JPH0646445A - Picture quality improving circuit - Google Patents

Abstract

PURPOSE:To more emphasize the high band component of the luminance signal in a pattern of a green color or a cyan-color in comparison with other colors by providing a means which amplifiers the G-Y color difference signal to a chroma saturation detecting circuit which produces a control signal in accor dance with the chroma saturation. CONSTITUTION:When the color difference signals inputted to the input terminal 15a, 16a and 17a are shown with the output signals of a video camera referred to as R, G and B, the functions of R-Y=0.70R-0.59G-0.11B, B-Y=-0.30 R-0.59G+0.89B, and G-Y=0.30R+0.41G-0.11B are defined respectively. When a color difference signal of a 75% color bar is inputted to a chroma saturation detecting circuit 3a, the color difference signals R-Y and B-Y are inputted to a maximum value circuit with the ratio between both signals kept at a fixed level. However the color difference signal G-Y is inputted to a linear amplifier 23 and multiplied by alpha compared with the signals R-Y and B-Y. Thus alpha-multiple signal is outputted from the circuit 3a. In other words, a control signal emphasizes the luminance signal high band component of a pattern of a yellow color or a cyan-color in comparison with other colors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality improving circuit for improving the image quality by correcting the high frequency characteristic of a luminance signal which is deteriorated when transmitting a chromatic image signal.

[0002]

2. Description of the Related Art In the current color television systems such as NTSC, PAL, and SECAM systems, gamma correction and band limitation of color difference signals are performed on the transmitting side, so that detailed information of reproduced images in the receiver is in principle available. Has decreased. This means that as the color saturation (saturation) becomes higher (the color becomes darker), the amount of decrease in the luminance detail information becomes larger.

FIG. 5 is a graph in which the resolution deterioration of the NTSC signal is calculated and plotted. The vertical axis shows the deterioration degree of the resolution of the luminance signal, and the horizontal axis shows the color saturation (saturation degree).
In the figure, y, c, g, m, r, and b are yellow, cyan, and
It means green, magenta, red, and blue. That is, the high-frequency component of the luminance signal has the property of being deteriorated as the color saturation is higher, and the property of different deterioration depending on the color. Japanese Examined Patent Publication (Kokoku) No. 62-26234 proposes a circuit for ameliorating defects having different degrees of deterioration depending on colors. The point is to control the amount of high frequency components of the luminance signal by a control signal according to the saturation of the subject. To improve the image quality. Figure 6
Shows an example of the circuit.

In FIG. 6, 1 is an input terminal for a composite video signal of a luminance signal and a carrier color signal, 2 is an amplifier circuit for amplifying the carrier color signal, 3 is a saturation detection circuit, and 4 is transmission of a color signal and a luminance signal. Delay circuit for matching the time, 5 is a high pass filter, 6 is a low pass filter, 7 is a variable gain circuit,
8 is a gain control terminal, 9 is a color demodulation circuit, 10 is a luminance signal output terminal, 11, 12, 13 are (RY), (GY),
(BY) color difference signal output terminals, 14 is an adder circuit, 1
5, 16 and 17 are color difference signal input terminals, and 18 is a saturation signal output terminal.

The luminance signal that has passed through the delay circuit 4 is separated into a high-pass component and a low-pass component by a high-pass filter 5 and a low-pass filter 6, and the low-pass component is directly input to the adder circuit 14. On the other hand, the high frequency component is input to the variable gain circuit 7, and after gain control by the gain control voltage input to the terminal 8, that is, the control signal corresponding to the saturation of the image detected from the color difference signal by the saturation detection circuit 3. , And is applied to the adder circuit 14 to add the low-frequency component.

In a general image receiving device, detailed information on the luminance is lost and reproduced according to the saturation of the picture as described above. However, in the image receiving device incorporating the image quality improving means as shown in FIG. A gain control signal corresponding to the saturation is generated, and the gain variable circuit 7
Since the gain of the luminance signal increases, the amount of the high frequency component of the luminance signal added to the low frequency component of the luminance signal in the adding circuit 14 increases. That is, the higher the saturation of the image, the greater the amount of emphasis of the high frequency component of the luminance signal, and the deterioration of the detailed luminance information is corrected. For example, the amount of information that represents each red rose increases, and the outline of the image becomes clear.

