JPS6245285A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To effectively reduce noise without giving feeling of disorder on a reproducing picture by controlling the volume to be base-clipped while reacting corresponding to a video state, for example, illuminance, electric field or luminance difference. CONSTITUTION:From a video signal taken out from an image pickup element 1, a luminance signal Y, color difference signals R-YL and B-YL are separated and outputted, being inputted to an encoder circuit 4. The signal Y inputted to the circuit 4, on which various signal processes are applied at a signal process circuit 8, is inputted to a mixing circuit 13. On the other hand, signals R-YL and B-YL are inputted to the circuit 13 through modulation circuits 9 and 10, an adder 11 and a base clipping circuit 12, and are mixed with the signal Y to generate an NYSC signal. At such a case, the volume of the base clipping in the circuit 12 is controlled while reacting corresponding to a controlled voltage impressed on a terminal 16, that is, the illuminance, the electric field or the luminance difference, reducing the noise.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a video signal processing circuit for a video camera, etc.
In particular, the present invention relates to a signal processing circuit suitable for effectively reducing color noise or white noise.

[Background of the invention]

Conventionally, as an example of this type of noise reduction circuit, a video luminance signal is separated into a contour (high frequency) component corresponding to the contour part of the image and a flat (low frequency) component corresponding to the flat part of the image. After removing the noise component on the baseline by base clipping the 7 contours, the so-called base clip is mixed again with the flat signal to visually reduce the noise in the flat part of the playback screen. A circuit is known (Japanese Patent Publication No. 42-21269).

Here, we focus on the rattle noise that occurs in relatively noisy conditions, such as weak electric field to medium LD field in television signals, and relatively low-light conditions in video cameras, and if we try to significantly improve the noise, we will solve the problem described above. The base clip amount is also set to a large extent! However, as the situation moves to a strong electric field or high illuminance, that is, as the condition becomes relatively good, the signal itself is base-crimped. There was a problem in that the effect of the base clip became noticeable and the reproduced image felt visually strange, and the larger the amount of base clipping, the more unpleasant the feeling became.

This unnatural feeling refers to a phenomenon in which a contour signal is reproduced in the case of a luminance signal processing system, but details in flat areas of the image are lost, resulting in an unnatural image. On the other hand, in the color signal processing system, in order to improve color distortion in video cameras, etc., a base clip circuit may be installed in the color subcarrier signal generation path of the encoder circuit that generates NTSC signals, etc. , and the phenomenon in which a photographed image containing many low-chroma colors is reproduced as a faded image also feels strange.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing circuit that improves the problems of the prior art described above and effectively reduces noise without giving a sense of discomfort to reproduced images.

[Summary of the invention]

In order to achieve the above object, the present invention automatically controls the base clip filter of the base clip circuit according to various video situations. In other words, the AGC voltage that controls the gain of the AGC amplifier circuit that is generally installed in the front stage of the video signal processing circuit, or the voltage that changes with the video situation, such as the brightness signal, is used to control the base clip voltage under noisy video conditions. On the other hand, a strong electric field (
This is an automatic control system that automatically reduces the base clip effect (Brevision receiver) and high illuminance (video camera).

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIGS. 1 and 2. This embodiment is an example for reducing color noise in a video camera.

In FIG. 1, a video signal taken out from an image sensor 1 is inputted to a process circuit B via a preamplifier circuit (preamplifier) 2 and an AGC amplifier circuit 5.

In the process circuit 6, known signal processing such as gamma correction and arithmetic processing is performed, and the luminance signal Y1 color difference signal RYL, B
-Yt are respectively separated and output and input to an encoder circuit 4 that generates an NTSC signal.

