JP2003009172A - Image signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image signal processing circuit for correcting chroma effectively and improving picture quality. SOLUTION: A histogram creation circuit 12 detects the distribution of an amplitude value in each specific period of R, G, and B signals. Compression circuits 14-16 compress the R, G, and B signals. A gain control circuit 13 controls a compression gain in the compression circuits 14-16 according to the amplitude distribution of the R, G, and B signals. Adjustment circuits 17-19 adjust the amplitude value of the R, G, and B signals that have been compressed by the compression circuits 14-16.

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a video signal processing circuit used for an image display device such as a television receiver or a monitor device, and more particularly to a video signal processing circuit for effectively reducing saturation. And a video signal processing circuit capable of improving image quality. 2. Description of the Related Art In an image display device such as a television receiver or a monitor device, a gamma correction process is performed as a video signal process on a luminance signal to improve image quality by effectively using a dynamic range of the image display device. Let me. FIG. 3 is a block diagram showing an example of a conventional video signal processing circuit. In FIG. 3, a composite video signal input from an input terminal 1 is input to a Y / C separation circuit 2 and separated into a luminance signal Y and a carrier chrominance signal C. The color signal C is input to the color demodulation circuit 3 and demodulated into two color difference signals Cb and Cr. [0003] The luminance signal Y is input to a luminance signal processing circuit 4, subjected to signal processing for the luminance signal Y described later, and output from an output terminal 6 as a luminance signal Y '. The color difference signals Cb and Cr are input to the color signal processing circuit 5, where signal processing such as color adjustment and tint adjustment is performed on the color difference signals Cb and Cr, and output from the output terminals 7 and 8 as color difference signals Cb 'and Cr'. You. Here, an example of signal processing in the luminance signal processing circuit 4 will be described with reference to FIG. The signal processing by the luminance signal processing circuit 4 is gamma correction processing as an example. The gamma correction process is to adaptively control the input / output characteristics of the luminance signal Y in accordance with the video content in order to effectively use the limited dynamic range of the television transmission system. In FIG. 4, (A) shows a linear relationship between the input Y signal (the luminance signal Y input to the luminance signal processing circuit 4) and the output Y signal (the luminance signal Y 'output to the luminance signal processing circuit 4). Is shown. The gamma correction processing includes, for example, white-side gamma correction and black-side gamma correction. As shown in FIG. 4B, by giving the input / output characteristics on the white side non-linearity, white gradation can be suppressed and halation due to a white peak signal can be prevented. Also, as shown in FIG. 4C, by increasing the intermediate gradation so that the 100% white signal becomes equivalent to the linear input / output characteristic shown in FIG.
It is possible to increase the contrast of the intermediate gradation and reproduce a sharp image. Further, for an image in which black is floating, as shown in FIG. 4D, the black level of the image is lowered and the gradation on the black side is raised. As a result, the contrast in the dark part can be identified, and the black is drawn into the original black, so that a tighter image can be reproduced. In this way, the contrast of the luminance level portion to be enhanced is improved, and the image quality is improved. [0007] In the conventional video signal processing circuit described above, only processing for a luminance signal is performed, and similar processing is not performed for a chrominance signal.
There has been a problem that the color becomes light and whitish in a region where only the gradation of the luminance signal is increased by the gamma correction processing of the luminance signal, and the color becomes dark in a region where only the gradation of the luminance signal is reduced. That is, in the conventional video signal processing circuit, the color reproducibility tends to deteriorate, and there has been a problem that an image having an optimum saturation cannot be obtained. The present invention has been made in view of the above problems, and has as its object to provide a video signal processing circuit capable of effectively correcting saturation and improving image quality. . According to the present invention, in order to solve the above-mentioned problems of the prior art, a video signal processing circuit for processing a video signal is provided for each of three primary colors R, G and B signals. An amplitude distribution detecting means (12) for detecting a distribution of amplitude values in a period, a compression circuit (14 to 16) for compressing each of the R, G, and B signals; and an amplitude distribution detecting means for detecting the amplitude detected by the amplitude distribution detecting means. A gain control circuit (13) for controlling a compression gain in the compression circuit according to the distribution;
An adjustment circuit (17) for adjusting the amplitude value of each of the G and B signals
To 19) are provided. A video signal processing circuit according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention.
Is a diagram for explaining the operation of the video signal processing circuit of the present invention.
FIG. 4 is a diagram illustrating a histogram of a primary color signal. In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals. In FIG. 1, a composite video signal input from an input terminal 1 is input to a Y / C separation circuit 2 and separated into a luminance signal Y and a carrier chrominance signal C. The color signal C is input to the color demodulation circuit 3 and demodulated into two color difference signals Cb and Cr. The luminance signal Y and the color difference signals Cb, Cr are input to an RGB conversion circuit 11, and are output from three primary color signals R, G, B (hereinafter, referred to as R, G, B).
(R, G, B signals). The R, G, and B signals are input to a histogram creation circuit 12 and compression circuits 14 to 16. The histogram creation circuit 12 stores the values of the R, G, and B signals in a plurality of fields, and