The saturation detection circuit has a circuit configuration as shown in FIG. 19, 20, 21 are diodes, 22
Is the load resistance. Now, consider the case where the color difference signal FIGS. 8A to 8C corresponding to the 75% color bar is input to the color difference signal input terminal. 8A to 8C show (R-
Y), (BY), and (GY) color difference signal waveforms are shown, and the vertical axis in each figure is the relative value of the level with 100% white being 1. As can be seen, for example, in the case of red (RY), the color difference signal is at the highest voltage level and (G
Since the voltage levels of the color difference signals of -Y) and (BY) are lower than that, only the diode 19 conducts, and the diode 2
0 and 21 are non-conducting, and output terminal 18 is (RY)
A signal having the same voltage level as the color difference signal is obtained. (In the above, the forward offset voltage of the diode is ignored for the sake of easy understanding of the description.) Further, in the case of yellow, for example, the color difference signals of (RY) and (GY) are at the highest voltage level. , (BY), the voltage level of the color difference signal is lower than that, so that the diodes 19 and 20 are conducting, the diode 21 is non-conducting, and the output terminal 18 is (G-Y).
And signals of the same voltage level as the color difference signals of (RY) are obtained.

Similarly, in any other color, a signal having a voltage level equal to the color difference signal having a high voltage level can be obtained at the output terminal 18, so that a signal waveform as shown in FIG. Get as output signal.

Since the amplitude of the color difference signal changes in accordance with the color density, the magnitude of the signal obtained at the saturation signal output terminal 18 naturally changes accordingly. Then, as described above, the gain of the gain variable circuit 7 increases in accordance with this signal, so that the enhancement amount of the high frequency component of the luminance signal of the dark-colored picture portion becomes large and the deterioration of the luminance detail information is corrected. The image becomes clearer.

Further, comparing the chroma signal waveform of FIG. 8 (d) with the diagram showing the degree of deterioration of the high frequency component of the luminance shown in FIG. 5, these two figures have a complementary relationship. You can see that In other words, the voltage of the saturation signal is high for dark (low brightness level) colors such as red and blue, which have large deterioration of brightness detail information. Therefore, since the emphasis amount of the high frequency component of the luminance signal is increased according to the saturation signal voltage obtained in this way, the appropriate detail information of the luminance corresponding to the degree of deterioration of the luminance signal high frequency component of each color is obtained. Perform deterioration correction. The above-mentioned image quality improving circuit is designed for the purpose of correcting the deterioration amount of the luminance signal high frequency component in each color. Therefore, as a means for generating a control signal according to the color saturation, first, the carrier color signal is demodulated, and the color difference signal (R-
Y), (B-Y), (G-Y) are obtained, and then the maximum value of the color difference signals is obtained. Such a control signal generation circuit has a simple circuit configuration and can perform correction proportional to the deterioration amount of the luminance signal high frequency component. That is, in terms of colors, yellow, cyan, green, magenta,
The emphasis amount of the luminance signal high frequency component is increased in the order of red and blue. However, on the other hand, human beings have an impression or a sense of sharpness about colors, and it is not possible to make corrections that include them.

Generally, the color that does not give the human eyes a feeling of fatigue is green, which is a fresh color to the eye. Even in the images that appear on normal screens, there are many seasonal vegetables, fresh green plants, and vast lawns. Also, as a refreshing color,
There are also clear skies and wide seas. However, in this case, it can be said that the sky and sea are not dark blue, but rather a color close to cyan. All of them are colors that give the human eyes a freshness and comfort, and it is desirable to emphasize green and cyan in addition to the correction circuit as described above.

[0012]

In the above-mentioned conventional image quality improving circuit, although the amount of enhancement of the luminance signal high frequency component can be increased in the order of yellow, cyan, green, magenta, red and blue, However, there was an impression and a sharpness to the color, and it was not possible to correct a specific color including it.

According to the present invention, the deterioration of the high frequency component of the luminance signal according to the saturation is corrected, and the sharpness of the pattern in the green and cyan portions is improved, so that an image quality improving effect which is easy for human eyes can be obtained. An object of the present invention is to provide an image quality improving circuit capable of achieving the above.

[0014]

A saturation detection circuit for generating a control signal corresponding to the saturation of a chromatic color image is provided with a means for amplifying a G-Y color difference signal, so that it is green compared to other colors. The amount of enhancement of the high frequency component of the luminance signal in the pattern of the cyan part or the cyan part is increased.

[0015]

In order to detect the saturation, the carrier color signal is demodulated to produce a G-Y color difference signal, and the G-Y signal is amplified. Then, the color difference signals of BY, RY, and amplified G-Y are input to the maximum value circuit, and a control signal is obtained from the output terminal of the maximum value circuit. With this control signal, the amount of high frequency component of luminance of the picture portion is emphasized according to the saturation, and the deterioration of the luminance information of the details of the chromatic color image is corrected, and the correction or the emphasis of the deterioration degree of green and cyan is performed. .

[0016]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, which differs only in the configuration of the saturation detection circuit 3 of FIG.
The parts corresponding to are denoted by the same reference numerals, and the different parts will be mainly described here.

In FIG. 1, 15a, 16a and 17a are color difference signal input terminals of (RY), (BY) and (GY), 18a is a control signal output terminal and 23 is a gain α. A linear amplifier, 24 is a maximum value circuit.

