JP3192212B2 - Color television signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color television signal processing circuit for converting an R, G, B video signal into a luminance signal and a color difference signal for processing.

[0002]

2. Description of the Related Art The effect of the current television system performing gamma correction on the image transmitting side will be briefly described. In the current television system, after converting the three primary color signals E _R , E _G , E _B of _R , _G , _B into a luminance signal E _Y and color difference signals E _Q , E _I , the color difference signal is band-limited. It is superimposed on the luminance signal E _Y by modulating a chrominance subcarrier. These are expressed by the following equations: E _Y = 0.3E _R + 0.59E _G + 0.11E _B E _Q = 0.41 (E _B −E _Y ) +0.48 (E _R −E _Y ) E _I = −0 .27 (E _B -E _Y ) +0.74 (E _R -E _Y ). For example, when a color television signal E _M, the _{E M = E Y +0.493 (E} B -E Y) sinωt +0.877 (E R -E Y) cosωt.

[0003] Since the color difference signals are high-frequency component is limited, E _R, the high frequency component of E _G, each signal E _B is transmitted only with the luminance signal E _Y. For example, when a red pure color object is photographed on the image transmission side, the high-frequency and low-frequency components of the E _R signal are respectively represented by E _RH and E _RL.
And if the luminance signal is E _YH , E _YL , E _R = E
_RL + E _RH, because it is _{E G = E B = 0,} E R signal reproduced by the receiver side, the E _RL + E _YH. E _YH is E _G , E
It is also reproduced as a _B signal. By the way, originally gamma correction is C
Since it corrects the emission characteristics of the RT, the E _R signal reproduced by the receiver

[0004]

Equation 1 should be taken into account, and E _G ,
As E _B signals, it should be subjected to the same gamma correction in E _YH signal reproduced. However, in the current television system, E _R, E _G, at the stage of E _B signals

[0005]

The gamma correction is performed such that For this reason, considering the above-described case of a pure red object having a high degree of saturation, the E _R signal reproduced on the receiver side is E _R = E _RL + 0.3E _RH .

If a high-frequency component is superimposed on the E _R signal, the high-frequency signal is sent to a gamma correction circuit on the image transmission side to generate an E _{R signal.}
It is increased or decreased according to the level of the low frequency component of the signal, and in this case, it is usually raised to the power of 0.45. On the other hand, in the receiver, the high-frequency signal is raised to the power of 2.22 due to the light emission characteristics of the CRT, and the combined gain becomes one. On the other hand, this high-frequency signal is E _G ,
Although not be reproduced as E _B signal, in this case the original E _G, since E _B signal levels are both are 0, reproduction E _G, E _B signal and E _G = E _B = 0.3E _RH Become.

The _ERH is raised to the power of 0.45 by the gamma correction circuit as described above. CR for E _R signal
T is 2.22 square by the emission characteristics of, but gain the combined transmission and reception is not 1 lead times, does not emit light is on CRT Since E _G, the signal level in the case of E _B signal close to zero. That is, in this case high frequency components will not be reproduced as E _G, E _B signal, the high frequency signal is reproduced from only E _R signal, the level is reduced to the original 0.3 times.
Similarly, it occurs in a case with a high degree of saturation, such as a pure green or blue pure subject. That is, in the current television system, the resolution is degraded by a signal having a high color saturation.

As a conventional method for solving this problem, there is JP-A-63-67890. This configuration is shown in FIG. 5, and the method will be described below. The R, G, and B signals subjected to gamma correction by gamma correction circuits 4 to 6 are supplied to a matrix circuit 8, and the luminance signal Y 'is synthesized by this circuit. I do. The luminance signal Y 'each luminance signal Y _H through high pass filter 11 and low pass filter 12' to obtain the luminance signal Y _L '.
Further, the gamma correction circuit 9 performs gamma correction on the luminance signal obtained by the matrix circuit 7 for the R, G, and B signals before gamma correction, thereby obtaining a luminance signal Y _L that has passed through the low-pass filter 10. Then, the division circuit 15 calculates Y _L / Y _L ′, multiplies this output by the multiplication circuit 18 by the luminance signal Y _H ′, and adds the luminance signal Y _L ′ by the addition circuit 19. This is to obtain a corrected luminance signal.

When this method is used, the correction coefficient Y _L / Y _L ′ has a gain of 1 or more in a high-saturation image with high color saturation, so that the high-frequency component Y _H of the luminance signal is amplified and the current television is amplified. In this way, the resolution of high chroma images is improved.
The high-frequency component of a subject having a pure red color and a saturation of 100% is amplified by 1.9 times, and the subject of a pure blue color having a saturation of 100% is amplified by about 3.4 times. However, this method has the following problems. For example, when the input signal source is a camera, the S / N of the blue signal is poor. Therefore, when a large gain is applied, the S / N of the luminance signal output on the image transmission side for a blue subject becomes very poor.

[0010]

The above-mentioned prior art includes the following.
For example, for a blue signal such as a blue object with a saturation of 100%, the S / N is poor and the gain is increased by about 3.4 times, so that there is a drawback that the high frequency noise component sharply increases. . An object of the present invention is to realize a device in which the S / N of a signal for a blue object is improved by selectively suppressing a correction gain for a blue hue.

