JPH0638074A - Picture quality adjusting circuit - Google Patents

Abstract

PURPOSE:To enable picture quality adjustment capable of keeping gradations over all the areas from a black level to a white level by adjusting contrast and luminance by detecting the peak of the white level and black level at a video signal part. CONSTITUTION:A blanking circuit 4 lowers a synchronizing signal level in the blanking block of a video signal down to a pedestal level and outputs the signal as a video signal, and the output of the circuit 4 is inputted to a white peak detection circuit 8 and a black peak detection circuit 6. When the white level is out of a reference, a white level error detection circuit 9 outputs an error signal, and a contrast adjusting circuit 2 is adjusted. When the black level is out of a reference, a black level error detection circuit 7 outputs an error signal, and a luminance adjusting circuit 3 is adjusted. Thus, the contrast and the luminance can be adjusted while keeping the gradation over all the areas from the black level to the white level without painting out a video signal input (a) in black or white.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality adjusting circuit for video equipment such as a television.

[0002]

2. Description of the Related Art FIG. 5 is an electric circuit block diagram of an image quality adjusting circuit showing a conventional example. As shown in FIG. 5, a video signal input is branched and one of them is contrast adjusting circuit 30 and brightness adjusting circuit 31. And outputs the video signal to the black peak detection circuit 32, the black peak detection circuit 32 detects the black level of the video signal input, and inputs the detection signal to the black level comparison circuit 33. The black level comparison circuit 33 compares it with the reference black level signal and inputs the comparison signal to the control terminal of the switch 34. Reference numeral 35 denotes an anode current detection circuit, which detects the beam current flowing in the CRT, converts it into a DC voltage and inputs it to the switch 34, and when the black level of the video signal input is lower than the reference black level signal. Switches the switch 34 to input the DC voltage to the contrast adjusting circuit 30 so that the contrast is weakened. When the black level of the video signal input is higher than the reference black level signal, the switch 34 is switched. The DC voltage is input to the brightness adjusting circuit 31 to lower the brightness. However, when the brightness level of the whole image is low, there is a problem that the gradation of the dark part is not used and black is crushed. When the brightness level of the entire image is high, the gradation of the bright part is not used and white is crushed. However, the image quality adjusting circuit has not been able to maintain the gradation over the entire range from the black level to the white level of the video signal.

[0003]

SUMMARY OF THE INVENTION According to the present invention, gradation is maintained over the entire area from a black level to a white level without causing black crushing or white crushing for a video signal input. It is an object of the present invention to provide an image quality adjustment circuit capable of adjusting contrast and brightness.

[0004]

FIG. 1 is an electric circuit block diagram of an image quality adjusting circuit showing an embodiment of the present invention.
As shown in the figure, in a picture quality adjusting circuit in which a contrast adjusting circuit 2 and a brightness adjusting circuit 3 adjust the contrast and brightness of a video signal input and outputs it as a video signal, a blanking circuit 4 is provided in an output circuit of the video signal. The same blanking circuit 4 lowers the sync signal level in the blanking interval of the video signal to the pedestal level and outputs it as a video signal. At the same time, the output is branched and one of them is input to the white peak detection circuit 8. , The other is the black peak detection circuit 6
, The white peak detection circuit 8 detects the white peak for each field and inputs it to the white level error detection circuit 9. If the white level error detection circuit 9 is out of the reference, it is compared with the white reference level. Error signal is output, the contrast adjustment circuit 2 is adjusted based on the error signal, the black peak detection circuit 6 detects a black peak for each field, and the detected black peak is input to the black level error detection circuit 7. If the input is out of the reference in 7, the error signal is output by comparing with the black reference level,
The brightness adjustment circuit 3 is adjusted based on the same error signal to perform image quality adjustment.

