JPH04273679A - Noise eliminating device - Google Patents

Abstract

PURPOSE:To effectively eliminate noise of a chrominance signal by utilizing a YC separator circuit in the noise eliminating device used for a video disk or the like. CONSTITUTION:A luminance signal being an output of a YC separator circuit 2 employing a comb-line filter is given to a noise elimination circuit 3, in which a noise of a carrier chrominance signal band is eliminated. The output is added to the carrier chrominance signal obtained from the YC separator circuit 2 at an adder circuit to obtain a voideo signal whose chrominance signal S/N is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removal device used to improve the S/N ratio of a video signal of a video reproducing device such as a video disc player.

0002

2. Description of the Related Art In recent years, there has been a demand for higher image quality in equipment that handles video signals, such as video discs and VTRs, and there has been an increasing demand for noise removal techniques to improve the S/N ratio.

[0003] Particularly in video disc players, since the reproduced video signal contains cross-modulation noise of the audio FM signal, a noise removal device is essential to remove this noise.

[0004] Conventional noise removal devices include "Optical Discs and Video Discs" (edited by Shokodo, Television Society),
pp. 53-54).

[0005] A conventional noise removal device will be explained below. FIG. 4 is a block diagram showing the configuration of this conventional noise removal device. In FIG. 4, a video signal is input to a noise removal circuit 10 composed of a bandpass filter 11, a limiter 12, and a subtracter 13. The video signal in this case is a composite signal including a color carrier wave. By the way, the playback signal of a laser disc player includes audio F.
Contains the cross-modulation component of the M signal, and its frequency is approximately 2
．． It is 5MHz. Therefore, a bandpass filter 11 extracts signals near this frequency. Next, this signal is passed through a limiter only when its level is low, and its output is subtracted from the original signal. As a result, only low-level signals among signals near 2.5 MHz included in the video signal are removed, so that noise can be removed without degrading image quality. At this time, not only noise due to cross modulation but also disk noise around 2.5MHz and laser pickup noise are removed at the same time, and the S
/N is improved.

[0006] In addition to the composite signal, component signal output is also desired as the video signal output. Therefore, the video signal from which noise has been removed is separated into a luminance signal and a carrier color signal by a YC separation circuit 14 and output.

[0007]

However, with the above conventional configuration, it is difficult to effectively improve the S/N ratio of color signals. The reason for this will be explained next. Since the color signal is processed as a carrier color signal, its center frequency is N
In the case of a TSC signal, it is 3.58 MHz. Therefore, in the conventional configuration, the center passband of the bandpass filter 11 is set to 3.
．． Must be set to 58MHz. However, in such a configuration, the output of the bandpass filter 11 is the carrier color signal itself, and if this signal is passed through the limiter circuit and subtracted from the original signal by the subtracter 13, the light colors will be canceled and disappear. It cannot be used as a noise removal device.

The present invention solves the above-mentioned conventional problems, and aims to provide a noise removal device that can also remove noise from a carrier color signal.

[0009]

[Means for Solving the Problems] To achieve this object, the noise removal device of the present invention includes a YC separation circuit using a comb filter that separates an input video signal into a carrier color signal and a luminance signal; a noise removal circuit that removes noise in the carrier color signal band of the luminance signal separated by the YC separation circuit; and an output of the carrier color signal obtained by separation by the YC separation circuit and an output of the noise removal circuit. and an addition circuit that adds the.

0010

[Operation] With the above-described configuration, the present invention removes noise in the carrier color signal band of the luminance signal output from the YC separation circuit using a comb filter, and removes the noise in the carrier color signal band of the luminance signal and the YC separation circuit. A color signal with an improved S/N ratio is obtained by adding the carrier color signal separated by the color signal.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a noise removal device in a first embodiment of the present invention.

The video signal containing the carrier color signal is separated into a luminance signal 8 and a carrier color signal 9 by a YC separation circuit 2 using a comb filter. Luminance signal 8 is passed through bandpass filter 4
, a limiter 5, and a subtracter 6.
The output is added to the carrier color signal 9 by an adder circuit 7 and output as a composite signal.

In the noise removal circuit 3 , a signal in the chrominance signal band of the input luminance signal 8 is extracted by a bandpass filter 4 . Next, only when the level of this signal is low, it is passed through the limiter circuit 5 and subtracted from the input signal. As a result, a signal with a small level within the color signal band of the input signal is removed as an output signal, and a signal with an improved S/N ratio is obtained.