[0011]

According to the present invention, in order to achieve the above object, means for detecting color saturation and hue from R, G, B input signals, and gamma correction of the R, G, B signals, respectively. Means for mixing the luminance signal at a predetermined ratio and synthesizing the luminance signal; means for extracting the high-frequency component of the luminance signal; It is characterized in that means for controlling based on the output of the means is used.

[0012]

As a result, it is possible to selectively suppress the high-frequency correction gain for a specific color, for example, a blue hue, and to suppress the deterioration of the S / N due to the high-frequency correction of the high chroma image of the subject of the color.

[0013]

An embodiment of the present invention will be described with reference to FIG. After the R, G, and B signals 1 to 3 before gamma correction are gamma corrected by gamma correction circuits 4 to 6, respectively, a matrix circuit 8 obtains a luminance signal Y 'and color difference signals I', Q '. Here, the luminance signal Y 'is supplied to the high-pass filter 11 and the low-pass filter 12.
Separated by a cutoff frequency of the color difference signal 'and low-frequency component Y _L' high frequency components Y _H in the color difference signals I 'and Q' are band-limited by the cutoff frequency of the color difference signal by the low pass filters 13 and 14. Further, the gamma correction before the R, G, B signal 1-3 is supplied to a matrix circuit 7, wherein obtaining a luminance signal Y _S.
Then, to obtain a luminance signal Y and gamma corrected Y _S, to obtain a low-frequency component Y _L low pass filter 10. The R, G, and B signals before gamma correction are output to a hue dependent circuit 16.
And output as hue dependent gain G
obtain _a.

The low-frequency components Y of Y and Y 'thus determined
The ratio of Y _L / Y _L 'is calculated by the division circuit 15 for supplying _L and Y _L '. A multiplication circuit 17 that supplies this ratio and the hue dependent gain G _a calculates a correction gain of G _a · Y _L / Y _L '. The multiplication circuit 18 controls the gain of the luminance signal Y _H ′ using the output of the multiplication circuit 17. The output of the multiplication circuit 18 'are added in the addition circuit 19, color signals I and its output' luminance signal Y _L, sends to the encoder 20 together with Q ', obtain a composite color television signal.

Here, the hue dependent circuit will be described with reference to FIG. Hue indexing circuit 2 from original signals R, G, B
In step 1, the achromatic component is removed and separated into complementary and primary color components. The phase angle is derived from this output by the vector angle determination circuit 22 from the level amounts of the complementary color and the primary color by using the trigonometric function theorem. Then, by converting this angle into a desired gain characteristic by the conversion table 23, a hue dependent circuit can be realized.

With the above operation, the present invention adjusts the correction gain of the luminance signal Y _H ′ with the hue dependent gain for the blue hue as shown in FIG. 2 to suppress the deterioration of S / N. Thus, high-frequency components are corrected for the respective degrees of saturation of R, G, and B as shown in FIG. For example, in the case of the blue object described in the conventional example, the saturation degree of pure color is 100%.
% (B = 1, R = G = 0), assuming that a very high frequency component is present, the correction gain becomes 3.4 times. Therefore, in the conventional method, deterioration of S / N is a serious problem for a blue subject having a large amount of noise components. On the other hand, when the present invention is used, the correction gain is appropriately suppressed only in the case of a blue subject having many noise components, and the other conventional red and green subjects have the same conventional correction gain to appropriately correct the resolution deteriorated on the image receiving side. I do.

[0017]

As described above, when the present invention is used, the deterioration of the resolution of a high chroma image in the current television system is faithfully corrected, and the correction gain is lowered for a blue object having a poor S / N. , S / N and high image quality can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a correction gain characteristic of hue dependent.

FIG. 3 is a block diagram illustrating an embodiment of a hue dependent circuit.

FIG. 4 is a diagram showing a correction gain characteristic of the present invention.

FIG. 5 is a block diagram showing a conventional example.

[Explanation of symbols]

 1-3 R, G, B input terminals 4, 5, 6, 9 Gamma correction circuit 7, 8 Matrix circuit 11 Low pass filter 12, 13, 14 Low pass filter 15 Division circuit 16 Hue dependent circuit 17, 18 Multiplication circuit 19 Addition Circuit 20 Encoder 21 Hue Indexing Circuit 22 Vector Angle Indexing Circuit 23 Conversion Table

Claims (2)

(57) [Claims] 1. A means for detecting a color saturation and a hue from an R, G, B input signal, and a means for gamma-correcting the R, G, B signals and then mixing them at a predetermined ratio to synthesize a luminance signal. Means for extracting a high-frequency component of the luminance signal, and means for controlling an amplification factor for the high-frequency component of the extracted luminance signal by an output of the means for detecting the color saturation and the hue. Television signal processing circuit. Wherein R, G, and means for obtaining a first luminance signal Y _S B signals by matrix conversion, and means for obtaining a first luminance signal Y _S and gamma correction second luminance signal Y , Above R,
G, the separation B signals 'means for obtaining a third luminance signal Y' third luminance signal Y and the gamma correction signal to matrix conversion respectively high frequency components from the Y _H ', the low-frequency component Y _L' in extracting means, and means for obtaining a fourth luminance signal Y _L taken out only the low-frequency component of the second luminance signal Y, the R, G, and dependent gain to blue hue from B signals to means and, these fourth luminance signal Y _L and the low frequency component Y _L of the third luminance signal 'in ratio by considering the hue dependent gain of the high frequency component Y _H of the third luminance signal' Means for controlling the gain of the color television signal.