[0005]

According to the present invention, with the above-mentioned configuration, the contrast and the brightness are adjusted for the video signal input and then output. FIG. 4 is a waveform diagram of a video signal for explaining the operation of the image quality adjusting circuit of the present invention. In the figure, y indicates a white reference level and x indicates a black reference level. As shown in (A), when the video signal portion of the video signal input is between y and x, the video signal input is output as it is,
As shown in FIG. 6B, when the white level of the video signal portion of the video signal input exceeds y, the white level error detection circuit 9 detects the magnitude of the white level exceeding y and outputs the error signal. Is output and the gain of the amplifier used in the contrast adjustment circuit 2 is reduced based on the output so that the white level of the video signal falls within the range of y as shown in FIG. B) As shown in the figure, when the black level of the video signal portion of the video signal input is lower than x, the black level error detection circuit 9 detects the magnitude of the black level lower than x and detects the error. A signal is output, and based on the output, negative feedback is applied to the amplifier used in the brightness adjustment circuit 3 so that the black level of the video signal falls within the range of x as shown in FIG. Black level or black level without causing black level or black level. As gradation is maintained with respect to the entire area up to the white level from, it is possible to adjust the contrast and brightness.

[0006]

FIG. 1 is an electric circuit block diagram of an image quality adjusting circuit showing an embodiment of the present invention. Reference numeral 2 denotes a contrast adjustment circuit, which adjusts the contrast of the video signal input through the input terminal 1 and inputs it to the brightness adjustment circuit 3, and adjusts the brightness of the video signal input by the brightness adjustment circuit 3 to adjust the brightness. The signal is input to the ranking circuit 4, and the blanking circuit 4 lowers the level of the synchronizing signal and the like in the blanking section to the pedestal level so that the signal processing circuit thereafter does not erroneously detect a portion other than the video signal. Is output via the output terminal 5, and the same output is input to a video output circuit or the like for image display. The video signal output is branched so that one is input to the white peak detection circuit 8 and the other is input to the black peak detection circuit 6, and the white peak detection circuit 8 is input.
In order to detect the white peak of the video signal for each field, the detection signal is input to the white level error detection circuit 9, and when the input is out of the reference by the white level error detection circuit 9, The error signal is output in comparison with the white reference level and input to the adder 11, which is added to the current adjustment signal of the contrast adjustment circuit 2 and output to be input to the contrast adjustment circuit 2 for contrast adjustment. The gain of the amplifier used in the circuit 2 is adjusted. Therefore, as shown in FIG. 4 (B), when the white level of the video signal input exceeds the white reference level y, the gain of the amplifier used in the contrast adjustment circuit 2 is reduced to (C). As shown in the figure, the white level of the video signal can be set to the y level.

Similarly, the black peak detection circuit 6 is reset for each field so that the black peak of the video signal for each field can be detected, and the detection signal is input to the black level error detection circuit 7 to detect the black level error. When the input is out of the reference in the circuit 7, the error signal is compared with the black reference level and is output to the adder 10, which is then added to the current adjustment signal of the brightness adjustment circuit 3 and output. It is inputted to the brightness adjusting circuit 3 and negative feedback is applied to the amplifier used in the brightness adjusting circuit 3. Therefore, as shown in FIG. 4B, when the black level of the video signal input is lower than the black reference level x, negative feedback is applied to the amplifier used in the brightness adjustment circuit 3 to C) As shown in the figure, the black level of the video signal can be set to the level of x.

FIG. 2 is an explanatory view of the white level error detection circuit of FIG. 1, and FIG. 2A is an electric circuit block diagram,
FIG. 6B is a characteristic diagram of the limiter circuit. The white peak detection signal of the video signal for each field detected by the white peak detection circuit 8 is input to the limiter circuit 15, and in the limiter circuit 15, as shown in FIG. Output a constant reference level y, and outputs a level (a level exceeding the reference level y) corresponding to the input signal for an input (amount outside the reference) that exceeds a predetermined level. In this way, it is input to the sample hold circuit 16. In the sample hold circuit 16, the limiter circuit 1
5 holds and outputs the peak level of the input signal, and inputs the same to the comparison circuit 17, and the comparison circuit 17 compares the peak level input from the sample hold circuit 16 with a predetermined white reference level signal y to generate an error signal. And output terminal 18
Is input to the adder 11 of FIG.