As shown in (A), a histogram is created for each of the R, G, and B signals. Note that the horizontal axis in FIG. 2 is the amplitude value data, and the vertical axis is the frequency (integrated value). By creating a histogram of the R, G, B signals for a predetermined period, it is possible to detect how the R, G, B signals are distributed in a range from a minimum value 0 to a maximum value 255 (in the case of 8 bits). can do. By detecting the distribution of the video, it can be determined whether the input video signal is a dark video or a bright video as a whole. A detection signal indicating the distribution range detected by the histogram creation circuit 12 is input to a gain control circuit 13 and adjustment circuits 17 to 19. Gain control circuit 13
Controls the gain of compression in the compression circuits 14 to 16 according to the detection signal input from the histogram creation circuit 12. The compression circuits 14 to 16 set a position shifted from 0 by a predetermined level a as a minimum value of the distribution range as a new minimum value, and newly set a position shifted from 255 by a predetermined level a from 255 as a maximum value of the distribution range. The maximum value.
The R, G, and B signals are compressed in the direction of the median. By increasing the minimum value by level a and decreasing the maximum value by level a, the R ', G',
The histogram of the B 'signal is as shown in FIG. The level a in FIG. 2B corresponds to the detection signal input from the histogram creation circuit 12. That is, if the video signal is originally distributed over almost the entire range of 0 to 255, the level a is large, and the video signal is originally distributed only in the intermediate range of 0 to 255, for example. For example, the level a is set to small (including 0). By compressing the input R, G, and B signals so as to form a signal having a histogram as shown in FIG. 2B, the R, G, and B signals are respectively compressed and decompressed in the subsequent processing. Alternatively, arbitrary processing (adjustment) such as movement of the amplitude value can be performed. The compression circuits 14 to 1
6, the compression is performed in common for the R, G, and B signals, so that the balance of the R, G, and B signals is not lost. The above processing is represented by the following equation. Here, only the R signal is shown, but the same applies to the G and B signals. In the following equations (1) to (3), K is a compression ratio (gain). When R> 127, R ′ = {(R-127) × K} +127 (1) When R <127, R ′ = (R × K) + (a−1) (2) K = (128− a) / 128 (3) R ', output from the compression circuits 14 to 16
The G 'and B' signals are input to adjustment circuits 17 to 19.
The adjustment circuits 17 to 19 arbitrarily adjust the amplitude values of the R ', G', and B 'signals. Any one of R ', G', B 'signals
One or two signals may be adjusted, or all signals may be adjusted. The adjusting circuits 17 to 19 compress or expand the R ', G', B 'signals according to the characteristics of the display device. Alternatively, the adjustment circuits 17 to 19 shift the amplitude values of the R ', G', and B 'signals so as to brighten a dark image or conversely adjust a bright image to a dark image. To shift the amplitude value means to shift the distribution range in FIG. Such an arbitrary adjustment can be made by compressing the R, G, and B signals in advance by the compression circuits 14 to 16. R ″ output from the adjustment circuits 17 to 19,
The G "and B" signals are input to a Y / CbCr conversion circuit 20 and converted into a luminance signal Y "and color difference signals Cb" and Cr ". The luminance signal Y" is output from an output terminal 21 and a color difference signal Cb. ", Cr" are output from the output terminals 22 and 23. According to the present invention, not only the saturation is corrected, but also the contrast of the luminance signal Y ″ output from the Y / CbCr conversion circuit 20 is improved.
It is possible to obtain a high-quality image with a rich number of colors and a sense of depth and three-dimensionality. The luminance signal Y ″ may be further subjected to a conventional gamma correction process. As described above in detail, the video signal processing circuit according to the present invention employs three primary colors. Amplitude distribution detecting means for detecting the distribution of the amplitude value of each of the R, G, and B signals in a predetermined period; a compression circuit for compressing each of the R, G, and B signals;
A gain control circuit for controlling a compression gain of the compression circuit in accordance with the distribution of the amplitude detected by the amplitude distribution detection means, and an adjustment for adjusting the amplitude values of the R, G, and B signals compressed by the compression circuit. Since the circuit is provided with the circuit, the saturation can be effectively corrected, and the image quality can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing a histogram of three primary color signals for explaining the operation of the present invention. FIG. 3 is a block diagram showing a conventional example. FIG. 4 is a characteristic diagram for explaining the operation of the conventional example. [Description of Signs] 2 Y / C separation circuit 3 Color demodulation circuit 11 RGB conversion circuit 12 Histogram creation circuit 13 Gain control circuits 14 to 16 Compression circuits 17 to 19 Adjustment circuit 20 Y / CbCr conversion circuit

Continuation of front page    F term (reference) 5B057 CA01 CA08 CA12 CA16 CB01                       CB08 CB11 CE17 CH08                 5C066 CA05 EA05 EC05 GA01 GA33                       KA12 KD01 KD06 KD07 KE01                       KE09 KE24 KP02                 5C077 LL19 MP08 PP15 PP32 PP34                       PP37 PQ12 PQ19 SS06                 5C079 HB01 HB04 LB02 MA11 MA17                       NA03 PA05

Claims (1)

1. A video signal processing circuit for processing a video signal, comprising: amplitude distribution detecting means for detecting a distribution of amplitude values of respective three primary colors R, G, and B signals in a predetermined period; , G, and B signals, a gain control circuit that controls a compression gain in the compression circuit in accordance with the amplitude distribution detected by the amplitude distribution detection means, A video signal processing circuit comprising: an adjustment circuit for adjusting the amplitude values of the R, G, and B signals.