On the other hand, the luminance signal Y is also supplied to the AGC detection and amplification circuit 7, and the AGC voltage is generated by the circuit 7.
Generally, in a video camera, the gain is controlled by applying it to the control terminal 15 of the amplifier circuit 5.Although not shown in the figure, first, when the amount of light incident on the lens is relatively small (low to medium illuminance), As the incident light t becomes thicker, the AGC width width circuit 5 applies a control voltage to the AGC amplifier circuit 50 control terminal 15 such that the gain decreases from the maximum gain state,
After completing the predetermined gain control range, when the illuminance of the subject becomes higher and the entrance light to the lens becomes narrower, the iris mechanism is controlled to gradually close from the open state and image capture is performed. The amount of light incident on the element 1 is controlled. In this way, the level of the video signal input to the process circuit B is controlled to a predetermined rated level over a wide range of the amount of incident light.

The luminance signal Y input to the encoder circuit 4 is processed by a signal processing circuit 8 into a white clip and a black clip 7.

The signal is subjected to various signal processing such as blanking and addition of a synchronization signal, and then input to the mixing circuit 16. On the other hand, the color difference signal R-YLIB-YL input to the encoder circuit 4 is transmitted to the modulation circuit 9,
At step 10, balanced modulation is performed using subcarrier signals each having a phase different by 90°, and an adder circuit 11 calculates 2Il. The color subcarrier No. 1g obtained at the output of the adder circuit 11 is input to a mixer circuit 13 through a so-called paster rip circuit 12 which compresses the output signal as the input level becomes smaller. is combined with the luminance signal Y to generate the N'rSC signal. Note that in the base clip circuit 12, the paster IJ knob is controlled in response to a control voltage applied to the terminal 16. In this example, the AGC voltage obtained at the output of the EC detection amplifier circuit 7 is converted by the control voltage conversion circuit 14 to
The lower the illuminance area, the larger the base clip amount, and as the illuminance increases, the voltage is appropriately changed and applied to the control terminal 16 so that the base clip lid becomes smaller.

Next, the operating principle of the present invention will be explained using the input/output characteristic diagram of the base clip circuit shown in FIG. As described above, the base clip circuit 12 is installed in the color subcarrier signal generation path to reduce color noise. (α) in the figure shows the input/output characteristics of the base clip circuit, into which the illustrated color subcarrier signal is input. This figure is a schematic diagram at low illuminance and shows relatively large noise. As is clear from the figure, the highly saturated color subcarrier signal B is relatively not compressed very much;
The noise C1, which is approximately equivalent to the base clip lt (Cr), is suppressed and the forest quality is improved. Of course, the low chroma color subcarrier signal A is also suppressed at the same time, but it is already covered with noise and there is no discomfort in the reproduced image. If we consider the case where the illuminance gradually increases from this state, the noise C will decrease accordingly, so here A
If the base clip IT (Cr) is controlled and reduced by GC electromagnetic correction, the low chroma color subcarrier signal A will be effectively reproduced, and reproduction outdoors with high illuminance and low chroma colors will be unnatural. does not occur. Figure 2 (The smell is base clip circuit 1
This is a diagram illustrating the input/output characteristics of No. 2 in a different way.

That is, the characteristics (1) to (2) represent the manner in which the degree of compression at the output level is controlled by the control voltage with respect to the directly input signal level. That is,
For example, when the illuminance is low, the base clip control voltage is operated according to the characteristic (2), and when the illuminance is high, the base clip control voltage is controlled in response to the pressure.

As explained above, according to this embodiment, it is possible to improve color noise in low illumination while also improving the unnatural phenomenon of saturation reduction in low-chroma images that often occurs under high illumination, especially outdoors. can.

FIG. 6 (α) is shown in the embodiment of FIG. 1, ? 1ill @
1 is a specific example of a voltage conversion circuit. In general, the AGC voltage shows a predetermined transition from the lens closed state in response to changes in illuminance. FIG. 3(b) shows an outline of the change from the voltage V when the lens is closed to the AGC-ffi pressure VA when the gain attenuation ends. The AGC voltage shown in the figure is applied to the terminal 15, and when the AGC voltage is VB, the transistor Q1 is turned off, and a control voltage determined by the ratio of the resistors R2 and R5 is generated at the terminal 16.

