JPS6330085A - Luminance signal and chrominance signal separating circuit - Google Patents

Abstract

PURPOSE:To reduce cross color disturbance by detecting the vertical and horizontal correlativity of a picture and limiting a horizontal frequency band of a signal separated as a chrominance signal narrowly with respect to a picture (white/black level slant lines) weak in both the vertical/horizontal correlativity. CONSTITUTION:The vertical correlativity of a picture is obtained by using a vertical correlation device 12 from an input signal of a 1H memory 2 and an output signal of a 1H memory 3. The horizontal correlativity of a picture is obtained from an output signal of the 1H memory 2 by using a horizontal correlation device 13. The signal from the vertical correlation device 12 and the horizontal correlation device 13 is inputted to a decoder 14, weighting circuits 15, 16 are controlled by using a control signal to change the mixture ratio of an output CW of a broad band filter 8a and an output CN of a narrow band filter 8b. That is, a chrominance signal C=KCW+(1-K)CN is obtained from the mixer 17. When no correlativity exists. in both vertical/horizontal directions, the value K is selected as 0, the band of the chrominance signal is narrowed to reduce the cross color disturbance. If either the vertical or the horizontal direction has correlatibity, the value K is selected as 1.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a color television receiver, and in particular to a luminance signal that accurately separates a luminance signal (Y) and a color signal (C) from a composite video signal. - This relates to a color signal separation circuit (hereinafter referred to as a Y/C separation circuit).

[Conventional technology]

Conventionally, in an NTSC color television signal, in order to compress the band, the color signal (C) is interpolated and multiplexed into the gap between the spectra in the high frequency part of the luminance signal (Y) using the principle of frequency interleaving. There is. For this reason, it is necessary for the receiver to perform Y/C separation on the received color television signal, and methods for doing so include a Y/C separation method using a low-pass filter and a band-pass filter, and a comb-shaped filter using a scanning line memory. Method (Television Society Journal Vol.
1.151a4 (+979) P27i to 276 "Digital processing technology in television 2 - Synthesis and separation of color television signals").

In the case of the former method, in order to obtain a luminance signal from which color signals have been sufficiently removed, it is necessary to widen the passband width of the bandpass filter, which results in the loss of high-frequency components of the luminance signal, resulting in degraded resolution. There was a drawback.

FIG. 5 is a block diagram showing the latter method, that is, a conventional Y/C separation circuit using a comb filter.

In the figure, 1 is a composite video signal input terminal, 2 and 3 are each a 1H delay line, 4 to 6 are each a multiplier, 7 is an adder, 8 is a band pass filter, 9 is a subtracter, and 10 is a color signal output Terminal 11 is a luminance signal output terminal.

In this Y/G separation circuit using a comb filter, the displayed images are basically correlated in the vertical direction, and N
In the TSC method, the Y/C
It performs separation.

FIG. 6 is a waveform diagram showing signal waveforms at various parts of the circuit of FIG.

The circuit operation will be explained with reference to FIGS. 5 and 6.

When the (t+1)th line signal of the composite video signal input from terminal 1 is on the output side of 1H delay line 3, the tth line signal is on the output side of 1H delay line 2 (input side of 1H delay line 3). ), and the signal on the (t-1)th line is on the input side of the 1H delay line 2.

Figure 6 (A) shows the signal waveform of each line (carrier color signal frequency-multiplexed with the luminance signal, in other words, the waveform of the video signal itself, but the color signal part is emphasized for easy understanding). This is an indication.) is an indication. As shown in this figure, the phase of the color subcarrier is inverted for each line.

Next, in (B) of FIG. 6, the signal of each line is input to the multiplier 4.
6 shows waveforms obtained by weighting 1/4.1/2 and -1/4 times, respectively (the negative sign when weighting means phase inversion).

Next, the outputs of these multipliers 4 to 6 are added by an adder 7, and then passed through a bandpass filter 8 to extract the frequency (=!, 58MHz) of the color subcarrier, thereby converting the (t) line. The color signal in the eye video signal can be extracted as shown in FIG. 6(C). On the other hand, the subtracter 9 is a circuit that subtracts the extracted color signal component from the (t)th line video signal, and as a result, the output (
Second, as shown in FIG. 6(D), only the luminance signal can be obtained.

Figure 7 shows the two-dimensional frequency characteristics of the color signal and luminance signal in the Y/C separation circuit shown in Figure 5 (-). In the figure, the horizontal axis (μ) is the frequency in the horizontal direction of the image,
Represents the number of times the video signal is repeated in the horizontal direction of the image.

The vertical axis (ν) is the vertical frequency of the image, whose units [:
zph] represents the number of times the video signal is repeated in the vertical direction of the screen.