The above operation will be explained in more detail with reference to FIG. FIG. 3 expresses the spectrum of a video signal including a carrier color signal using two-dimensional frequencies. Figure 3 (a
) shows the spectrum of the luminance signal 8 and carrier color signal 9 separated by the YC separation circuit 2. The horizontal axis is the horizontal frequency,
The vertical axis represents vertical frequency. Since the noise removal circuit 3 described above removes the noise in the horizontal carrier color signal band of the "luminance signal" shown in FIG. 3(a), the noise in the frequency domain shown by diagonal lines is removed. become. In other words, the shaded portion represents the frequency region of the "noise-removed luminance signal" of the luminance signal.

Therefore, in the composite signal obtained at the output of the adder circuit 7, the noise of the signal in the shaded frequency region of the entire band is reduced.

Next, the S/N of the color signal when this composite signal is viewed on a television monitor is shown in FIG. 3(b).
). Many monitors use bandpass filters to separate carrier color signals and luminance signals. When a carrier color signal and a luminance signal are separated by a bandpass filter, they are separated into a "luminance signal" and a "carrier color signal extracted by a bandpass filter" as shown in (b). As can be seen from this figure, in this case, the "noise-removed luminance signal" area indicated by diagonal lines is processed as a carrier color signal. Therefore, according to the configuration of the present invention, since the S/N in this area is improved, the color signal S/N on the monitor is improved.

As described above, according to this embodiment, the S/N of the color signal on the monitor can be improved by using the YC separation circuit and providing a noise removal circuit for the luminance signal output.

Note that the passband of the bandpass filter 4 does not necessarily need to be set only to the color signal band; therefore, by widening the band to frequencies where interference due to cross-modulation exists, cross-modulation can also be removed at the same time.

FIG. 2 is a block diagram of a noise removal device showing a second embodiment of the present invention. This embodiment uses the conventional noise removal circuit 10 as the input of the first embodiment shown in FIG.
, and the configuration of each is the same.

[0021] In a laser disc player, the audio signal is FM modulated and recorded on the disc while being superimposed on the FM modulated video signal, so that interference due to cross modulation appears in the reproduced signal. Specifically, this interference is approximately 2.5M
It has a frequency of Hz. Therefore, first, the noise removal circuit 1
0 removes this interference. Next, noise in the color signal band is removed using the same circuit as in the first invention, which is connected later. According to this configuration, it is possible to effectively remove both interference caused by cross-modulation and noise caused by other causes, so that a large effect of improving image quality can be obtained.

[0022]

As described above, the present invention combines the YC separation circuit 2 using a comb filter and the noise removal circuit 3 used for outputting the luminance signal, thereby improving the S/N of the color signal. can.

[0023] Furthermore, the present invention provides another input to the first invention.
By providing two noise removal circuits 10, both cross-modulation removal and S/N improvement can be effectively performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a noise removal device in a first embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a noise removal device in a second embodiment of the present invention.

FIG. 3 is a characteristic diagram showing two-dimensional frequency characteristics of a video signal in an embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a conventional noise removal device.

[Explanation of symbols]

2 YC separation circuit 3,10 Noise removal circuit 4,11 Bandpass filter 5, 12 Limiter 6,13 Subtractor

Claims (5)

[Claims] 1. A YC separation circuit using a comb filter that separates an input video signal into a carrier color signal and a luminance signal; A noise removal circuit that removes noise;
A noise removal device comprising: an addition circuit that adds the carrier color signal output obtained by separation by the YC separation circuit and the output of the noise removal circuit. 2. The noise removal circuit includes a bandpass filter that extracts a signal in the carrier color signal band of the input signal, a limiter circuit that allows the signal to pass only when its output is small, and subtracts the output of the limiter circuit from the input signal. 2. The noise removal device according to claim 1, further comprising a subtracter. 3. A first noise removal circuit that removes noise in a specific band of an input video signal, and a YC separation circuit using a comb filter that separates the output into a carrier color signal and a luminance signal. a second noise removal circuit that removes noise in the carrier color signal band of the luminance signal separated by the YC separation circuit, and a carrier color signal output obtained by separation by the YC separation circuit and the second noise removal circuit; A noise removal device comprising: an addition circuit that adds the outputs of the noise removal circuits; 4. The first noise removal circuit includes a first bandpass filter that extracts a signal in a specific band of the input signal, a first limiter circuit that allows the signal to pass only when the output thereof is small, and a first limiter circuit that extracts a signal in a specific band from the input signal. 4. The noise removal device according to claim 3, further comprising a first subtracter that subtracts the output of the first limiter circuit. 5. The second noise removal circuit includes a second bandpass filter that extracts a signal in the carrier color signal band of the input signal, a second limiter circuit that allows the signal to pass through only when the output thereof is small, and a second limiter circuit that extracts the signal in the carrier color signal band of the input signal. and a second subtracter for subtracting the output of the second limiter circuit from the second limiter circuit.
The noise removal device described.