JPH0451675A - Video signal correction circuit - Google Patents

Abstract

PURPOSE:To obtain a video signal which is suitable for an input signal and has few rough feelings and in addition, has sharpness by providing plural pieces of coring circuits different in their coring widths, and selecting the coring circuit with the coring width at which coring circuit output starts to change. CONSTITUTION:Plural pieces of the coring circuit 3, 4 are provided, and a switch circuit 6 which switches selectively the coring circuit 3, 4 with the coring width at which the coring circuit output starts to change and connects it to an addition circuit 7 is provided. Then, when the SN ratio of a video signal is good, the output of the coring circuit 3 with the smallest coring width is selected by the switch circuit 6, and is added to the video input signal by the addition circuit 7, and besides, when the SN ratio is bad, the output of the coring circuit 4 with the large coring width is selected by the switch circuit 6, and is added to the video input signal by the addition circuit 7. Thus, the coring circuits 3, 4 with the coring width most suitable for the video input signal are set, and a picture in which the sharpness and a noise feeling are balanced can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field: This invention relates to video signal correction circuits in color television receivers, monitor devices, and the like.

(b) Prior Art FIG. 3 is a block diagram showing a conventional video signal correction circuit.

The video signal from the video signal input terminal (1) is input to the adder circuit (7) and also to the contour compensation circuit (2).

If the video signal input has a waveform as shown in FIG. 2(A), the waveform output from the contour compensation circuit (2) will be as shown in FIG. 2(B). Then, by simply adding the output signal from the contour compensation circuit (2) and the video signal input in the adder circuit (7), a video signal with sharpness as shown in FIG. 2 (CC) can be obtained.

However, when a video signal with a poor S/N ratio is input as shown in Figure 2 (D), the output waveform from the contour compensation circuit (2) becomes as shown in Figure 2 (F), and the screen At the top, the image becomes grainy and unsightly.

In order to reduce this roughness, a coring circuit (15
), and the coring width is changed from Fig. 2 (E) to Fig. 2 (G).
) and set it to the desired value. However, if the coring width is large, the output waveform will change as shown in Figure 2 (I(
), the graininess on the screen will be reduced, but the sharpness will be dull and the image will look flat.

For example, conventionally, such technology was developed in U.S. Pat.
It is also shown in Publication No. 8 (HO4N 5/21).

(c) Problems to be Solved by the Invention As described above, conventional video signal correction circuits have had problems such as noticeable roughness and decreased sharpness depending on the selection of the coring width.

In order to solve the above problems, the present invention has a plurality of coring circuits with different coring widths, and by selecting a coring circuit with a coring width at which the coring circuit output starts to change, the input signal is It is possible to obtain a video signal correction circuit with less residual roughness and sharpness.

(d) Means for solving the problem The present invention has a plurality of coring circuits in order to determine whether the S/N of the video signal input is good or bad based on the output of the coring circuit, and the coring circuit output starts to change. This is a video signal correction circuit equipped with a switch circuit that selectively switches a coring circuit having a coring width and transmits the selected coring circuit to an adder circuit.

(e) When the S/N ratio of the input video signal is good, the output of the coring circuit with the smallest width of 77127 is output from the coring circuit by the switch circuit, added to the video input signal by the adder circuit, and , when the S/N ratio is poor, the output of the 27127 circuit with a large coring width is output from the coring circuit by the switch circuit, and added to the video input signal by the adding circuit.

(f) Embodiment An embodiment of this invention will be described with reference to the drawings. 1st
The figure is a block diagram showing an example of the video signal correction circuit of this invention.

The video signal from the video signal input terminal (1) is input to the adder circuit (A) and also to the contour complement 1 circuit (2).

First, when the video signal input has a waveform as shown in Figure 2 (A>), the output signal from the contour compensation circuit (2) is as shown in Figure 2 (A>).
The waveform will be as shown in B).

This signal is transmitted to the first coring circuit with a small coring width (
3) and a second core non-circuit with a large coring width (4
), the signals are cored with the core I song amplitudes as shown in FIG. 2 (1) and (J), respectively, and the cored signals are input to the level comparison circuit (5).

The signals input from the first coring circuit (3) and the second coring circuit (4) are each limited by a limiter circuit (11) to eliminate the difference in signal level due to the coring width, and then differentially amplified. A comparator circuit (14) compares the voltage that has been removed in phase by a circuit (12) and further averaged by a full-wave rectifier circuit (13) with a reference voltage vr.

Then, for a signal with a good S/N ratio as shown in Figure 2 (A),
In this case, the output signal from the first coring circuit (3) is output by the switch circuit (6) to the adder circuit (7).

Therefore, in the case of an input signal with a good S/N, the adder circuit (
The output signal of step 7) becomes as shown in FIG. 2(C), and since the coring width can be set small, the feeling of sluggishness can be suppressed.

Next, the video signal input is S/
In the case of a video signal with a poor N ratio, the output signal from the contour compensation circuit (2) has a waveform as shown in FIG. 2(F).

When this signal is input to the first core 1 nong circuit (3) with a small coring width and the 7i12 coa cung circuit (4) with a large coring width, the signals shown in Fig. 2 (K) and (
Coring is performed with a coring width such as L). Then, each cored signal is sent to a level comparison circuit (5
) is input.

First coring circuit (3), second coring circuit (4)
Each of the human-generated signals is sent to a limiter circuit (11).
After applying a limiter to eliminate the difference in signal level due to the coring width, the differential amplifier circuit (12) removes the common mode, and the full-wave rectifier circuit (13) averages the voltage and the reference voltage Vr. are compared by a comparison circuit (14).

In the case of a signal with poor S/'N as shown in Fig. 2 (D), the signal input to the limiter circuit (11) differs depending on the coring width, so differential amplification can extract the noise signal and completely eliminate the noise signal. When the wave is rectified and averaged, the reference voltage Vr
be higher than

In this case, the output signal of the second coring circuit (4) is output by the switch circuit (6) to the adder circuit (7). By doing so, when the S/N is poor, the output of the adder circuit (7) becomes as shown in FIG. 2 (H), and by setting a large coring width, noise can be reduced.

In the embodiment of the present invention, two coring circuits have been described, but it goes without saying that by increasing the number of coring circuits, a coring circuit with a more optimal coring width can be selected.

(g) Effects of the Invention As described above, according to the present invention, it is possible to set a coring circuit with an optimal coring width for video signal input, and it is possible to create pictures with a good balance between sharpness and noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the video signal correction circuit of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the video signal correction circuit of the present invention and the operation of a conventional example, and FIG. 1 is a block diagram showing a conventional video signal correction circuit. (2)...Contour compensation circuit, (3)...First coring circuit, (4)...Second coring circuit, (5)...
... Level comparison circuit, (6) ... Switch circuit, (7
)...addition circuit.

Claims (1)

[Claims] (1) A contour compensation circuit connected to a video signal input terminal, a plurality of coring circuits connected after the contour compensation circuit, a circuit for comparing the output levels of the plurality of coring circuits, and this comparison circuit. 1. A video signal correction circuit comprising: a switch circuit that selectively switches and transmits one of a plurality of coring circuits; and a circuit that adds an output of the switch circuit and a video signal input terminal signal.