JPS6112192A - Circuit for reducing noises of color difference signal - Google Patents

Abstract

PURPOSE:To reduce noise by comparing the maximum level of plural color difference signals with plural reference voltages, generating control signals corresponding to plural color difference signals and setting up plural color difference signals, then making each color difference independent. CONSTITUTION:A level detection means is constituted of clamp circuits 21a and 21b, limiter amplifiers 22a and 22b and full-wave shaping circuits 25a and 25b. The level detection means detects levels of plural arriving color difference signals, and the maximum level is selected among the detected signals by a selection circuit 26. comparators 27a and 27b have plural reference voltages corresponding to plural difference signals, compare plural reference voltages with the selected level detection signal, and generate control signals in correspondence to plural color difference signals. These control signals are supplied to analog switches 24a and 24b, which execute the amplitude suppression of corresponding color difference signals in accordance with plural control signals.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color difference signal noise reduction circuit, and more particularly to a color difference signal noise reduction circuit that reduces small amplitude noise contained in the color difference signal.

2. Description of the Related Art Conventionally, some video output circuits of color video cameras are provided with noise reduction circuits for color difference signals.

FIG. 3 shows an example of a conventional color difference signal noise reduction circuit.

In the figure, color difference signals R-Y and B-Y are input to terminals 1 and 2, respectively, and subcarriers are input to terminals 3 and 4, respectively.

The R-Y modulator 5 performs balanced modulation of the subcarrier with the color difference signal R-Y, and the obtained modulated wave signal is supplied to the mixer 7 via the gain control circuit 6, where it is modulated via the gain control circuit 9. The chroma signal is added and mixed with the modulated wave signal from the BY modulator 8 supplied by the chroma signal, and the chroma signal is supplied to the chroma gain control circuit 10. In addition, the R-Y modulator 5. The modulated wave signals from the B-Y modulators 8 are detected by the detectors 11 and 12, respectively,
The respective detection outputs are added and mixed in a mixer 13 and then supplied to a low saturation detector 14.

The low saturation detector 14 generates a control signal and supplies it to the chroma control circuit 10 when the detected output is below a predetermined level. When the chroma gain control circuit 10 is supplied with the above control signal, it suppresses the amplitude of the chroma signal, and a chroma signal with low saturation suppression is output from the terminal 15. As a result, the amplitude of the chroma signal is suppressed in the range surrounded by the solid line (■) in FIG. 4, and color errors on a nearly achromatic screen are eliminated.

Problems to be Solved by the Invention In the conventional circuit, since the amplitude of the chroma signal is suppressed, the color difference signals R-Y, ! It is impossible to reduce the noise of each of 3-Y independently. However, in a color video camera, for example, the color difference signals R, -Y, and BY are processed in independent processes, and the nature of the noise contained in each of the color difference signals R-Y and BY is different. When these noise components have different magnitudes, the conventional circuit has a problem in that it is not possible to control the gain of the chroma signal so as to optimally reduce each of the two noise components.

Further, the color difference vector in which the components of the color difference signals R-Y and B-Y are approximately equal is on the R-Y axis in FIG.

It has a direction of approximately 45 degrees with respect to the B and Y axes, but in the conventional circuit, as shown by the solid line ■, the range in which the above color difference vector is suppressed is narrow, and the noise reduction effect is low. . Furthermore, an R-Y modulator 5. If the balance of the subcarriers supplied to each of the BLY modulators 8 is shifted, a DC offset of the modulated wave signal outputted from each occurs, so that the low-level saturation detector 14 detects a low-level signal below a predetermined level. The problem was that it became unstable.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a color difference signal noise reduction circuit that solves the above problems.

Means and Function for Solving Problems The present invention provides level detection means for detecting the level of each of a plurality of incoming color difference signals, and a level detection signal of the maximum level among the level detection signals of each of the plurality of color difference signals. a selection means for selecting, a plurality of reference potentials corresponding to each of the plurality of color difference signals, and comparing each of the plurality of reference potentials and the selected level detection signal to generate a control signal corresponding to each of the plurality of color difference signals; The apparatus is comprised of a comparing means for suppressing a plurality of control signals, and an amplitude controlling means for suppressing the amplitude of a corresponding color difference signal in accordance with a plurality of control signals, and an embodiment thereof will be described with reference to FIG. 1 and subsequent figures.

