JPH0898189A - Video signal processing circuit - Google Patents

Abstract

PURPOSE: To attain the reduction of a false chrominance signal and obtain a wide band for a chrominance signal, and in addition, to effectively suppress the influence of a large amplitude edge by providing a filter whose passing band of a chrominance signal component changes in accordance with the output level of a circuit to detect the edge in the horizontal direction of a picture. CONSTITUTION: The output of an A/D conversion circuit 3 and a signal obtained by delaying this by one-line delay circuits 4 and 5 are inputted to an edge detection circuit 19. The edge detection circuit 19 detects the edge in the horizontal direction (vertical edge) of the picture, and outputs a control signal to a variable coefficient + fixed coefficient low pass filter 20. In the variable coefficient + fixed coefficient low pass filter 20, the coefficient of a variable coefficient low pass filter is changed by the control signal, and filtering whose characteristic is different for the edge part and the flat part of the picture is executed. By changing the coefficient of the filter by the signal of the detection of the edge in the horizontal direction of the picture, the chrominance false signal of the edge part can be suppressed perfectly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit used in a CCD single plate color video camera device or the like.

[0002]

2. Description of the Related Art FIG. 9 shows a block diagram of a video signal processing circuit in a conventional CCD single plate color video camera. Here, an example by digital signal processing is shown. CCD
Takes an example in which the complementary color checkered filter shown in FIG. 10 is used and CR lines and CB lines are read alternately from the CCD.

In FIG. 9, an output signal of the CCD image sensor 1 is subjected to correlated double sampling and gain adjustment in a CDS / AGC circuit, and then converted into a digital signal by an AD conversion circuit 3. Then, a luminance signal (Y signal) and a carrier color signal (C signal) are generated from the output of the AD conversion circuit 3.

The luminance signal first suppresses the chrominance signal component by passing the output of the 1-line delay circuit 4 through a low-pass filter 6. Next, the horizontal aperture compensation signal generated by the horizontal aperture compensation circuit 7 and the vertical aperture compensation signal generated by the vertical aperture compensation circuit 8 are mixed together by a mixing circuit 9
A luminance signal component in which the aperture is compensated is obtained by mixing in. Then, after the gamma correction circuit 10 performs gamma correction, the D / A conversion circuit 11 converts the gamma correction signal into an analog signal to obtain an analog luminance signal.

On the other hand, a color signal is made up of repeated information of two lines and two horizontal pixels. In FIG. 10, the horizontal repetition is (S1, S2, S1, S2, ...) And the vertical repetition is (CR, CB, CR, CB,
..), the output read as a mixture of upper and lower two pixels is CRS1 = Ye + Mg CRS2 = Cy + G CBS2 = Ye + G CBS2 = Cy + Mg.

These signals converted into digital signals by the A / D conversion circuit 3 have color false signals suppressed by the low-pass filter 12 and sent to the matrix circuit 13.
Here, the low-pass filter 12 averages the output signal of the A / D conversion circuit 3 and the output signal of the 1-line delay circuit 5. Then, the signal obtained by filtering the signal on the CR line and the signal obtained by filtering the signal on the CB line are output to the matrix circuit 13.

The matrix circuit 13 calculates CRS1 + CRS2 = CBS1 + CBS2 = Ye + Mg by adding / subtracting the output of the low-pass filter 12.
+ Cy + G = 2R + 3G + 2B≈Y CRS1−CRS2 = 2R−G≈R−Y CBS1−CBS2 = − (2B−G) ≈− (B−Y), so three components of R, G, and B are obtained from them. Separate each color signal.

White balance adjustment is performed in the white balance circuit 14 using the R, G, and B color signals,
The gamma correction circuit 15 performs gamma correction, and then sends it to the color difference matrix circuit 16.

The color difference matrix circuit 16 converts the R, G, B signals into color difference signals (RY signals, BY signals), and the color subcarrier modulation circuit 17 modulates the color subcarriers by the color difference signals. Create a digital carrier color signal. Then, the D / A conversion circuit 18 converts the digital color signal into an analog carrier color signal and outputs it.

[0010]

However, in the above-mentioned conventional video signal processing, the suppression of the color false signal is carried out by the horizontal band limiting filter, but the following problems occur because of the fixed band filter. was there.

