JPS6115633B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for improving the image quality of a color television receiver, and more particularly to an apparatus for correcting brightness errors thereof.

In current color television receivers, the xy chromaticity values of the three primary color phosphors (red, green, blue) are different from the xy chromaticity values of the NTSC phosphors. In addition, the color temperature of the white color reproduced on a color television receiver is also
Compared to the white color of the C light source determined by the NTSC system, the color has shifted to a bluish white color. Therefore, in color television receivers, in order to faithfully reproduce the colors sent from broadcasting stations, it is necessary to design the demodulation axis and demodulation gain of the color subcarrier to values different from the NTSC standard. . In particular, in the case of current color television receivers, it is necessary to prevent deterioration in skin color reproduction due to the fact that the xy chromaticity values of the green phosphor are different from those of the NTSC phosphor by increasing the red demodulation gain. Although this increase in red demodulation gain improves skin tone reproduction,
A large brightness error occurs for red colors, especially reds with high color saturation. For example, when an image of a red rose flower is reproduced on this color TV receiver, the color saturation of the flower becomes too high and the petals are distorted. The drawback is that the detailed images representing each image become invisible. Although red has been described as an example, changing the demodulation axis or demodulation gain of the color subcarrier similarly causes image details to be destroyed for other colors with high color saturation.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to ensure that even the details of images with high color saturation can be seen even in color television receivers in which the demodulation axis and demodulation gain of color subcarriers have been changed from the NTSC standard. The goal is to provide color images that can be reproduced.

A feature of the present invention is that when a highly saturated color is received, the high-frequency components of the image luminance signal are emphasized to prevent the details of the image from being destroyed.

An embodiment of the present invention is shown in FIG. In the figure, 1 is a color oversaturation detection circuit, 2 is a delay circuit, 3 is a high-pass filter, 4 is a switch changeover circuit, and 5 is an addition circuit. The color signal C (for example, red) is sent to the color oversaturation detection circuit 1.
pass through. At this time, when the color signal C has such a high degree of color saturation that it destroys the details of the picture on the screen of the color television receiver, a switch connection signal is sent from the color oversaturation detection circuit 1 to the switch changeover circuit 4. On the other hand, the luminance signal Y is divided into two parts and supplied to a delay circuit 2 and a high-pass filter 3, respectively. Delay circuit 2
is inserted in order to make the high-frequency component of the luminance signal passed through the high-pass filter 3 and the luminance signal passed through the delay circuit 2 coincide in time in the adder circuit 5.

Assuming that a color signal C with high color saturation is now input, the switch switching circuit 4 is closed by the output of the detection circuit 1, and the high frequency component of the luminance signal Y that has passed through the high frequency filter 3 is sent to the addition circuit 5. Because it is supplied,
As a result, the brightness signal has an increased high-frequency component, and detailed information in the image is reproduced more clearly.
Furthermore, in the case of a signal with low color saturation, the switch switching circuit 4 remains open, and a luminance signal with a natural gradation is output as in the conventional case.

FIG. 2 shows a second embodiment of the invention. 1~ in the diagram
5 has the same function as in Figure 1. 6 in the figure is a slice circuit that passes only the undershoot in the black direction among the high frequency components of the luminance signal Y. That is,
We focused on the fact that the distortion of screen details caused by changing the demodulation axis and demodulation gain of the color subcarrier mainly occurs when the luminance error increases in the positive direction.
In the method shown in FIG. 1 of the present invention, the second embodiment of the present invention is to add only the high-frequency components of the luminance signal toward black to sharpen the details of the screen.

According to the present invention, even in a color television receiver in which the demodulation axis or demodulation gain of the color subcarrier is changed, it is possible to correct the collapse of screen details due to a large brightness error, and it is possible to correct the collapse of screen details due to large brightness errors. Detailed images can be obtained even in red areas.

[Brief explanation of the drawing]

1 and 2 are block diagrams of embodiments of the present invention, respectively. 1...Color oversaturation detection circuit, 2...Delay circuit, 3
...High-pass filter, 4...Switch switching circuit, 5
...Addition circuit, 6...Slice circuit.

Claims (1)

[Scope of Claims] 1. Means for separating the high frequency component from the luminance signal, means for adding the high frequency component to the luminance signal, and means for detecting that the saturation of the color signal has become excessive. 1. A brightness error correction device for a color television receiver, characterized in that the high-frequency component is added to the brightness signal only during a period when the saturation of the color signal becomes excessive. 2 Among the high frequency components of the separated luminance signal,
The color device according to claim 1, further comprising a means for passing only a signal in the direction of the black level, and adding the signal in the direction of the black level to the luminance signal only during a period when the saturation of the color signal becomes excessive. Brightness error correction device for television receivers.