JPH01154694A - Compensating circuit for picture sending gamma correction of television signal - Google Patents

Abstract

PURPOSE:To attain image sending side gamma correction without lowering detail by adding a compensation signal obtained by increasing by prescribed times the high area component of the signal of which luminance signal is gamma-corrected to the low area component of a gamma corrected luminance signal. CONSTITUTION:A luminance signal obtained at a matrix circuit 1 is inputted into an LPF circuit 2 and a luminance low area component is formed. On the other hand, a linear luminance signal is formed by a reverse gamma circuit 3 and a Y-matrix circuit 4. The luminance signal is given to an adding circuit 8 as the compensation signal of a high area component through a gamma circuit 5, a multiplication circuit 6 and an HPF circuit 7. The adding circuit 8 adds the said output to the output of the LPF circuit 2 and forms the luminance signal with the compensation of the gamma correction. The coefficient of the multiplication circuit 6 is formed at a coefficient formation circuit 9 based on a primary colors signal for example.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compensation system for gamma correction on the transmission side of television signals, and particularly to a compensation circuit for gamma correction suitable for reproduction of details in high-chroma images.

[Conventional technology]

In current television signals, in order to correct the gamma characteristics of the receiver, red, green, and blue (hereinafter referred to as R and G) are gamma-corrected on the image sending side in advance.

A luminance signal and nine color difference signals are generated from the B signal. However, since the single color difference signal is limited to within 1.5 MHz due to band limitations, there is a problem that details are reduced in high-chroma images. As a compensation system for solving this problem, for example, the one described in Japanese Patent Laid-Open No. 57-99089 is known.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology uses a single primary color image, for example, only one R signal.
It is effective in such cases. While doing so.

For an image in which three primary color signals are mixed, the high-frequency components of the luminance signal may become smaller due to compensation depending on the case, and as a result, there is a problem in that details are reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compensation circuit for gamma correction on the image transmission side that does not reduce details for either a primary color image or an image containing a mixture of three primary color signals.

[Means for solving problems]

The above purpose is linear R, G without gamma correction.

Gamma correction is performed using the high-frequency component YγC11 of the gamma-corrected luminance signal created by the B signal as a compensation signal, which is multiplied by (k>1) according to the ratio of the 3g color signal or color difference signal. This is achieved by adding it to the low frequency component YL of the luminance signal created by the R2O and B signals.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This embodiment shows a case where the input signals are syK color signals Rγ, Gγ, and Bγ that have undergone gamma correction.

The matrix circuit 1 receives 1Ill1 by the aff color signal.
The color difference signals I and Q are generated by the calculations shown below.

Yz=0.3Rγ+0.59Gγ+0.11+1γI
=0.6Rγ-0,28(3γ-0,32BγQ =
0.21Rγ−0,52Gγ+0.31 The luminance signal yt obtained by the Bγ matrix circuit 1 is
Then, the luminance low frequency component YL is generated.

On the other hand, the inverse gamma circuit 3 generates a linear 3g color signal RL.
,,GL,,! 31. The Y matrix circuit 4 calculates 0.3RL+0.59OL, 10, LIBL to generate a linear luminance signal Y. Then, the Δ gamma circuit 5 generates a gamma-corrected luminance signal Yγ,
A multiplication circuit 6 multiplies the signal by a coefficient k, and an HPF circuit 7 extracts this high frequency component as a compensation signal YγOH'. Then, an adding circuit 8 adds the YL times the signals to generate a luminance signal Y that has been compensated for by gamma correction.

The coefficients of the multiplication circuit are generated by the generation circuit 9 based on, for example, Rγ, Gγ, and Bγ multiplied signals. One characteristic of this coefficient is shown in FIG. 2. In the figure, the horizontal axis shows Bγ/Rγ, and the vertical axis shows Gγ/Rγ, and it can be considered that the three primary color signals are normalized by Rγ.

