JPS5928317B2 - Color stabilization device for color television receivers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color stabilizing device for a color television receiver that reproduces stable skin colors.

In the color reproduction of color television receivers, the most important thing is the reproduction characteristics of skin color, but this skin color is affected by various factors, such as changes in the lighting in the studio, the characteristics of the three primary color filters of the imaging camera, the characteristics of the transmission line, etc. The color is reproduced differently from the original color due to the differential phase, differential gain, etc. of the television receiver. In order to reduce the distortion of skin color caused by these factors, the following configuration has been adopted in the past.

To explain this with reference to FIG. 1, the reference color signal is a signal having a phase corresponding to the skin color and a constant amplitude, and this reference color signal is supplied to the amplitude modulator 1, and the luminance signal that is separately supplied is undergoes amplitude modulation. By this operation, the amplitude of the amplitude-modulated reference color signal output from the amplitude modulator 1 and the luminance signal level always maintain a constant ratio, so the amplitude-modulated reference color signal is The signal is indicative of skin color in any case. The subtracter 3 generates a difference signal between the carrier color signal input and the signal representing the skin color, and transmits it to the amplitude detector 4. The amplitude detector 4 detects the amplitude of the difference signal and transmits it to the variable gain amplifier 5 to control its gain. That is, the amplitude of the difference signal represents how much the color represented by the carrier color signal differs from the skin color, and the larger the amplitude of the difference signal, the larger the difference between the two colors. The variable gain amplifier 5 amplifies the difference signal, and its amplification factor is controlled by the amplitude of the difference signal. That is, the larger the amplitude of the difference signal, the lower the amplification factor, and the smaller the amplitude of the difference signal, the higher the amplitude factor.As a result, the obtained difference signal is supplied to the adder 6.

An adder 6 adds the carrier color signal and the difference signal.
With the above configuration, if the color represented by the carrier color signal is very different from the skin color, no signal is output from the variable gain amplifier 5, so the carrier color signal input to the adder 6 is output as is. be done.

On the other hand, when the color represented by the carrier color signal is close to skin tone, the difference signal between the reference color signal and the carrier color signal is supplied from the variable gain amplifier 5 to the adder 6, and when this is added to the carrier color signal, The carrier color signals contained in both signals cancel each other out, leaving only the reference color signal. That is, the carrier color signal input to the adder 6 is converted into a reference color signal and output.
As described above, the conventional color stabilizing device operates to draw the carrier color signal near the skin color into the skin color, but it has the following drawbacks.

The first is that it does not operate reliably when the luminance signal is small.

That is, when the luminance signal is small, the reference color signal output from the amplitude modulator 1 becomes small accordingly. This reduced reference color signal represents the skin color, but if it is extremely small, it becomes difficult to compare it with the carrier color signal, and amplitude detection, which represents the difference between the color represented by the carrier color signal and the skin color, becomes difficult. The output of the amplifier 4 becomes so small that the variable gain amplifier 5 cannot be controlled sufficiently. This will be explained in more detail.

For example, when the amplitude value of the reference color signal output from the amplitude modulator 1 in FIG. 2v (However, in this example, it is assumed that the gain of the subtracter 3 is 1 and there is no phase difference between the two input signals.) If a signal with the same color tone as this signal example and one-tenth the brightness is transmitted, the luminance signal will be one-tenth the brightness, and the carrier color signal will also be tenth the brightness in proportion to the luminance signal. It has become the number one. Therefore, the amplitude modulator 1 operates so that the reference color signal outputted from the amplitude modulator 1 is also reduced to one tenth. At this time, the amplitude values of the input signal to the subtracter 3 are 0.1V and 0.0V.
8V, and the output of the subtracter 3 becomes 0.02V. Naturally, therefore, the SN ratio deteriorates and the accuracy of comparison decreases, but the difference in color tone is the same in the above two cases, and it is originally desirable that the output level of the subtracter 3 be the same. Subtractor 3
When the output signal level of the signal decreases, the output of the amplitude detector 4 that detects the amplitude level decreases.

In other words, in an image with a low luminance signal level, in other words, in a dark image, even if the signal has a color tone that is quite different from the skin tone, it will only appear as a small signal in the output signal of the amplitude detector 4, so the color that is very similar to the skin tone will appear. This means that you are making an erroneous judgment.

For this reason, a red image, which is different from the skin color, is determined to be close to the skin color. Specifically, the variable gain amplifier 5 outputs a large amount of a skin color correction signal and supplies it to the adder 6, resulting in an undesirable operation in which a red image is converted to a skin color. Second
is the phase difference between the carrier color signals included in the two signals input to the adder 6.