(1) A large-scale high-order filter is required to remove the edge component of the input signal. (2) If the band is not narrow enough, a false color signal will be recognized. (3) Even in the optical system, a sufficient low-pass filter (optical low-pass filter) is required. This reduces the sharpness of the luminance signal.

It is an object of the present invention to provide a video signal processing circuit which can solve such a problem.

[0013]

In order to solve the above-mentioned problems, a video signal processing circuit according to the present invention comprises a circuit for detecting a horizontal edge of an image and a color signal component depending on the output level of this circuit. And a filter whose pass band is changed.

The circuit for detecting the horizontal edge of the image detects the edge based on the horizontal band-pass output of the color signal component. Further, the filter has a first path for passing pixels of the same color as it is and a second path for passing an average value of pixels of the same color before and after, and detects a horizontal edge of an image. The ratio of the second pass is increased as the output level of the second pass is increased.

Further, the filter is configured to pass only the signal of the first path until the output level of the circuit for detecting the horizontal edge of the image reaches a predetermined level.

[0016]

According to the present invention, the band of the color signal component changes according to the size of the horizontal edge of the image, so that it is possible to reduce the color false signal and widen the band of the color signal. Further, the pixels of the same color are allowed to pass through until the size of the horizontal edge of the image reaches a predetermined level, so that it is possible to suppress the effect of a large-amplitude edge that exceeds the predetermined level.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a block diagram of a video signal processing circuit to which the present invention is applied. Here, the parts corresponding to those in FIG. 9 are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the output of the A / D conversion circuit 3 and the signals delayed by the 1-line delay circuits 4 and 5 are input to the edge detection circuit 19. Edge detection circuit 19
Detects the horizontal edge (vertical edge) of the image from these input signals and outputs the control signal to the variable coefficient + fixed coefficient low pass filter 20. The variable coefficient + fixed coefficient low-pass filter 20 is composed of a variable coefficient low-pass filter configured to change the coefficient according to a control signal and a fixed coefficient low-pass filter as in the conventional example, and controls the coefficient of the variable coefficient low-pass filter. The characteristics are changed according to the signal, and filtering is performed with different characteristics between the edge portion and the flat portion of the image.

FIG. 2 shows an example of the edge detection circuit 19.
Here, 0H, 1H, and 2H are the output signal of the A / D conversion circuit 3, the output signal of the 1-line delay circuit 4, and the output signal of the 1-line delay circuit 5, respectively.

First, a signal having a high correlation in the vertical direction is generated by passing through the low-pass filter 21 in the vertical direction. Then, the horizontal edge of the image is detected by passing through the horizontal band pass filter 22. Note that this filter portion may be a combination of a bandpass filter in the horizontal direction first and a lowpass filter in the vertical direction next. It may also be configured by a two-dimensional filter.

The absolute value of the horizontal edge of the image detected by the bandpass filter 22 is detected by the absolute value circuit 23, and the control signal is generated by the non-linear circuit 24.

FIG. 3 shows an example of the characteristics of the non-linear circuit 24. In this example, the coefficient control signal K is 0 until the edge amplitude reaches a predetermined level, and when the edge amplitude becomes larger and exceeds this level, it gradually increases as the edge amplitude increases, and the edge amplitude becomes maximum. Sometimes the coefficient control signal K is one.

FIG. 4 shows the structure of the low-pass filter 20. Output signal of A / D conversion circuit 3 and 1-line delay circuit 5
The output signals of 1 are added by the adder 31 and then input to the switch 32. On the other hand, the output signal of the 1-line delay circuit 4 is directly input to the switch 33. Switch 3
2 and 33 are switched so that the CR line signal is input to the adder 34 and the CB line signal is input to the adder 35. Then, the low-pass filters 36 and 37 add the adders 34 and 35 based on the control signal from the edge detection circuit 19.
The signals of the CR line and CB line input from are filtered and output. Note that this circuit is basically the same as the low-pass filter 12 of FIG. 9 except that the coefficients of the low-pass filters 36 and 37 are variable according to the control signal from the edge detection circuit 19.