In the following description, for the sake of simplicity, the gamma correction of the video camera will be set to 1. First, assuming that the output signals of the video camera are R, G, B, the input terminal 15
The color difference signals input to a, 16a, and 17a have the following relationship.

RY = 0.70R-0.59G-0.11B BY- = 0.30R-0.59G + 0.89B G-Y = -0.30R + 0.41G-0.11B 75% Color bar color difference signal When input to the degree detection circuit 3a, two signals (RY) and (BY) of the above three color difference signals are input to the maximum value circuit with the ratio kept constant, but (GY). Input to the linear amplifier 23,
Since it is multiplied by α, it becomes a signal that is α times greater than (RY) and (BY) and is output from the saturation detection circuit 3a.

The output signal waveform is as shown in FIG. 2, and the amplitude levels of yellow y, cyan c, and green g are multiplied by α. That is, by passing (G-Y) through the α-fold linear amplifier 23, the control signal becomes a control signal for emphasizing the luminance signal high frequency components of the patterns of yellow, cyan, and green as compared with other colors. This embodiment has an advantage that the yellow, cyan, and green patterns are sharper than the conventional one.

Next, another embodiment of the present invention will be described. In this embodiment, the linear amplifier 23 is replaced with a non-linear amplifier, and the other configurations are the same as those in FIG.

FIG. 3 shows an example of the characteristics of the non-linear amplifier. The horizontal axis is the saturation of green in the (G-Y) color difference signal, which means the saturation of green of the color bar,
The vertical axis represents the gain. In this example, the (G-Y) signal having 0 to 10% green saturation is tripled, 10 to 20% green saturation is doubled, and 20% or more green saturation is 1 time. The gain is set so that

Saturation 10% and 30% for clarity
FIG. 4 shows the input waveform and the output waveform when the (G-Y) color difference signal corresponding to the color bar of FIG. FIG. 4A shows an input signal to the nonlinear amplifier, which is a waveform on the positive side of the (G-Y) signal at a saturation of 10%. Since the amplitude levels of yellow y, cyan c, and green g do not exceed 10% of green g, the output signal is simply multiplied by 3 and the output signal shown in FIG.
The waveform is as shown in (b). On the other hand, when the (G-Y) signal at the saturation of 30% as shown in FIG. 4C is input, the waveform becomes as shown in FIG. 4D. This is because yellow y has a saturation of 10% or less of green g and is tripled, while cyan c has a saturation of 20% or more and 30% or less of green g, which is doubled, and green g is output as it is. .

By inserting an amplifier having such a non-linear characteristic in the (G-Y) signal path, it is possible to construct an image quality improving circuit capable of emphasizing the high frequency component of the luminance signal especially at low saturation.

In FIG. 3, which is shown as an example of the non-linear amplifier, the change point of the gain is 20% in the saturation of green. The reason for this is that greens with a saturation of more than 30% are rare in ordinary images, and even with highly saturated fresh greens and grasses, it is at most about 25%.

[0026]

As described above, the image quality improving circuit of the present invention not only improves the image quality by correcting the detailed information of the luminance in the dark pattern portion of the image but also improves the image quality of human beings such as green, cyan and yellow. It is possible to improve the visual impression and sharpness, and to exert a more human-friendly image quality improving effect.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention.

FIG. 2 is an output waveform diagram of FIG.

FIG. 3 is a characteristic diagram of an example of a non-linear amplifier used in another embodiment of the present invention.

FIG. 4A to FIG. 4D are input / output waveform diagrams in another embodiment of the present invention.

FIG. 5 is a characteristic diagram showing deterioration of a luminance signal with respect to saturation in a conventional NTSC television system.

FIG. 6 is a conventional circuit configuration diagram.

7 is a specific circuit diagram of the main part of FIG.

8A to 8D are input / output waveform diagrams in FIG.

[Explanation of symbols]

 3a ...... Saturation detection circuit 5 ...... High pass filter 6 ...... Low pass filter 7 ...... Variable gain circuit 9 ...... Color demodulation circuit 14 ...... Adder

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[Procedure amendment]

[Submission date] August 11, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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Claims (2)

[Claims] 1. A saturation detection circuit for generating a control signal based on the saturation of a chromatic image, a means for controlling the amount of a high frequency component of a luminance signal by the control signal, and as the saturation increases, It is characterized by comprising means for increasing the amount of high frequency components of the luminance signal, and means for generating a control signal in which the saturation of green is emphasized by the saturation detection circuit, and for making the design of the green part clearer. Image quality improvement circuit. 2. A saturation detection circuit for generating a control signal based on the saturation of a chromatic color image, means for controlling the amount of high frequency components of a luminance signal by the control signal, and as the saturation increases. An image quality improving circuit, characterized in that it comprises means for increasing the amount of high frequency components of a luminance signal, and the saturation detection circuit includes an amplifier for amplifying G-Y of a color difference signal.