JPH02141192A - Luminance chrominance signal separation filter corresponding to picture correlation - Google Patents

Abstract

PURPOSE:To prevent the picture quality deterioration of a reproduced picture such as dot disturbance by applying weighting to each direction chrominance signal extraction filter output in response to the result of picture correlation detection whose isolation point is eliminated in the vertical and horizontal directions and summing each filter output and outputting the result as a color signal component. CONSTITUTION:The correlation of a picture is detected by a picture correlation detection circuit 7. An isolation point elimination circuit 14 compares a noted sample point and two reference sample points and when the reference sample point is larger, the value of the noted sample point is replaced into the value close to the noted sample point in the two reference sample point outputted. Then an output 135 passes through one sample delay circuits 5k, 5l and since the 3 sample points whose isolating point are eliminated in the vertical direction arranged in the horizontal direction on the pattern is obtained and the isolation point in the horizontal direction is eliminated in addition to the value in the vertical direction. A mixing circuit 8 applies weighting to each filter output in response to the result of correlation of the picture, mixes it and the result is sent as the color signal component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a luminance signal color signal separation filter compatible with image correlation, and particularly to a luminance signal color signal separation filter for separating luminance signals and color signals from a composite television signal of the NTSC system, for example. Related to signal separation filters.

[Conventional technology]

FIG. 4 is a block diagram showing an example of the configuration of a conventional luminance signal chrominance signal separation filter. In the figure, an NTSC composite color television signal is input to an input terminal 1. The composite color television signal is applied to a vertical filter 6j via an A/D converter 4, and
It is applied to the line delay circuit 5m. 1 line delay circuit 5
The output of m is applied as it is to the vertical filter 6j, and after being further delayed by one line in the one line delay circuit 5n, it is applied to the vertical filter 6j. The vertical filter 6j is a filter usually called a two-line comb filter, and its output is sent to the bandpass filter 6.
given to k. The output to the bandpass filter 6 is the color signal 20
5 from the output terminal 2 and is applied to the first input of the subtraction circuit 9C. Further, the output of the l-line delay circuit 5m is applied to the second input of the subtraction circuit 9C via the compensation delay circuit 50. The compensation delay circuit 50 is a circuit for compensating for the delay in the bandpass filter 6k. A luminance signal 207 is output from the subtraction circuit 9C and applied to the output terminal 3.

Next, the operation of the filter for an NTSC composite color television signal will be explained.

The composite color television signal 201 sampled in synchronization with the color subcarrier at the sampling frequency fs = 4·fsc (fsc is the color subcarrier frequency) is displayed on the screen as a two-dimensional grid-like array as shown in FIG. Become. That is, f sc = (45
5/2) f o, the phase of the color signal C is inverted by 180'' for each line, and 4 samples are extracted in one cycle.Here, in the figure, Y is the luminance signal, C,...
C, indicates a color signal. Now, it is assumed that Z-1 and Z-L are used as symbols to represent the delay of one sample and the delay of one line, respectively, using Z transformation. Here, Z-'=exp (-J2ycf/4f sc). Furthermore, since f sc = (455/2) f H, ff1=910. At this time, the delay circuit 5
From the 1-line delayed signal 202 and 2-line delayed signal 203 and the current input signal 201 delayed using i and 5j, the vertical filter 6j extracts a line support signal 204 that supports each line including the color signal. do. The transfer function Hv (Z) of the vertical filter 6j is Hv (Z) = (-1/4) (1-Z-')
”.In other words, the line support signal Hc (m, n) at the coordinates (m, n) on the screen in FIG.
1/4) (S(m,n-1)-2S(o+,n)
+S (m, n+1) will be extracted as 1.

Since the line support signal also includes the luminance signal Y, the bandpass filter 6k converts the color signal C(m, n), which is a high frequency component, into Hc(rn).

n). And the color signal 2 obtained by this
05 is sent to the subtraction circuit 9c. The subtraction circuit 9c generates a signal S (m, n) 206 obtained by further delaying the one-line delayed signal 202 by the compensation delay circuit 5o according to the bandpass filter 6k.
The color signal C(m,n) 205 is subtracted from the luminance signal Y(m.

n) Separate 207.