In the color signal, the color subcarrier has a horizontal frequency f 5 (-i58
M H2% Since the vertical frequency is located at 525/4 tPh (indicating that the phase of the color subcarrier is inverted for each line), it is distributed in the vicinity thereof. Therefore, the shaded area in the figure is extracted as a color signal using the band-pass filter 8 and the comb filter described above. Furthermore, since the luminance signal is obtained by sensing the color signal extracted from the video signal, the frequency region is the entire frequency region excluding the region extracted as the color signal.

[Problem that the invention seeks to solve]

The above conventional technology has no problem if the luminance signal does not have components in the frequency domain (the shaded area in Figure 7) that are extracted as color signals, but if it does have those frequency components, it is not used as a color signal. There was a problem in that the image was extracted and so-called cross-color interference occurred.

This will be explained using FIG. 8. FIG. 8 shows the frequency distribution of the luminance signal depending on the state of each image (the part surrounded by a solid line), and the frequency region separated as a color signal by the comb filter and the bandpass filter (the shaded part).

FIG. 8A shows an image that is flat in the vertical and horizontal directions, that is, an image that has low vertical and horizontal frequencies.

In this case, both the vertical correlation and the horizontal correlation of the images are strong. The luminance signal at this time has frequency components in the area surrounded by a solid line in the figure, and does not have frequency components in the area (shaded area) that is separated as a color signal. Therefore, in this case, no cross color interference occurs.

FIG. 8B shows an image in which black and white are repeated in the vertical direction, that is, an image in which the vertical frequency is high and the horizontal frequency is low. In this case, the vertical correlation of the images is weak and the horizontal correlation is strong. The luminance signal at this time has frequency components in the area surrounded by a solid line in the figure, and does not have frequency components in the area that is separated as a color signal. Therefore, in this case as well, cross color interference does not occur.

FIG. 8C shows an image that repeats black and white in the diagonal direction, that is, an image that has both high vertical and horizontal frequencies. In this case, both the vertical and horizontal correlations of the IjiJ image are weak. The luminance signal at this time has frequency components that are separated as color signals, as shown in the figure. Therefore, in this case, cross color interference occurs.

The eighth diagram represents an image that repeats black and white in the horizontal direction, that is, an image that has a low vertical frequency and a high horizontal frequency. In this case, the images have strong vertical correlation and weak horizontal correlation. As shown in the figure, the luminance signal at this time does not have a frequency component in a region that is separated as a color signal. Therefore, in this case, no cross color interference occurs.

As mentioned above, the conventional Y/
In the C separation circuit, for images such as black and white diagonal lines, that is, images with high vertical and horizontal frequencies (images with weak vertical and horizontal correlations), the luminance signal is separated as a color signal, so the cross-color There was a problem that interference occurred.

The purpose of the present invention is to solve the above-mentioned problems of the prior art,
It is an object of the present invention to provide a Y/C separation circuit capable of reducing cross color interference occurring in images such as white and black diagonal lines, that is, images having high vertical and horizontal frequencies.

[Means for solving problems]

In order to achieve the above object, the present invention provides means for detecting the correlation in the vertical and horizontal directions of images, and for images with weak vertical and horizontal correlations (white and black diagonal lines), the color By narrowly limiting the horizontal frequency band of the signals that are separated, cross-color interference is reduced.

[Effect]

FIG. 9 is an explanatory diagram for explaining the outline of the operation of the present invention, and shows the frequency domain of a signal extracted as a color signal.

In the present invention, if the image has a strong correlation in either the vertical or horizontal direction (the luminance signal does not have frequency components in the shaded area in the figure), a broadband filter is used to filter the area surrounded by the solid line in the figure. is extracted as a color signal. In addition, if the image has no correlation in both the vertical and horizontal directions (the luminance signal has a frequency component in the diagonal part III in the figure), use a narrow band filter to filter the area surrounded by the dotted line in the figure to the chrominance signal. This reduces the mixing of the luminance signal into the color signal component and reduces cross-color interference.

That is, in the present invention, images with weak vertical and horizontal correlations, such as black and white diagonal lines, are determined by the above-described means for determining vertical correlation and horizontal correlation of images, and for such images, Cross-color interference is reduced by limiting the band of signals separated as color signals to a narrow band.

〔Example〕

Hereinafter, a first embodiment of the present invention will be explained with reference to FIG. 6.
FIG. 1 is a block diagram showing a Y/C separation circuit as a first embodiment of the present invention.