Bγ/Rγ clause 1.0 in the same figure. The region near the Gγ/Rγ phrase 1.0 corresponds to a so-called achromatic image (Rγ4Bγ4Gγ), and since there is no reduction in detail due to gamma correction in this region, it is set to =1.

On the other hand, as the image moves out of this area, the saturation of the image becomes higher. Therefore, by increasing the value of k as the image becomes more saturated, a compensation signal YγOH' without a decrease in detail is generated.

FIG. 3 shows an example of the configuration of the coefficient generation circuit 9.

Rγ, Gγ, Bγ times signal, quantization circuit 10
Quantize into bit QR, QG, and QB signals. Based on these quantized signals, the setting circuit 11 determines the coefficient k according to the characteristics shown in FIG. In addition, these childization circuits 10. The setting port 111 is, for example, a ROM
This can be easily achieved by Note that in setting the coefficients, it is also possible to use the RLI Gbg B@ signal shown in FIG.

FIG. 4 shows another embodiment of the present invention. This embodiment differs in that color difference signals I and Q are used to generate coefficients.

One characteristic generated by this coefficient is shown in FIG. 5. The horizontal axis of the fi'iI diagram is the color difference signal I, and the vertical axis is Q.

The vicinity of zero for both Q corresponds to a so-called achromatic image, and the image in this region is set to =1 because there is no reduction in detail due to gamma correction. On the other hand, since the further out of this area corresponds to an image with higher chroma, the value of k is also increased to generate a compensation signal YγCH' without a decrease in detail.

Next, another embodiment of the present invention will be described with reference to FIGS. 6 and 7. In this embodiment, the input signal is a linear primary color signal R1.
,,OL,BL times signal case. Since the operation and the like are the same as in FIG. 1, the explanation will be omitted since it can be easily understood from the drawing.

Note that the gamma circuit and inverse gamma circuit in Figure 1 can be easily realized using a ROM or the like.

Also, although it is possible to set the coefficient for each pixel,
In order to remove the influence of noise and the like, it is conceivable to use, for example, spatial smoothing between a plurality of adjacent pixels.

Further, when setting the coefficients, it is also possible to use a 3H color signal or a low frequency component of a color difference signal.

〔Effect of the invention〕

According to the present invention, in general, it is possible to realize gamma correction compensation without deterioration of details even for images with arbitrary mixing ratios of three primary color signals, which is a great help in improving the quality and definition of television images. effective.

It is clear that the embodiments of the present invention can be applied to analog signal formats, digital signal formats, or a mixed format of both.

Further, the passband of the HP F circuit 7 is preferably equal to or higher than the passband of the color difference signal, but it does not need to be particularly limited. Also,
It is desirable that the characteristics of the LPF circuit 2 be those of the 1-HPF circuit 7.

In this embodiment, I and Q are used as color difference signals, but it is obvious that the present invention can also be applied to RY, BY signals, etc.

[Brief explanation of the drawing]

FIG. 1, FIG. 4, FIG. 6, and FIG. 7 are all block diagrams showing the configuration of a compensation circuit according to an embodiment of the present invention, and FIG. 2 and FIG. 5 are characteristic diagrams of compensation coefficients. FIG. 3 is a block diagram of a coefficient generation circuit. 1... Matrix circuit, 2... LPF circuit, 3.
... Inverse gamma circuit, 4... Y matrix circuit, 5...
・Gamma circuit, 6...Multiplication circuit, 7...HP k?
Circuit, 8...addition circuit, 9...coefficient generation circuit, 1
0...Quantization circuit, 11...k setting circuit.

Claims (1)

[Claims] 1. Means for generating high-frequency components of a luminance signal composed of linear red, green, and blue signals and subjected to gamma correction; and means for generating a low-frequency component of a luminance signal composed of gamma-corrected red, green, and blue signals, and adds a signal obtained by multiplying the high-frequency component by k to the low-frequency component signal. 1. A compensation circuit for gamma correction on an image transmission side of a television signal, the compensation circuit comprising a luminance signal corrected by the above.