Y (m, n) = S (m, n>-C (m, n) The transfer function Hh (Z) to the bandpass filter 6 is, for example, Hh (Z) = (-1/32) (1- Z −”ν(1+Z
-')"(1+Z-").

[Problem to be solved by the invention]

The conventional luminance signal/chrominance signal separation filter is configured by fixing the characteristics of the vertical filter and the horizontal filter and combining them as described above. That is, the luminance signal and the color signal are separated by bandpass filters in both the vertical and horizontal directions. Therefore, in the conventional method described above, in areas where the brightness and color of the image change rapidly, the brightness signal and the color signal leak into each channel, which causes problems such as deterioration of the quality of the reproduced image, especially due to dot interference. There was a point.

This invention was made in order to solve the problems of the conventional ones as described above, and it provides a luminance signal and chrominance signal that can achieve accurate separation of the luminance signal and chrominance signal even in sudden signal changes in a television image. The purpose is to provide a separation filter.

[Means to solve the problem]

The image correlation compatible luminance signal/chrominance signal separation filter according to the present invention includes a delay means for simultaneously obtaining a sample point of interest and a sample point close to the sample point from which the two luminance signal signals are to be separated by delaying the input sampling signal; An image correlation detection means for detecting image correlation from the values of the sample point of interest and neighboring sample points is provided, and the outputs of the horizontal filter, vertical filter, and horizontal/vertical filter are weighted according to the detection results. The mixed value is used as the color signal output of the luminance signal color signal separation filter, and furthermore, isolated points are removed from the image correlation detection results.

[Effect]

In this invention, the luminance signal and chrominance signal separation filter is adaptively changed based on the correlation between the vertical and horizontal images of the composite video signal, so that the luminance signal and chrominance signal are separated from each other in areas where the image changes rapidly. The effect of leakage can be reduced, and dot interference can be reduced.

Furthermore, since isolated points are removed from the image correlation detection results, a natural image can be obtained even at the edge portions of the image.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram showing one embodiment of the present invention. In the figure, reference numeral 1 denotes an input terminal to which an NTSC composite color television signal is applied, and this composite color television signal is applied to an A/D converter 4. 4 is an A/D converter configured to sample the composite color television signal at a sampling frequency fs=4fsc. The composite color television signal sampled by this A/D converter 4 is given to an 1-line delay circuit 5a, and further passes through a 1-line delay circuit 5b to determine the sample value at a certain sampling point and the Sample values at sample points one line above and l lines below the sample point on the screen are simultaneously extracted.

The sample values extracted by the l-line delay circuits 5a and 5b are applied to the vertical color signal extraction filter 5a.

The following information is applied to the horizontal color signal extraction filter 6b, the horizontal/vertical color signal extraction filter 6c, and the image correlation detection circuit 7.

That is, the output 101.1 of the A/D converter 4, the output 102.1 of the line delay circuit 5a are input to the vertical color signal extraction filter 5a, the horizontal/vertical color signal extraction filter 5c, and the image correlation detection circuit 7. and the output 103 of the one-line delay circuit 5b.

Further, the output 102 of the one-line delay circuit 5a is applied to the horizontal color signal extraction filter 6b. At this time, for example, when the vertical color signal extraction filter 6a is expressed using a transfer function, it is expressed as "Cv (Z) = (-1/4) (1-Z-L)", and the horizontal color signal The extraction filter 6b is expressed as Ch(Z)-(-1/4) (1-Z-'')'', and the horizontal/vertical color signal extraction filter 6C is expressed as Chv(Z)=(-1/ 4) (1-Z””)” ・(
-1/4)(1-Z-')2.