In the figure, 1 is a composite video signal input terminal, 2 and 3
is a 1H mesori (line memory) as a 1H delay means.
, 4 to 6 are multipliers, 7 is an adder, 8a is a wide band pass filter, 8b is a narrow band pass filter, 9 is a subtracter, 10 is a color signal output terminal, 11 is a luminance signal output terminal, 12 is a stationary correlator , 13 is a horizontal correlator, 14 is a decoder, 15 and 16 are weighting circuits, and 17 is a mixer (adder).

The Y/C separation circuit according to the present invention shown in FIG. 1 has a vertical correlator 12 and a horizontal correlator 13 newly added to the conventional Y/C separation circuit shown in FIG. 8, a wide band pass filter 8a, a narrow band pass filter 8b1, and weighted circuits 15, 16, and a mixer 17 are provided.

Note that the pass band of the wide band pass filter 8a is the same as that of the band pass filter 8.

The basic operation of this Y/C separation circuit is as follows.

1) Using the input signal of the 1H memory 2 and the output signal of the 1H memory 6, use the vertical correlator 12 to find the correlation in the vertical direction of the image.

2] Find the correlation in the horizontal direction of the image using the horizontal correlator 13 from the anal force signal of the 1H memory 2 (input signal of the IH memory 3).

3) The signals from the vertical correlator 12 and the horizontal correlator 13 are decoded by the decoder 14, and the weighting is performed by controlling the circuits 15 and 16 using the decoder 14 and applying the weighting to the wideband filter 8.
The mixing ratio between the output of the filter a and the output of the narrowband filter 8b is changed. In other words, from the mixer 17, the color signal C-KCw+(1-
K) ON (however, CW is the output of the wideband filter 8a, C
N is the output of the narrow band filter 8b] is obtained.

4) If there is no correlation in both the vertical and horizontal directions, set K→0 and make the color signal band narrow as shown in FIG. 9 to reduce cross color interference.

5) If there is correlation in either the vertical or horizontal direction, -1
The operation is similar to that of the Y/C separation circuit shown in FIG.

Next, detection of correlation in the vertical and horizontal directions in the vertical correlator 12 and horizontal correlator 13 of FIG. 1 will be explained using FIG. 2 and FIG. 5.

Figure 2A shows 1H when there is correlation both vertically and horizontally.
Three scanning line signals (t-1) obtained from memories 2 and 5
, (z), (t+1) lines, and white circles represent sample points (sampling frequency 2fsc
(fsc is the frequency of the color subcarrier). Now, the correlation of the images at the sample point S5 of the (t)th line is determined. If the image has vertical correlation, the color subcarriers at sample points S2 and 88 will be in phase, so the scanning line signals at S2 and 88(-) will be almost equal.Also, if the image has horizontal correlation, the color subcarriers at sample points S2 and 88 will be in phase. Since the color subcarriers at S4 and 86 are in phase, the scan line signals at S4 and 88 are approximately equal.

Figure 2B shows the case where there is no correlation in both the vertical and horizontal directions.
At this time, the color subcarriers at sample points S2, S8 and S4, S6 are not in phase, and the luminance signals also show different values.

Therefore, utilizing the above, the vertical correlator 12 and the horizontal correlator 13 operate as described below.

FIG. 3A is a block diagram showing a specific example of the vertical correlator 12 in FIG. 1. In the figure, 18 is a subtracter, 19 is an absolute value conversion circuit, 20 is a comparator, and 21 is a reference signal input terminal.

That is, the vertical correlator 12 utilizes the fact that if there is vertical correlation in the image, the phase of the color subcarrier two lines before is the same, and the input signal of the 1H memory 2 (line t-1) is
The subtracter 18 calculates the difference between the output signal (line t+1) of the 1H memory 3 and the output signal (line t+1), and the absolute value conversion circuit 19 calculates the absolute value of the difference between the two signals. Furthermore, the absolute value conversion circuit 1
9 and a certain reference signal are compared by a comparator 20, and the correlation in the vertical direction is determined based on the magnitude relationship.

That is, if the output of the absolute value conversion circuit 19 is less than or equal to a certain reference signal, it is determined that there is a correlation, and if it is greater than that, it is determined that there is no correlation.

FIG. 3B is a block diagram showing a specific example of the horizontal correlator 13 in FIG. 1. In the same figure, 22 and 23
is a 1f timing delay element (chimbling frequency is 2fSC)
It is. However, fSC: frequency of color subcarrier (=3.5
8MHz)), 24 is a subtracter, 25 is an absolute value conversion circuit, 2
6 is a comparator, and 27 is a reference signal input terminal.