FIG. 5 shows an example of the variable coefficient low pass filter. In this figure, when the pixel is applied to the edge portion, K increases, so that the average level of two pixels before and after passing through the lower path (pixels of the same color filter are separated by two pixels) becomes dominant. On the contrary, K is small except at the edge, and the level of the pixel passing through the upper path is dominant. The low pass filters 36 and 37 of FIG. 4 are composed of such a variable coefficient low pass filter and a fixed coefficient low pass filter connected in cascade.

FIG. 6 shows an explanation of the operation. The input signal shown in (a) indicates the repetition of S1 and S2, and ◯ indicates S1.
System, x represents S2 system. In the flat part of the image, S1,
The level of both S2 is 1, but the level of S1 is 2 when an edge in the horizontal direction is imaged.

In the conventional fixed coefficient low-pass filter,
The impulse response of this input signal spreads and becomes a color false signal. On the other hand, in the present embodiment, as shown in (b), the vertical edge component is extracted by the horizontal bandpass filter. Note that (b) shows only the S1 system (the S2 system does not affect the operation because the level is constant). Next, as shown in (c), the absolute value circuit folds back the positive component. Then, the signal of this absolute value is input to the coefficient control circuit. This non-linear characteristic is shown in (d) when the output of this absolute value circuit is input to the variable coefficient filter because the coefficient control signal changes between the edge amplitudes of level 1 and level 2 as shown in FIG. Such a coefficient control signal is obtained. As a result, the pixel at the edge portion is completely changed to the average of the pixels before and after, so that the output of the variable coefficient filter is kept at 1 as shown in (e).

In other words, in the conventional example, the spread of the impulse response of the input signal is transmitted to the subsequent stage, but in the present embodiment, the edge part is changed by changing the coefficient of the filter by the signal detecting the horizontal edge of the image. The color false signal of can be completely suppressed.

The variable coefficient low-pass filter may be generally constructed as shown in FIG. Further, the present invention can be applied to a general single-chip color video camera that creates a color signal component from a pixel difference signal in the horizontal direction.

[0029]

As described in detail above, according to the present invention, the following effects (1) to (3) are exhibited. (1) Reduction of false color signals and wide band of color signals can be realized.

(2) It is possible to effectively suppress the influence of a large-amplitude edge of the false color signal. (3) Since the band of the optical low-pass filter can be widened, the sharpness of the luminance signal is improved.

[Brief description of drawings]

FIG. 1 is a signal processing block diagram of a CCD color camera to which the present invention is applied.

FIG. 2 is a block diagram showing an example of the horizontal edge detection circuit of FIG.

FIG. 3 is a diagram showing an example of characteristics of the nonlinear circuit of FIG.

FIG. 4 is a block showing an example of a low pass filter of FIG.

5 is a block showing an example of a variable coefficient filter in FIG.

FIG. 6 is a diagram showing a waveform of each part with respect to a horizontal edge signal.

FIG. 7 is a diagram showing an example of a non-linear characteristic with respect to FIG.

FIG. 8 is a diagram showing a general configuration of a variable coefficient filter.

FIG. 9 is a signal processing block diagram of a conventional CCD color camera.

10 is a diagram showing an arrangement of color filters on the CCD image sensor of FIG.

[Explanation of symbols]

19 ... Edge detection circuit, 20 ... Variable coefficient + fixed coefficient low-pass filter, 22 ... Horizontal pan-pass filter

Claims (4)

[Claims] 1. A video signal processing circuit comprising: a circuit for detecting a horizontal edge of an image; and a filter in which a pass band of a color signal component changes according to an output level of the circuit. 2. A video signal processing circuit according to claim 1, wherein a horizontal edge of an image is detected based on a horizontal band-pass output of a color signal component. 3. The filter has a first pass for passing pixels of the same color as it is, and a second pass for passing an average value of pixels of the same color before and after, and a horizontal edge of an image. 3. The video signal processing circuit according to claim 1, wherein the ratio of the second path is increased as the output level of the detecting circuit increases. 4. The video signal processing circuit according to claim 3, wherein the filter passes only the signal of the first path until the output level of the circuit for detecting the horizontal edge of the image reaches a predetermined level.