JPH03188769A - Picture quality adjustment circuit - Google Patents

Abstract

PURPOSE:To attain contour emphasis processing in response to S/N of an input video signal by varying the degree of contour emphasis of the video signal in response to a difference between a white peak level and a black peak level of the input video signal. CONSTITUTION:An adder circuit 8 adds a level control signal D at a prescribed level outputted from a level control circuit 9 and an addition detection signal G and an addition signal obtained from the adder circuit 8 is fed to a contour extraction circuit 3 as a gain control signal D'. The gain control of the contour signal is implemented based on the gain control signal D' outputted from the gain control circuit comprising the adder circuit 8 and the level control circuit 9 by the circuit 3. Even when a video signal with low S/N and much noise is inputted, the contour emphasis processing is implemented to a degree not causing displeasure. Then when the video signal A with excellent S/N is inputted to the input terminal 1, the video signal C improving the sharpness of the picture more is extracted from an output terminal 4.

Description

[Detailed Description of the Invention] [Objective of the Invention j (Industrial Application Field) The present invention improves image quality by emphasizing the contours of video signals in television receivers, video tape recorders (VTRs), etc. This invention relates to an image quality adjustment circuit.

(Prior Art) Generally, a signal processing circuit such as a television receiver or a VTR is provided with an image quality adjustment circuit for performing edge enhancement processing to improve the clarity of an image. FIG. 4 shows a conventional example of such an image quality adjustment circuit.

In this figure, a video signal a input to an input terminal 11 is supplied to an outline extraction circuit 13 and one input terminal of an addition circuit 12. The contour extraction circuit 13 extracts the contour portion (edge portion) P (see FIG. 5) of the input video signal a, and the extracted contour signal is controlled to an appropriate level by the level control circuit 19. Later, adder circuit 1
2 is supplied to the other input terminal of 2. Here, the contour extraction circuit 13 is composed of a second-order differential circuit, a delay line, and the like.

In the adder circuit 12, the original video signal a and the contour signal S are added, and from the output terminal 14, a video signal C subjected to contour enhancement processing is taken out.

Figure 5 shows the signal waveforms of each part of this image quality adjustment circuit, where the waveform in (a) is the input video signal a, the waveform in <b> is the contour signal b, and the waveform in (c) is for the image quality adjustment. The subsequent output video signals C are shown respectively.

(Problem to be Solved by the Invention) By the way, the above-mentioned conventional image quality adjustment circuit that performs edge enhancement processing is a high frequency enhancement circuit, and even noise components are emphasized, so the SiN ratio of the output signal C is There was a problem in that the value decreased.

Therefore, the amount of contour enhancement should be limited in advance to a level that does not make the image unsightly even when a signal with a poor S/N ratio is input, or the level should be reduced each time such a signal is input. I had to. - Therefore, the amount of edge enhancement for a signal with a relatively good S/N ratio was not always set appropriately, and a clear image was not always obtained.

The present invention has been proposed in order to solve such problems, and an object of the present invention is to provide an image quality adjustment circuit that can perform optimal edge enhancement processing regardless of the degree of S/N ratio of an input video signal. With the goal.

"Structure of the Invention" (Means for Solving the Problems) In order to achieve the above object, an image quality adjustment circuit according to the present invention includes a contour extraction circuit that detects edge portions of an input video signal and extracts a contour signal; A level detection circuit that detects a white peak level and a black peak level of an input video signal and outputs a detection signal corresponding to the difference between these white peak level and black peak level, and the detection signal outputted from this level detection circuit. The present invention is characterized by comprising a gain control circuit that controls the gain of the contour signal based on the above, and an addition circuit that adds the gain-controlled contour signal to the input video signal.

(Function) According to the above-described configuration, since the gain of the contour signal is controlled based on the detection signal corresponding to the difference between the white peak level and the black peak level, the gain of the contour signal is controlled according to the S/N ratio of the input video signal. Contour enhancement processing can be performed.

Therefore, for a noisy input video signal, S
, /'N ratio is not deteriorated, and it is also possible to perform signal processing with a high degree of edge emphasis on an input video signal with a good S/'N ratio.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

The block diagram of FIG. 1 shows one embodiment of an image quality adjustment circuit according to the present invention.

In this figure, an input video signal A that enters an input terminal 1 is supplied to an adder circuit 2 and also to a contour extraction circuit 3, where a contour portion (edge portion) is extracted. In the adder circuit 2, the gain-controlled contour signal B output from the contour extraction circuit 3 is added to the input video signal, and a video signal C in which the contour portion is emphasized is taken out from the output terminal 4.

On the other hand, the input video signal is supplied to a white peak detection circuit 5 and a black peak detection circuit 6, and a white peak detection signal E and a black peak detection signal F detected by these detection circuits 5 and 6 are added to an adder circuit 7. After the addition, this addition detection signal G is supplied to the addition circuit 8. Note that the white peak detection circuit 5,
The black peak detection circuit F1116 and the addition circuit #I7 detect the detection signal G corresponding to the difference between the white peak level and the black peak level.
Configure a level detection circuit that outputs.