On the other hand, when the voltage is higher than Vc, the transistor Q1 is completely turned on (saturated operation), and a control voltage of approximately 1B is generated. Therefore, a voltage that changes in R2 and R3 in the range of Vcc.□ to Va can be obtained depending on the illuminance, and by appropriately setting Ro, VB, R2, and R3, a desired base clip control voltage can be obtained.

FIG. 4 is a diagram showing a second embodiment, in which the base clip circuit 12 is controlled by a luminance of 4 g (tons). The brightness 1 signal Y obtained at the output of the process circuit B is the first
As explained in the example of AC, Ci′ll1l @3
However, the amplitude value remains constant even at very low illuminance.

This luminance value (g), amplitude value, and polarity.

The voltage is converted by the voltage conversion circuit 14 to a DC operating point, etc., and applied to the terminal 16. The main point of this embodiment is to increase the base clipping effect in dark areas within the same group even under relatively high illuminance, and to make it smaller in bright areas, thereby reducing noticeable noise in dark areas. Of course, AGC does not operate (maximum gain condition) at any low illuminance, as the amount of incident light decreases, the luminance signal obtained at terminal 15 also decreases, and the pace crimp effect on the entire screen increases, causing visual acuity. The improvement effect is also significant.

FIG. 5 is similar to FIG. 4 in that it is controlled by the f4 degree signal (G), but is configured so that the fi4 degree Ig signal is detected by the AGCM width circuit 5 and D. By the way, the brightness signal level of this brightness signal changes according to the illuminance even in the light 1 important area corresponding to the AGC system. Therefore, if such a luminance signal is used as the base clip control pressure (-), the control effect accompanying the change in AGC amplitude pressure (illuminance) in the embodiment of the present invention in FIG. Even within the same image as described above, an effect is obtained as if the effect of changing the base clip according to the brightness and darkness was weighted.

The embodiments of the present invention have been described above from the perspective of reducing color noise in video cameras. Although not described in detail in the text, the base clipping circuit used as a means for reducing white noise with a luminance of 100, as in the above-mentioned known example, can be used as a means for reducing the amount of base clipping in response to changes in illuminance or luminance signal, as in the present invention. It goes without saying that a control configuration may also be used.

〔Effect of the invention〕

As explained above, according to the present invention, white noise can be reduced without significantly losing definition in flat areas of the image, and the saturation of low-chroma UEJ images, such as those seen outdoors, can be significantly reduced. There is an effect that the color noise can be effectively reduced without causing any discomfort, that is, the noise can be effectively reduced without causing any discomfort in the reproduced image.

[Brief explanation of drawings]

Fig. 1 is a block configuration diagram of a signal processing circuit showing an example of the present invention, Fig. 2 is an input/output characteristic diagram of a base clip circuit for explaining the present invention in detail, and Fig. 3 (α), (
b) is a circuit diagram showing a specific example of the voltage conversion circuit used in the present invention and a characteristic diagram showing the relationship between illuminance and AGC pressure;
FIGS. 4 and 5 show the second embodiment of the present invention. FIG. 7 is a block configuration diagram showing main parts of a third embodiment. 1... Imaging probe, 2. Preamplifier circuit, 3.
Video signal processing circuit, 4...engine/coder circuit, 5...π
℃ amplifier circuit, 6...process circuit, 7...A
GC'M pressure detection amplifier circuit, 8... Luminance signal processing circuit, 9, 10... Modulation circuit, 1
DESCRIPTION OF SYMBOLS 1... Addition circuit, 12... Base clip circuit, 16... Mixing circuit, 14... Control voltage conversion circuit.

Claims (1)

[Claims] 1. In a signal processing circuit that base clips a video signal such as a television signal (for example, a color carrier signal or an image contour signal component) to reduce color noise and white noise,
The amount of base clipping can be adjusted depending on the image condition, e.g. illuminance, electric field, etc.
A video signal processing circuit that performs control in response to brightness (brightness) differences. 2. A video/signal processing circuit according to claim 4, characterized in that the amount of base clipping is controlled in response to an AGC voltage. 3. The video signal processing circuit according to claim 1, wherein the amount of base clipping is controlled in response to a difference in brightness of a luminance signal.