JPH07298288A - Luminance color difference signal demodulation circuit and luminance color difference signal ratio correction circuit - Google Patents

Abstract

PURPOSE:To provide a luminance color difference signal demodulation circuit in which natural color reproduction is implemented even when a luminance signal is corrected with respect to frequency characteristics. CONSTITUTION:A Y/C separator circuit 1 separates a Y signal and a C signal from a video signal. The Y signal is given to a Y correction circuit 2, in which gamma correction is applied to be a signal Y' and a contour correction circuit 4 applies contour correction to the signal Y' to be a signal Y''. The C signal is given to a color demodulation circuit 5, in which the signal is demodulated to be color difference signals R-Y, B-Y. A luminance color difference signal ratio correction circuit 6 receives the signals Y, Y'' and the color difference signals R-Y, B-Y to modulate the color difference signals R-Y, B-Y depending on the correction of the frequency characteristic attended with the contour correction of the Y' signal to provide an output of color difference signals (R-Y)', (B-Y)'. Thus, a luminance color difference signal ratio is corrected and natural color reproduction is implemented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance / color difference signal demodulation circuit and a luminance / color difference signal ratio correction circuit which can perform natural color reproduction even if a luminance signal is subjected to correction of frequency characteristics such as contour correction.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional luminance / color difference signal demodulation circuit. In FIG. 4, a video signal is input to the Y / C separation circuit 1, and the Y / C separation circuit 1 outputs Y.
The (luminance) signal and the C (color) signal are separated and output. Y
The signal is input to a Y correction circuit 2 that performs gamma correction and is output as a Y ′ signal that has been gamma corrected. This Y '
The signal and the C signal output from the Y / C separation circuit 1 are input to a luminance / color signal ratio correction circuit 3 that corrects so as to keep the ratio of the luminance signal and the color signal constant.

The luminance / color signal ratio correction circuit 3 outputs the Y signal output from the Y / C separation circuit 1 which is a luminance signal before gamma correction.
The signal and the Y'signal output from the Y correction circuit 2 which is the luminance signal after gamma correction are input, and the modulation circuit 3 that modulates the C signal according to the output of the comparison circuit 3a.
It is roughly composed of b. For the detailed circuit of the luminance / color signal ratio correction circuit 3, for example, the configuration described in Japanese Patent Laid-Open No. 5-268622 can be used. Here, when the Y signal is subjected to static correction such as gamma correction as shown in FIG. 5A, the modulation circuit 3b in the luminance / color signal ratio correction circuit 3 makes the ratio between the luminance signal and the color signal constant. As shown in FIG. 5B, the C signal is corrected according to the output of the comparison circuit 3a and output as the C'signal.

Furthermore, Y'output from the Y correction circuit 2
The signal is input to the contour correction circuit 4 and is output as a Y ″ signal whose frequency characteristic has been corrected and contour correction has been performed. On the other hand, the C ′ signal output from the luminance / color signal ratio correction circuit 3 is a color demodulation circuit. The color demodulation circuit 5 is composed of a bandpass filter (BPF) 5a and a demodulator 5b for color demodulation, and demodulates the C'signal to obtain color difference signals RY and BY.
Is output.

[0005]

However, considering the frequency characteristics of the Y ″ signal output from the contour correction circuit 4 and the color difference signals RY and BY output from the color demodulation circuit 5, the contour correction circuit is considered. As described above, No. 4 corrects the frequency characteristic of the Y'signal as described above, the frequency characteristic of the Y "signal is the contour correction component as shown by the broken line in FIG. 6A in accordance with the input image quality adjustment signal. While BP is added
The frequency characteristics of the color difference signals RY and BY that are band-passed by the F5a for the 3.58 MHz component and demodulated by the demodulator 5b are as shown by the solid line in FIG. For the frequency characteristics of BY, BPF5a
Since it is outside the band of, the contour correction component as shown by the broken line cannot be added. For this reason, the ratio between the Y ″ signal and the color difference signals R-Y and B-Y output from the conventional luminance color difference signal demodulation circuit shown in FIG. 4 is not constant, and color reproduction becomes unnatural. There were dots.

This problem will be further described. Figure 7
As shown in (A), consider a pattern in which a region of brightness level 100 exists in the center of brightness level 75 with a single color of red. In this case, the luminance signal (Y signal) and the color difference signal R-
Y and BY have waveforms as shown in FIGS. 8A, 8B, and 8C, respectively. When contour correction is performed by the contour correction circuit 4 in FIG. 4, the luminance signal (Y ″ signal) has a waveform shown in FIG. 8D and the color difference signals RY,
BY is output in the waveform as it is in FIGS. 8B and 8C.