The carrier color signal has a component that is supplied to the adder 6 via the subtracter 3 and the variable gain amplifier 5, and a component that is supplied directly to the adder 6, but both components are completely canceled in the adder 6. For this to happen, the polarities must be opposite and the amplitude and phase must match. However, the carrier color signal component passing through the subtracter 3 and the variable gain amplifier 5 often has a phase delay, and therefore tends to cause a phase difference with the carrier color signal component directly supplied to the adder 6. Therefore, the two components may not completely cancel each other out, and the skin tone may not be completely drawn in. The present invention detects a signal near the skin color based on the amplitude of the difference signal between the reference color signal of the skin color and the carrier color signal, and controls the mixing ratio of the carrier color signal and the reference color signal using the detection signal. The present invention provides a color stabilizing device that solves the problems of the conventional example described above.

The present invention will be explained below based on the embodiment shown in FIG.
In FIG. 2, a carrier chrominance signal is supplied to a variable gain amplifier 7, and its gain is controlled by a separately supplied luminance signal. Here, the control characteristics are set such that the gain increases as the luminance signal level decreases. The output of the variable gain amplifier 7 is supplied to one input terminal of the subtracter 3, where it is subtracted from the reference color signal supplied to the other input terminal. To explain the above operation, consider the case where the carrier color signal phase matches the reference color signal phase.

When the luminance signal is small, the amplitude of the corresponding skin color signal decreases. At this time, the gain of the variable gain amplifier 7 is increasing, so when the amplitude of the carrier color signal is relatively small, it matches the amplitude of the reference color signal at the input terminal of the subtracter 3. This means that signals with relatively small amplitudes are determined to represent skin color. Conversely, when the luminance signal is large, the gain of the variable gain amplifier 7 is reduced, so when the amplitude of the carrier color signal is relatively large, it matches the amplitude of the reference color signal and is determined to be skin color. That is, it is possible to always determine an appropriate carrier color signal amplitude as skin color depending on the luminance signal level. Moreover, unlike the conventional example described above, the reference color signal supplied to the subtracter 3 is at a constant level, so it is easy to compare it with the carrier color signal. The difference signal output from the subtracter 3 is supplied to an amplitude detector 4, where the amplitude of the difference signal is detected and sent to a variable mixer 8.
transmitted to. A carrier color signal is supplied to the variable mixer 8, and a reference color signal whose amplitude is modulated by a luminance signal in the amplitude modulator 1 is also supplied, and both signals are combined with a control signal representing the amplitude of the difference signal. They are mixed in an appropriate ratio and output. The amplitude modulator 1 has a characteristic opposite to that of the variable gain amplifier 7, and is set so that when the luminance signal level is small, the amplitude of the output reference color signal becomes small. With the above configuration, the carrier color signal is directly supplied to the variable mixer 8, while the reference color signal is supplied only through the amplitude modulator 1, so the difference in the amount of phase shift received by both signals is Since it is smaller than the conventional example described above, a highly accurate retracting operation can be performed.

As described above in detail, the present invention eliminates the drawbacks of conventional color toning devices and can perform stable and accurate control operations, and its effects are extremely significant.

Note that the present invention is not limited to the case where a reference color signal corresponding to skin color is provided, and it goes without saying that it can be effectively implemented to stabilize any other color.

[Brief explanation of the drawing]

FIG. 1 is a main part block diagram showing a conventional example, and FIG. 2 is a main part block diagram showing an embodiment of the present invention. 1...Amplitude modulator, 3...Subtractor, 4
. . . Amplitude detector, 7 . . . Variable gain amplifier, 8 . . . Variable mixer.

Claims (1)

[Scope of Claims] 1. A control circuit that controls the carrier color signal based on the amplitude of a difference signal between the carrier color signal and the reference color signal, and an amplitude modulator and a variable mixer provided in the color signal transmission system, The amplitude modulator is supplied with the reference color signal and the luminance signal, and is configured to amplitude-modulate the reference color signal depending on the luminance signal level, and the variable mixer is configured to supply the carrier color signal and the amplitude modulator. and a control signal representing the amplitude of the difference signal, and the mixing ratio of the carrier color signal and the output signal of the amplitude modulator is controlled by the control signal. A color stabilizing device for color television receivers. 2. In the description of claim 1, the control circuit includes a variable gain amplifier and a subtracter, and the variable gain amplifier is supplied with the carrier color signal and the luminance signal, and the carrier color increases as the luminance signal increases. The subtracter is configured to reduce the amplification factor for the signal, and the subtracter is configured to be supplied with the carrier color signal output from the variable gain amplifier and the reference color signal, and output a difference signal between the two. A color stabilizing device for a color television receiver, characterized in that the mixing ratio of the variable mixer is controlled by the amplitude of a signal.