The horizontal correlator 13 uses the fact that the phases of the color subcarriers before two samplings in one line (when the sampling frequency is 2fSC) are in phase, and the output signal Ct) of the 1H memory 2 in the 2nd line. The sample-delayed signals are determined by one-sample delay elements 22 and 23, and the difference between them is determined by the subtracter 24. Further, the absolute value of the difference between both signals is determined by the absolute value converting circuit 25, and further, the output of the absolute value converting circuit 25 and a certain reference signal are compared by the comparator 26, and the correlation in the horizontal direction is determined based on the magnitude relationship. Determine. That is, if the output of the absolute value converting circuit 25 is less than a certain reference signal, it is determined that there is a correlation, and if it is more than that, it is determined that there is no correlation.

Furthermore, when sampling is performed using 'fsc', horizontal correlation may be determined using data between 4f pairs.

Next, a second embodiment of the present invention will be described using FIG. 4.

The difference between the embodiment shown in FIG. 4 and the embodiment shown in FIG. It is a point. Note that 61 is a reference signal input terminal.

That is, the detection of image correlation in this embodiment is carried out by passing a signal with a high vertical frequency obtained from the adder 7 through a comb filter to a low-pass filter 28. By determining a signal with a low frequency, then determining the absolute value of the output of the low-pass filter 28 using an absolute value converting circuit 29, and then comparing a certain reference signal and the output of the absolute value converting circuit 29 in a comparing circuit 30. conduct.

In other words, when the output of the absolute value conversion circuit 29 is larger than a certain reference signal, it indicates a signal with a high vertical frequency and a low horizontal frequency (such as black and white horizontal stripes), and in this case, there is no vertical correlation and no horizontal correlation. It is determined that there is. Further, if the output of the absolute value converting circuit 29 is smaller than a certain reference value, it indicates a signal with high vertical and horizontal frequencies (such as black and white diagonal stripes), and in this case, it is determined that there is no vertical or horizontal correlation.

If it is determined that there is no vertical or horizontal correlation, the weighting is changed from K to 0 by circuits 15 and 16, and the band of the color signal is narrowed to reduce cross color interference.

Note that the bandpass filter 8a shown in FIG. 1 or 4,
8b, if the I and Q signals are considered, the bandwidths may be approximately ±1.5 MHz and ±0.5 MHz, respectively, but if the R-Y and B-Y signals are considered, the bandpass filters 8a, The band 8b may be further narrowed.

〔Effect of the invention〕

As described above, according to the present invention, cross-color disturbances in images such as black and white diagonal stripes that have conventionally occurred are determined by determining the correlation in the vertical and horizontal directions of the image, and if there is no correlation in both directions, the cross-color interference This can be reduced by making the signal narrowband so that it can be separated as a signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is an explanatory diagram for explaining image correlation, and FIG. 3 is a vertical correlator and horizontal correlator in FIG. 1. 4 is a block diagram showing a second embodiment of the present invention, FIG. 5 is a block diagram showing a conventional Y/C separation circuit, and FIG. 6 is a block diagram showing a conventional Y/C separation circuit. 5 is a waveform diagram showing the operating waveforms of each part signal, FIG. 7 is an explanatory diagram showing the frequency domain of the signal separated as a color signal by the Y/C separation circuit of FIG. 5, and FIG. FIG. 9 is an explanatory diagram showing the frequency distribution of the luminance signal depending on the state, and is an explanatory diagram for explaining the outline of the operation of the present invention. Explanation of symbols 1... Composite video signal input terminal, 2, 6... 1H memory, 4 to 6... Multiplier, 7... Adder, 8a...
Broadband filter, 8b... Narrowband filter, 9...
Subtractor, 10... Color signal output terminal, 11... Luminance signal output terminal, 12... Vertical correlator, 13... Horizontal correlator, 14... Decoder, 15.16... Weight Attached is the circuit, 17...Mixer agent, patent attorney Katsuo Ogawa, 1st figure 8.
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Claims (1)

[Claims] 1. Input a composite video signal in which a luminance signal and a chrominance signal are frequency multiplexed, input a comb filter that limits the vertical frequency band of the signal, and input the output signal from the comb filter. A luminance signal/chrominance signal separation circuit for separating the luminance signal and the chrominance signal from the composite video signal, the circuit comprising at least a bandpass filter for extracting the color signal by limiting a horizontal frequency band; Correlation detection means for detecting correlation in the vertical and horizontal directions of images in the image is provided, and a variable bandpass filter whose pass band changes according to the detection result by the correlation detection means is provided in place of the bandpass filter. established,
A luminance signal/chrominance signal separation circuit characterized in that, for an image having weak correlations in both the vertical and horizontal directions, the horizontal frequency bandwidth of the extracted color signal is narrowed to a predetermined value or less.