In the addition circuit 88, the level control signal of a predetermined level outputted from the level control circuit 9 and the addition detection signal G are added, and the addition signal obtained from the addition circuit 8 is used as a gain control signal to feed the contour extraction circuit 3. is supplied to In this contour extraction circuit 3, the addition circuit 8
Gain control of the contour signal is performed based on this gain control signal outputted from a gain control circuit consisting of a level control circuit 9 and a level control circuit 9.

In the image quality adjustment circuit configured as described above, a control signal of a predetermined level (for example, 3 dB up), which is normally set in advance by the level control circuit 9, is supplied to the contour extraction circuit 3, and the contour is determined by this level control signal. Since the signal level is adjusted, even if a noisy video signal with a low S/N ratio is input, contour enhancement processing can be performed to a degree that does not make the image unsightly.

Generally speaking, increasing the level of the 2 to 3 MHz frequency signal will have a great effect on edge enhancement, but if the increased level is kept within 3 dB, the S/R after edge enhancement processing will improve even for noisy video signals. The deterioration of the N ratio is not childish.

Next, a case will be described in which a video signal A with a good S/N ratio is input to the input terminal 1.

First, in detecting a white peak, the white peak detection circuit 5 clamps the leading end of the synchronizing signal sy of the video signal A to a constant voltage as shown in FIG.
% (shaded area) m is detected, and a DC voltage signal proportional to this white peak portion m is generated. This DC voltage signal corresponds to the white peak detection signal E.

In addition, when detecting a black peak, the black peak detection circuit 6 first converts the input video signal A shown in FIG. 3(a) into the input video signal A shown in FIG.
) and clamp the pedestal part as shown. Next, as shown in Fig. 3(C), after blanking the part of the synchronizing signal sy, the black peak part (shaded part) where the video signal level is lower than the 20% level is detected, and this black peak is detected. A DC voltage signal proportional to the peak portion n is obtained and output as a black peak detection signal F.

The obtained white peak detection signal E and black peak detection signal F are added by an adding circuit 7. At this time, when the average brightness of the video signal is higher, the S/N ratio is higher and noise is less noticeable. Therefore, when adding the two peak detection signals, if the white peak detection signal E is larger, the addition output will be larger. The white peak detection signal E is weighted and added so that The addition detection signal G obtained in this way corresponds to the difference between the white peak and the black peak, and the larger the addition detection signal G is, the higher the level from the white peak to the black peak of the video signal A is. This indicates that the S/N ratio of the signal is high, and the signal is sharp. For such a video signal A, it is expected that the sharpness of the image will be improved by increasing the amount of edge enhancement.

The addition detection signal G is added to a constant level control signal supplied from the level control circuit 9 in the addition circuit 8, and is supplied to the contour extraction circuit 3 as a gain control signal D', so that the S/N ratio is For video signal A with a high level of contrast, the level control circuit 9 can perform edge enhancement processing to a greater degree than the amount of edge enhancement preset, and output the video signal C with higher image clarity to the output terminal. It can be extracted from 4.

[Effects of the Invention] As explained above, according to the present invention, the degree of edge enhancement of the video signal can be changed according to the difference between the white peak level and the black peak level of the input video signal. The amount of edge enhancement can be suppressed for video signals with a large number of signals so as not to deteriorate the S/N ratio, and the amount of edge enhancement can be increased for video signals with a good S/N ratio to produce a clearer image. You can adjust the image quality to achieve the desired result.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the image quality adjustment circuit according to the present invention, FIG. 2 is a waveform diagram for explaining the operation of the white peak detection circuit that constitutes the image quality adjustment circuit of FIG. 1, and FIG. is a waveform diagram for explaining the operation of the black peak detection circuit that constitutes the image quality adjustment circuit in Figure 1, Figure 4 is a block diagram showing the conventional image quality adjustment circuit, and Figure 5 is the operation of the conventional image quality adjustment circuit. FIG. 2 is a waveform diagram for explaining. 2.7.8...Addition circuit 3...Contour extraction circuit 5...White peak detection circuit 6...Black peak detection circuit 9...Level control circuit m...White peak portion n...・Black peak part

Claims (1)

[Claims] A contour extraction circuit detects the edge portion of the input video signal and extracts a contour signal, and a contour extraction circuit detects the white peak level and black peak level of the input video signal and corresponds to the difference between the white peak level and the black peak level. a level detection circuit that outputs a detection signal; a gain control circuit that controls the gain of the contour signal based on the detection signal output from the level detection circuit; and a gain control circuit that applies the gain-controlled contour signal to the input video signal. An image quality adjustment circuit comprising an addition circuit that performs addition.