FIG. 3 is an explanatory diagram of the black level error detection circuit of FIG. 1, and FIG. 3A is a block diagram of an electric circuit,
FIG. 6B is a characteristic diagram of the limiter circuit. The black peak detection signal of the video signal for each field detected by the black peak detection circuit 6 is input to the limiter circuit 20. In the limiter circuit 20, as shown in FIG. For example, a level (a level equal to or smaller than the reference level x) corresponding to the input signal is output, and a constant reference level x is output for an input exceeding a predetermined level. , To the sample and hold circuit 21. In the sample hold circuit 21, the limiter circuit 2
The peak level of the input signal from 0 is held and output, and is input to the comparison circuit 22. The comparison circuit 22 compares the peak level input from the sample hold circuit 21 with a predetermined black reference level signal x and outputs an error signal. And output terminal 23
It is input to the adder 10 of FIG.

In the comparison circuit 17 of FIG. 2, the comparison circuit 17 compares the peak level input from the sample and hold circuit 16 with a predetermined white reference level signal y, outputs a comparison signal, and outputs the same comparison signal. Based on this, the gain of the amplifier used in the contrast adjusting circuit 2 is adjusted, and when the peak level is lower than the predetermined white reference level signal y, the gain of the amplifier is increased so that the contrast becomes stronger.
When the peak level is higher than the predetermined white reference level signal y, the image quality may be adjusted by lowering the gain of the amplifier to weaken the contrast. If you do this,
If the contrast of the video signal input is too strong, compress it to make it weaker.If the contrast is too weak, extend the contrast to make it stronger, and the image quality should be sharp and easy to see. You can

[0011]

As described above, according to the present invention,
It is possible to adjust the contrast and brightness so that the gradation is maintained over the entire area from the black level to the white level without causing black crushing or white crushing for the video signal input. An image quality adjustment circuit can be provided, which greatly contributes to improving the performance of video equipment.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of an image quality adjustment circuit showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a white level error detection circuit of FIG.
The (A) diagram shows an electric circuit block diagram, and the (B) diagram shows
The characteristic diagram of a limiter circuit is shown.

3 is an explanatory diagram of the black level error detection circuit of FIG.
The (A) diagram shows an electric circuit block diagram, and the (B) diagram shows
The characteristic diagram of a limiter circuit is shown.

4A, 4B and 4C are waveform diagrams of a video signal for explaining the operation of the image quality adjusting circuit of the present invention.

FIG. 5 is a block diagram of an electric circuit of an image quality adjustment circuit showing a conventional example.

[Explanation of symbols]

 1 Input Terminal 2 Contrast Adjustment Circuit 3 Luminance Adjustment Circuit 4 Blanking Circuit 5 Output Terminal 6 Black Peak Detection Circuit 7 Black Level Error Detection Circuit 8 White Peak Detection Circuit 9 White Level Error Detection Circuit 10 Adder 11 Adder 15 Limiter Circuit 16 Sample hold circuit 17 Comparison circuit 18 Output terminal 20 Limiter circuit 21 Sample hold circuit 22 Comparison circuit 23 Output terminal 30 Contrast adjustment circuit 31 Brightness adjustment circuit 32 Black peak detection circuit 33 Black level comparison circuit 34 Switcher 35 Anode current detection circuit 36 Control circuit

Claims (2)

[Claims] 1. An image quality adjusting circuit, wherein a contrast adjusting circuit and a brightness adjusting circuit adjust a contrast and brightness of a video signal input and outputs the resulting image signal as a video signal. The ranking circuit lowers the sync signal level in the blanking interval of the video signal to the pedestal level and outputs it as a video signal.The output is branched and one is input to the white peak detection circuit and the other is input to the black peak detection circuit. , The white peak detection circuit detects the white peak of each field and inputs it to the white level error detection circuit.If the white level error detection circuit does not enter the input, the error signal is compared with the white reference level. And the contrast adjustment circuit is adjusted based on the same error signal, and the black peak detection circuit detects the black peak for each field to determine the black level. Input to the error detection circuit, and if the black level error detection circuit input is out of the reference, it outputs an error signal by comparing with the black reference level, and adjusts the brightness adjustment circuit based on the error signal to adjust the image quality. An image quality adjustment circuit characterized by: 2. The white level error detection circuit and the black level error detection circuit each hold a limiter circuit that suppresses and outputs an input signal with a predetermined limiter characteristic, and holds a peak level of an input signal from the limiter circuit. 2. An image quality adjusting apparatus according to claim 1, further comprising: a sample and hold circuit for outputting an error signal and a comparing circuit for comparing an input from the sample and hold circuit with a reference signal of a predetermined level and outputting an error signal. circuit.