JPH0447792A - Color noise reduction circuit - Google Patents

Abstract

PURPOSE:To reduce noise included in a color difference signal with a narrow frequency band without generation of unsharpened contour and color slurring or the like even when a signal amplitude is small by detecting the contour of the color difference signal and a luminance signal and controlling a noise reduction circuit 11 in response to the result of detection. CONSTITUTION:A contour part of a luminance signal corresponds to a contour of a color difference signal and its frequency band is wide, then even when the signal amplitude of the color difference signal is small, a contour detection circuit 15 is operated to detect the contour of the luminance signal. Even when the amplitude of the luminance signal is small, if the amplitude of the color difference is somewhat large, a contour detection circuit 13 is operated to detect the contour part of the color difference signal. Thus, the contour part of the usual color difference signal is able to be detected, a noise reduction circuit 11 is operated to reduce noise at a flat portion only. Thus, the generation of unsharpened contour and color slurring or the like is less.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to video signal processing for television receivers, etc.
In particular, the present invention relates to a color noise reduction device suitable for reducing noise in color difference signals.

[Conventional technology]

As a conventional technique, there is a configuration described in Japanese Patent Application Laid-open No. 10087/1987.

A diagram of this circuit configuration is shown in FIG. 5, and waveforms of each part are shown in FIG.

In FIG. 3, the contour detection circuit %8 is a limiter detection circuit, and is a circuit that outputs a signal corresponding to the contour of the video signal.

The operation shown in FIG. 3 will be explained below using FIG. 4.

The video signal input through the video signal input terminal 1 includes a fourth
The noise components shown in Figure a (jaggies in the figure) are superimposed. Since this noise component is a high-frequency component of the video signal, first, the high-frequency component is separated by passing it through the Neubus filter 2 shown in FIG. 3, and then the noise component is extracted by an amplifier 5 and a limiter 4. .

However, since this extracted noise component also includes the contour component of the video signal, if this signal is added to the input video signal as a canceling noise signal by the polarity inversion amplifier circuit 5 and the attenuator (ATT) 6K, The outline becomes dull.

In order to eliminate this alignment, a contour detection circuit 8t is provided to detect the contour of the video signal, control the changeover switch 7 with the detection signal, and cancel the noise in the contour where noise is less noticeable. In addition to stopping the addition of the noise signal to the input video signal (or reducing the amount of addition), this arrangement eliminates the distortion of the contour of the video signal.

Generally speaking, the circuit shown in FIG. 5 can be roughly divided into two circuits, as shown in FIG. 5. In the circuit shown in FIG.

However, when the frequency band of the signal component is wide like the video signal handled in this case, the contour detection signal d can be used to select the changeover switch 7 in Fig. 3 or the noise reduction t in Fig. 5.
Even with t-control, the difference in control timing is very small and does not pose a problem. However, if the same system is used for the color difference signal after demodulating the color signal, the color difference signal will have an extremely narrow band (
500KHz~1.5MH! Therefore, when the amplitude of the signal is small, as shown in Figure 6, there are cases where the contour cannot be detected or the control timing is greatly shifted, and as a result, the contour may be distorted by one color. There was a problem in that problems such as the following occurred.

[Problem to be solved by the invention]

As described above, in the conventional technology, when the frequency band of the video signal is narrow like a color difference signal, especially when the signal amplitude is small, the noise reduction operation is not effective.

There was a problem in that the contours were dull, color deviations, etc. occurred.

The present invention solves the above-mentioned problems of the prior art, and eliminates noise contained in a color difference signal with a narrow frequency band, such as dull contours and colors, even when the signal amplitude of the color difference signal is small. It is an object of the present invention to provide a noise reduction device capable of reducing noise without causing deviation or the like.

[Means to solve the problem]

In order to achieve the above object, the present invention detects the contours of two signals, a color difference signal and a luminance signal, which are signal components of a video signal, and controls a noise reduction circuit according to the detection results. It is something.

[Effect]

The contour of the luminance signal basically corresponds to the contour of the color difference signal, and its frequency band is wide, so even if the signal amplitude of the color difference signal is small, it is difficult to detect the contour of the brightness signal. 1 contour detection circuit operates. Further, even when the signal amplitude of the luminance signal is small, if the signal amplitude of the color difference signal is large to some extent, the contour detection circuit operates to detect the contour of the color difference signal. As a result, the contour part of the normal color difference signal can be detected, and the noise reduction circuit operates to reduce noise only in the flat part, so the noise reduction operation can cause the contour part of the color difference signal to become dull, color sagging, etc. occurrence is low.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a waveform diagram showing waveforms of various signals in FIG. 1.

In FIG. 1, when the color difference signal K is input, the composite contour detection signal 0 is generated by the color difference signal contour detection circuit 15,
Sum of output waveforms of luminance signal contour detection circuit 14 (L+N)
The noise reduction circuit 11 is controlled by this composite contour detection signal O, and a color difference signal P is obtained.

According to the present embodiment, it is possible to reduce the noise signal component only in the flat portion of the color difference signal without an amplitude change without damaging the contour signal component of the input color difference signal.

In FIG. 1, the color difference signal K and the luminance signal Mi are each digital signals, and the color difference signal contour detection circuit 14, the luminance signal contour detection circuit 15, the contour detection signal synthesis circuit 16, and the noise reduction circuit 171. Each of them may be configured with a digital circuit.

〔Effect of the invention〕

According to the present invention, it is possible to reduce noise contained in a color difference signal with a narrow frequency band without causing dulling of contours, color shift, etc. even when the signal amplitude of the color difference signal is small. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a waveform diagram showing waveforms of various signals in FIG. 1, FIG. 5 is a block diagram showing a conventional noise reduction device, and FIG. The figure is a waveform diagram showing the waveform of each part signal in Figure 4, Figure 5 is a block diagram showing a simplified circuit of Figure 6, Figure 6 is a narrow band, small amplitude video signal input as an input signal. A waveform diagram showing the waveforms of each part signal in FIG. 4 when
It is. 1... Video signal input terminal 2... Bypass filter 5... Amplifier 4... Limiter 5... Polarity inversion amplifier circuit 6... Attenuator 7... Changeover switch 8... Contour detection Circuit 9... Adder 10... Video signal output terminal 11... Noise reduction circuit 12... Color difference signal input terminal 15... Color difference signal contour detection circuit 14... Luminance signal input terminal 15. ... Luminance signal contour detection circuit 16 ... Contour detection signal synthesis circuit 17 ... Color difference signal output terminal.

Claims (1)

[Claims] 1. In a color noise reduction device that reduces noise contained in a color difference signal and a luminance signal obtained as a video signal, the color difference signal is input, and the contour part of the color difference signal is input. a first contour detection circuit that detects the contour and outputs a first detection signal indicating the detected contour; a second contour detection circuit that outputs a second detection signal indicating a contour; A color noise reduction device comprising: a noise reduction circuit that reduces and outputs noise contained in portions other than portions corresponding to contour portions indicated by respective detection signals. 2. In the color noise reduction device according to claim 1, the color difference signal and the luminance signal are each digital signals, and the first and second contour detection circuits and the noise reduction circuit each include a digital circuit. A color noise reduction device characterized by: