- is 0.5, and γ-2, L-0,3 (0.25) + 0.59 (2,25) + 0.
11 (0.25), and among screen brightness, EG-Y
will account for a very large proportion. Therefore, the correct amount of correction cannot be obtained unless the amount of correction is determined by the positive color difference signal. Therefore, if the correction signal is added to the positive color difference signal, this correction signal itself becomes the chromatic luminance component on the screen. As a result, the resolution of the image is significantly improved.

If the color difference signals are directly supplied to the variable gain amplifier 15 as gain control signals without using the nonlinear transmission circuit 13, the correction signals added to the plurality of color difference signals will each generate a luminance component on the screen, They end up canceling each other out, making most images significantly less effective. Therefore, the nonlinear transmission circuit 13 has an essential and important meaning in the present invention. FIG. 7 is a block diagram showing another embodiment of the present invention.

Blocks with the same reference numerals as in FIGS. 2 and 3 represent the same components. In FIG. 7, the high frequency extraction circuit 14 includes a high frequency filter 22, a signal suppressor 26, and a brightness level detector 2.
7. Consists of a differentiation circuit 28 and an amplitude detector 29. The brightness level detector 27 is supplied with a brightness signal from the brightness signal source 12, and when the brightness signal level is above a specific level, it generates a detection signal and outputs a detection signal to the signal suppressor 2.
Supply to 6. When the detection signal is supplied, the signal suppressor 26 suppresses the high frequency component of the luminance signal supplied from the high-pass filter 22 so that the high frequency component is not transmitted to the variable gain amplifier 15. With this configuration, no correction signal is generated in image parts with high brightness.

In particular, if this configuration is applied to red color difference signals, it is possible to avoid correction for skin color, which is an image with relatively high brightness. The viewer's eyes are sensitive to skin tones, and even slight coloration or unnaturalness caused by the correction signal becomes a major drawback, so the above configuration provides favorable results. On the other hand, the luminance signal from the luminance signal source 12 is also supplied to a differentiation circuit 28, where a change in the luminance signal is detected.

This change is supplied to an amplitude detector 29. The amplitude detector 29 generates a detection signal when the amplitude of the change is large and supplies it to the signal suppressor. Therefore, when a change in the luminance signal is too large and an excessively large correction signal is generated, the signal suppressor 26 suppresses the high frequency component using the detection signal to prevent the high frequency component from being transmitted to the variable gain amplifier 15.

Such a configuration also suppresses the generation of undesirable correction signals and more effectively implements the present invention. Note that the high frequency extraction circuit 14 shown in FIGS. 3 and 7 is merely an example. , any device that is configured to substantially extract high frequency components of a luminance signal can be applied to the present invention.

As described above in detail, the present invention has a simple circuit configuration,
It is effective in significantly improving the resolution of color television images.

In particular, in the present invention, if the non-linear transmission circuit is configured to include a color difference signal limiter that suppresses color difference signals of a certain level or higher, it is effective in preventing generation of an unnecessarily large correction signal. . Furthermore, when the non-linear transmission circuit is configured to transmit only color difference signals of a positive specific level or higher, malfunctions can be prevented in monochrome images without color difference signals. Furthermore, if the non-linear transmission circuit is configured to remove and transmit color difference signals below a specific negative level, it will be effective in preventing generation of erroneous correction signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a block diagram showing a more detailed embodiment of the present invention, and FIGS. 4A, B, C, D, E,
F is a diagram showing a special case example of the non-linear transmission circuit used in the present invention, Fig. 5 A, B, CD and Fig. 6 A, b, c, d, e.
, f are signal waveform diagrams showing an example of signal processing according to the present invention, and FIG. 7 is a block diagram showing another embodiment of the present invention. 11... Color difference signal source, 12... Luminance signal source, 13... Non-linear transmission circuit, 14...
...High frequency extraction circuit, 15...Variable gain amplifier, 16...Addition device, 17,18...
Bias source, 20, 21... Diode, 19
...Resistor, 22...High-pass filter,
23... Base clip circuit, 24...
・Limiter 25...Color difference signal limiter, 26
... Signal suppressor, 27 ... Brightness level detector, 28 ... Differentiation circuit, 29 ...
Amplitude detector.

Claims (1)

[Claims] 1. A nonlinear transmission circuit that is connected to a color difference signal source and obtains a gain control signal by providing nonlinear transmission characteristics such as transmitting substantially only positive signals with respect to the level of the color difference signal. , a high frequency extraction circuit connected to the luminance signal source and extracting and outputting a high frequency component of the luminance signal, and each output of the nonlinear transmission circuit and the high frequency extraction circuit being supplied,
and a variable gain amplifier that obtains a correction signal by controlling a gain for a high frequency component of the luminance signal using the gain control signal so that the gain for the high frequency component increases when the level of the gain control signal is high; 1. An image quality improvement device for a color television receiver, comprising an amplifier, and an adding device that substantially adds the respective outputs of the color difference signal source and the luminance signal source to provide video display. 2. The image quality improvement device for a color television receiver according to claim 1, wherein the non-linear transmission circuit includes a color difference signal limiter that suppresses color difference signals of a specific level or higher. 3. The image quality improvement device for a color television receiver according to claim 1, wherein the non-linear transmission circuit is configured to transmit only color difference signals of a positive specific level or higher. 4. The image quality improvement device for a color television receiver according to claim 1, wherein the non-linear transmission circuit is configured to remove and transmit color difference signals below a specific negative level.