Embodiment FIG. 1 shows a block diagram of an embodiment of the circuit of the present invention. In the figure, a color difference signal RY is input to a terminal 20a, and a color difference signal B-Y is input to a terminal 20b. The color difference signal R-Y from the terminal 20a is supplied to the clamp circuit 21a and clamped, and then sent to the limiter amplifier 22a and the attenuator 23.
a and analog switch 2.4a, respectively. The limiter amplifier 22a removes large components of the color difference signal R-Y supplied from the clamp circuit 21a that are unnecessary for clamp processing and noise reduction processing, and amplifies and outputs only the necessary components. The output signal of the limiter amplifier 22a is fed back to the clamp circuit 21a, and the output signal of the limiter amplifier 22a is fed back to the clamp circuit 21a.
clamps the incoming color difference signal RY in response to the feedback described above, and outputs the color difference signal RY without DC offset. Further, the output signal of the limiter amplifier 22a is supplied to a double-wave rectifier 25a, where it is double-wave rectified to obtain a rectified signal.

Similarly, the color difference signal B-Y from the terminal 20b is clamped by the clamp circuit 21b and then sent to the limiter amplifier 2.
2b, an attenuator 23b, and an analog switch 24b, and a signal obtained by level-limiting and amplifying the color difference signal B-Y with a limiter amplifier 22b is fed back to the limiter amplifier 22b and is also supplied to a double-wave rectifier 25b. . The above clamp circuits 21a, 21b, limiter amplifier 2
2a.

The 22b1 double-wave rectifier circuits 25a and 25b constitute a level detection means.

The rectified signals output from each of the double-wave rectifiers 25a and 25b are supplied to a selection circuit 26. The selection circuit 26 is like an OR circuit having a diode configuration, and selects and extracts the rectified I/H signal having the higher voltage from among the two rectified signals. The rectified signal taken out by the selection circuit 26 is sent to comparators 27a and 27.
b supplied to people. A reference potential Vref+ is supplied to the comparator 27a from a terminal 28a, and the rectified signal is compared with the reference potential Vrefl to generate a control signal that becomes, for example, H level when the rectified signal is large, and L level when it is small. and is supplied to the analog switch 24a. Similarly, the comparator 271) sends the rectified signal to the terminal 28b.
When the rectified signal is large, a 1-level control signal is generated, and when it is small, a 1-level control signal is generated and supplied to the analog switch 24b.

The attenuator 23a receives the color difference signal R- from the clamp circuit 21a.
Y is attenuated by a predetermined amount and supplied to the analog switch 24a. The analog switch 24a takes out the color difference signal RY from the clamp circuit 21a when the control signal from the comparator 27a is 1 level, and takes out the attenuated color difference signal RY from the attenuator 23a when the control signal is at L level. Take it out and output it from terminal 29a. Similarly, the analog switch 241) takes out the color difference signal B-Y from the clamp circuit 21b when the control signal from the comparator 27b is at H level, and takes out the attenuated color difference signal from the attenuator 23b when the control signal is at L level. B-Y is taken out and output from the terminal 29b. The above-mentioned attenuator 23a.

23b and analog switches 24a and 24b constitute amplitude control means.

Figures 2 (A) to (D) show the suppression degree characteristics of color difference signals of the above circuit.
). In the figure, the signal suppression thresholds indicated by the dashed line and the dashed double dotted line are the reference potential Vr of the comparators 27a and 27b.
This is equivalent to converting ef l , Vret' 2 into the amplitude of the input color difference signal. For example, as shown in FIG. 2(A), if the suppression threshold of the color difference signal R-Y shown by the dashed-dotted line [a is set to be larger than the suppression threshold of the color-difference signal B-Y shown by the dashed-dotted line ma, A color difference vector 31 having an absolute value larger than the range of 1[1a and smaller than the range of the two-dot chain line 11a has its R- and Y components 31a suppressed, but its B-Y component 31b is not suppressed. Therefore, the R-Y component 32a obtained by suppression and the above B-, Y components 31
A color difference vector 32 is generated by combining with b.

Further, as shown in FIG. 2(B), the suppression threshold of the color difference signal RY shown by the two-dot chain line Ull is the same as the color difference signal B shown by the two-dot chain line mb.
- When set to be smaller than the suppression threshold of Y, a color difference vector 33 whose absolute value is smaller than the range of the dashed-dotted line mb and further than the dashed-double line mb has only its B-Y component suppressed. As a result, a color difference vector 34 is obtained.

The suppression thresholds of the above color difference signals R-Y and B-Y are determined by the comparators 27a and 27b, respectively.
' l and Vref 2 are varied, and are enlarged or reduced around the origin in the figure.