Then, in the R, G, B primary color signals restored by adding the luminance signal and the color difference signals output from the conventional luminance color difference signal demodulation circuit shown in FIG. 4, the R signal is as shown in FIG. Since the signal and the signal in FIG. 8D are added, the waveform becomes as shown in FIG. 8E, and the B signal is as shown in FIG.
Since the signal of (C) and the signal of FIG. 8 (D) are added, the waveform becomes as shown in FIG. 8 (F). Therefore,
The original red image shown in (A) produces white and black patterns in the portion where the brightness changes due to the contour correction, and as shown in FIG. White and black patterns occur at both ends, resulting in unnatural color reproduction.

According to such a principle, when contour correction is performed on a signal of all-green color, such as a leaf of a tree, white dots that should be all-green color should appear, or a red star in the night sky should glow white. There was a problem that natural color reproduction was achieved. The present invention has been made in view of the above problems, and provides a luminance color difference signal demodulation circuit and a luminance color difference signal ratio correction circuit that can perform natural color reproduction even if the luminance signal is corrected regarding frequency characteristics. The purpose is to provide.

[0009]

In order to solve the above-mentioned problems of the prior art, the present invention provides (1) a Y / C separation circuit which separates and outputs a luminance signal and a chrominance signal from an input video signal. A contour correction circuit that performs contour correction on the luminance signal output from the Y / C separation circuit and outputs the luminance signal;
A luminance / color difference signal demodulation circuit configured to demodulate the color signal output from the C separation circuit to output a color difference signal, in a luminance / color difference signal demodulation circuit output from the contour correction circuit. A luminance color-difference signal that is input with the luminance signal before contour correction by the contour correction circuit and the color difference signal output from the color demodulation circuit, and corrects and outputs the color difference signal according to the contour correction by the contour correction circuit. Provided is a luminance / color difference signal demodulation circuit having a luminance / color difference signal ratio correction circuit for correcting a ratio, and (2) a first luminance signal and correction relating to frequency characteristic before correction relating to frequency characteristic is provided. The second luminance signal subjected to the above is input, the comparison circuit for comparing the first and second luminance signals, and the first color difference signal are input, and the first color difference signal is input, and the first color difference signal is input according to the output of the comparison circuit. The color of A first modulation circuit that modulates and outputs the signal; and a second modulation circuit that receives the second color difference signal and that modulates and outputs the second color difference signal according to the output of the comparison circuit. It is intended to provide a luminance / color difference signal ratio correction circuit characterized by being provided and configured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A luminance color difference signal demodulation circuit and a luminance color difference signal ratio correction circuit according to the present invention will be described below with reference to the accompanying drawings. 1 is a block diagram showing an embodiment of a luminance color difference signal demodulation circuit and a luminance color difference signal ratio correction circuit of the present invention, FIG.
3 is a diagram for explaining the operation of the luminance / color difference signal demodulation circuit and the luminance / color difference signal ratio correction circuit of the present invention, and FIG. 3 is a diagram for explaining the operation of the luminance / color difference signal demodulation circuit and the luminance / color difference signal ratio correction circuit of the present invention. It is a waveform diagram. In FIG. 1, the same parts as those in FIG. 4 are designated by the same reference numerals.

In FIG. 1, a video signal is input to the Y / C separation circuit 1, and the Y / C separation circuit 1 separates and outputs a luminance (Y) signal and a color (C) signal. The Y signal is input to a Y correction circuit 2 that performs gamma correction and is output as a Y ′ signal that has been gamma corrected. The Y ′ signal output from the Y correction circuit 2 is input to the contour correction circuit 4 and is output as a Y ″ signal whose frequency characteristics have been corrected and contour correction has been performed. On the other hand, the Y / C separation circuit 1 outputs The generated C signal is input to the color demodulation circuit 5 including the BPF 5a and the demodulator 5b, the C signal is demodulated, and the color difference signal RY,
BY is output.

Further, in the luminance / color difference signal demodulation circuit of the present invention, the Y signal output from the Y / C separation circuit 1, the Y ″ signal output from the contour correction circuit 4, and the color demodulation circuit 5 are output. The luminance-color difference signal ratio correction circuit 6 corrects the color-difference signals R-Y and B-Y so that the ratio between the output luminance signal (Y ″ signal) and the color-difference signals R-Y and BY is constant.
Entered in.

The luminance / color difference signal ratio correction circuit 6 has a Y signal output from the Y / C separation circuit 1 which is a luminance signal before the contour correction circuit 4 corrects the frequency characteristic, and the contour correction circuit 4. To the output of the comparison circuit 6a, the comparison circuit 6a to which the Y ″ signal corrected for the frequency characteristic is input, the modulation circuit 6b that modulates the color difference signal RY according to the output of the comparison circuit 6a, and the output of the comparison circuit 6a. Accordingly, the configuration is substantially the same as that of the modulation circuit 6c that modulates the color difference signal B-Y.
When the luminance signal (Y ′ signal) is subjected to the contour correction by the contour correction circuit 4 as shown in FIG. 6A, the modulation circuits 6b and 6c in the luminance / color difference signal ratio correction circuit 6 change the luminance signal (Y ″). Signal) and the color difference signals R-Y and B-Y are kept constant, in accordance with the output of the comparison circuit 6a, as shown by the broken line in FIG. 6B, the color difference signals R-Y and B-Y. The corrected signals are output as color difference signals (RY) 'and (BY)'.