In addition, in FIG. 2(C), the part molecule va parallel to the R-Y axis of the suppression threshold of the color difference signal R-Y or B-Y is indicated by a solid line ■.
, rvb are the amplification degree of the limiter amplifier 22b and the reference potential V ref I of the comparators 27a and 27b, respectively.
By varying Vret 2, it is possible to move in the BY-axis direction as shown by the arrow in the figure.

In addition, a portion Va parallel to the BY axis of the suppression threshold of the color difference signal RY or BY shown by the solid line V in FIG. 2(D),
Vb is the amplification degree of the limiter amplifier 22a and the comparator 2.
Reference potentials Vfef + and Vre of 7a and 27b, respectively
By varying each of f2, as shown by the arrow in the figure, <
Can move in the RY axis direction.

Therefore, by varying the degree of amplification of each of the limiter amplifiers 22a and 22b, it is possible to vary the aspect ratio of the suppression threshold of the color difference signals RY and 'BY.

In this way, by varying the amplification degrees of the limiter amplifiers 22a and 22b and the reference potentials vrer I and Vref 2, it is possible to suppress and control the color difference signals RY and BY independently.

Furthermore, as shown in FIG. 2 (A>, (B)), the color difference signal R-
By independently setting the suppression thresholds for Y and B=Y, the direction of the color difference vector can be varied.For example, in a color video camera, the phase of the color difference signal is affected by its amplitude. If a phase error occurs in the color difference signal at times, it is also possible to correct the phase error.

Furthermore, when there is no need to change the direction of the color difference vector, the suppression thresholds for the color difference signals RY and BY are set to be the same.

Further, each of the color difference signals R-Y and B-Y is connected to a clamp circuit 21.
Since it is suppressed after being clamped by each of a and 21b, it is possible to prevent a suppression error from occurring due to a DC A hit, as in the conventional case.

Note that the circuit of the present invention is applicable not only to color video cameras but also to any other devices that process color difference signals. In addition to the color difference signals R-Y and B-Y, the color difference signal G-Y
Noise reduction may also be performed in the same manner for , and is not limited to the above embodiment.

Effects of the Invention As described above, the color difference signal noise reduction circuit according to the present invention has the following effects:
Level detection means for detecting the level of each of the plurality of incoming color difference signals; selection means for selecting the level detection signal of the maximum level among the level detection signals of each of the plurality of color difference signals; a comparison means having a plurality of corresponding reference potentials and generating a control signal corresponding to each of the plurality of color difference signals by comparing each of the plurality of reference potentials and the selected level detection signal; Since the configuration includes amplitude control means for suppressing the amplitude of the corresponding color difference signals, optimal noise reduction can be performed independently for each of the plurality of color difference signals, and DC offset does not occur in each color difference signal, reducing suppression errors. It has the advantage of being able to prevent the occurrence of color difference signals, and further correcting phase errors of small color difference signals.

[Brief explanation of drawings]

FIG. 1 is a block system diagram of one embodiment of the circuit of the present invention, and FIG.
1 is a characteristic diagram of the circuit shown in FIG. 1, FIG. 3 is a block diagram of an example of a conventional circuit, and FIG. 4 is a characteristic diagram of the circuit shown in FIG. 20a, 20b, 28a, 28b, 29a. 29b...Terminal, 21a, 21b...Clamp circuit, 22a, 22b-...Limiter amplifier, 23a, 2
3b...attenuator, 24a, 24b...analog switch 25a, 25b...double wave rectifier, 26...
- Selection circuit, 27a, 27b... comparator.

Claims (3)

[Claims] (1) Level detection means for detecting the level of each of the plurality of incoming color difference signals; selection means for selecting the level detection signal of the maximum level among the level detection signals of each of the plurality of color difference signals; a comparison means having a plurality of reference potentials corresponding to each of the signals and generating a control signal corresponding to each of the plurality of color difference signals by comparing each of the plurality of reference potentials with a selected level detection signal; 1. A noise reduction circuit for a color difference signal, comprising amplitude control means for suppressing the amplitude of a corresponding color difference signal in accordance with a control signal of the color difference signal. (2) The level detecting means is configured to clamp each of the plurality of color difference signals, perform level limiting amplification, and then perform dual wave rectification. Noise reduction circuit. (3) The amplitude control means is configured to switch and output a signal obtained by attenuating each of the plurality of color difference signals and each of the plurality of color difference signals in accordance with each of the plurality of control signals. The color difference signal noise reduction circuit according to item 1.