The operation of the luminance / color difference signal demodulating circuit of the present invention configured as above will be further described. Figure 2
As shown in (A), consider a pattern in which a region of brightness level 100 exists in the center of brightness level 75 with a single color of red. In this case, the luminance signal (Y signal) and the color difference signal R-
Y and BY have waveforms as shown in FIGS. 3A, 3B, and 3C, respectively. When contour correction is performed by the contour correction circuit 4 in FIG. 1, the luminance signal (Y ″ signal) has the waveform shown in FIG. 3D and the color difference signal R
-Y and BY are also corrected by the luminance / color difference signal ratio correction circuit 6 as described above, and the color difference signals (RY) 'and (BY)' shown in FIGS. 3 (E) and 3 (F) are obtained. Becomes the waveform of.

Then, in the R, G, B primary color signals restored by adding the luminance signal and the color difference signals output from the luminance color difference signal demodulation circuit of the present invention shown in FIG. 1, the R signal is shown in FIG. 3G and the signal in FIG. 3E are added, the waveform becomes as shown in FIG. 3G, and the B signal in FIG.
Since the signal of (D) and the signal of FIG. 8 (F) are added, the waveform becomes as shown in FIG. 3 (H). Therefore,
As shown in FIG. 2 (B), the image of the solid red color shown in FIG. 2 (A) changes in brightness level in order from the outside of both ends of the area of brightness level 100 as shown in FIG. 2 (B). Is less than 75 and dark red and brightness level is 10
A bright red pattern larger than 0 is generated, the contour is emphasized as it is, and the color is reproduced naturally.

Therefore, according to the luminance / color difference signal demodulating circuit of the present invention, the white and black patterns as described with reference to FIG. In this way, when contour correction is performed on the signal of all green, the problem that unnatural color reproduction such as white spots that should be all green should appear and red stars in the night sky glow white should be well resolved. Can be resolved.

[0017]

As described in detail above, the luminance / color difference signal demodulation circuit of the present invention receives the luminance signal after contour correction, the luminance signal before contour correction, and the color difference signal, and performs contour correction of the luminance signal. A luminance-color-difference signal-ratio correction circuit that corrects the luminance-color-difference signal ratio by correcting the color-difference signal according to the correction of the accompanying frequency characteristics is provided. The signal ratio can be made constant, and thus natural color reproduction can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the present invention.

FIG. 4 is a block diagram showing a conventional example.

5 is a characteristic diagram for explaining the operation of the Y correction circuit 2 in FIGS. 1 and 4. FIG.

FIG. 6 is a frequency characteristic diagram for explaining the problems of the conventional example.

FIG. 7 is a diagram for explaining the problems of the conventional example.

FIG. 8 is a waveform diagram for explaining the problems of the conventional example.

[Explanation of symbols]

 1 Y / C separation circuit 2 Y correction circuit 4 contour correction circuit 5 color demodulation circuit 5a band pass filter 5b demodulator 6 luminance color difference signal ratio correction circuit 6a comparison circuit 6b, 6c modulation circuit

Claims (2)

[Claims] 1. A Y / C separation circuit that separates and outputs a luminance signal and a color signal from an input video signal, and a contour that performs contour correction on the luminance signal output from the Y / C separation circuit and outputs the contour signal. A luminance / color difference signal demodulation circuit configured to include a correction circuit and a color demodulation circuit that demodulates the color signal output from the Y / C separation circuit and outputs a color difference signal. A luminance signal after contour correction, a luminance signal before contour correction by the contour correction circuit, and a color difference signal output from the color demodulation circuit are input, and the color difference signal is corrected according to the contour correction by the contour correction circuit. A luminance / color-difference signal demodulation circuit is provided with a luminance / color-difference signal ratio correction circuit that corrects the luminance / color-difference signal ratio that is output. 2. A first luminance signal before correction on frequency characteristics and a second brightness signal on which frequency characteristics are corrected.
Of the first luminance signal and the comparison circuit for comparing the first and second luminance signals, and the first color difference signal are input, and the first color difference signal is modulated according to the output of the comparison circuit. And a second modulation circuit that receives the second color difference signal and that modulates and outputs the second color difference signal according to the output of the comparison circuit. A luminance / color difference signal ratio correction circuit characterized by the above.