The output 104 of the vertical color signal extraction filter 6a is passed through the compensation delay circuit 5c to the horizontal color signal extraction filter 6b.
The output 106 of the horizontal/vertical color signal extraction filter 6C is supplied to the mixing circuit 8 via the compensation delay circuit 5d, and the output 108 of the horizontal/vertical color signal extraction filter 6C is supplied to the mixing circuit 8 via the compensation delay circuit 5e. Further, after isolated points are removed from the output 130 of the image correlation detection circuit 7 by the isolated point removal circuit 14, it is given as a control signal to the mixing circuit 8 together with the constant generation circuits 12a and 12b. The output 111 of the mixing circuit 8 is output as a color signal from the output terminal 2, and is also output from the subtraction circuit 9.
is given to one input of a.

The output 102 of the one-line delay circuit 5a is applied to the other input of the subtraction circuit 9a via the compensation delay circuit 5f. The output 113 of the subtraction circuit 9a is outputted from the output terminal 3 as a luminance signal. Note that the compensation delay circuits 5c, 5d,
5e and 5f are circuits for compensating for delays in each circuit.

FIG. 2 shows an example of the configuration of the image correlation detection circuit 7.

An output 101 of the A/D converter 4, an output 102 of the line delay circuit 5a, and an output 103 of the line delay circuit 5b are applied to a vertical low-pass filter 6g and vertical band-pass filters 6f and 6d.

Further, the output 102 of the one-line delay circuit 5a is given to the horizontal band-pass filter 61. The output 114 of the vertical band-pass filter 6d is applied to one input of the adder circuit 13a via the horizontal low-pass filter 6e and the absolute value circuit 10a.

On the other hand, the output 117 of the vertical band-pass filter 6f is given to the absolute value circuit 10b via the compensation delay circuit 5g. The compensation delay circuit 5g is a circuit for compensating for the delay in the horizontal low-pass filter 6e. Absolute value circuit 1
The output of 0b is applied to the other input of the adder circuit 13a via the multiplier circuit 11a.

The output 121 of the vertical low-pass filter 6g is applied to one input of the adder circuit 13b via the horizontal band-pass filter 6h and the absolute value circuit 10c. On the other hand, the output 124 of the horizontal band-pass filter 61 is given to the absolute value circuit 10d via the compensation delay circuit 5h. The compensation delay circuit 5h is a circuit for compensating for the delay in the horizontal band-pass filter 6h. The output of the absolute value circuit 10d is applied to the other input of the addition circuit 13b via the multiplication circuit 11b.

At this time, for example, the vertical low-pass filter 6g is expressed as Fvl (Z)=(1/4)(1+Z-L)'', and the horizontal band-pass filter 6h is expressed as Fhh(Z)=
1-Z-', that is, it is expressed as extracting the frequency component corresponding to A of the color subcarrier frequency in the horizontal direction. Further, the horizontal band-pass filter 61 is expressed as Fdh(Z)=1-Z −', and the vertical band-pass filter 6d is expressed as Fvh
(Z)=1−Z −”, that is, it is expressed as extracting the frequency component corresponding to A of the color subcarrier frequency in the vertical direction. Also, the horizontal low-pass filter 6e is Fhl (Z)=(1/4)(1+Z-")", and the vertical band-pass filter 6f is Fdv(Z)
This is a digital filter that can be expressed as "Electronic 1-Z-".

Outputs 128 and 129 of the adder circuits 13a and 13b are given to the subtracter circuit 9b, and an output 110 of the subtracter circuit 9b is sent out as an image correlation detection result.

FIG. 3 shows an example of the configuration of the isolated point removal circuit 14 shown in FIG. The output 130 of the image correlation detection circuit 7 is sequentially applied to the 1-line delay circuit 5 and 5j, thereby simultaneously obtaining the results of image correlation detection at sample points arranged vertically on the screen. Output 1 of image correlation detection circuit 7
30 is also given to one input of the maximum value selection circuit 15a, the output 132 of the one line delay circuit 5j is given to one input of the maximum value selection circuit 15b, and the output 132 of the one line delay circuit 5j is given to one input of the maximum value selection circuit 15b, and The output 131 of the 1-line delay circuit 51 is applied to the input. The outputs 133 and 134 of the maximum value selection circuits 15a and 15b are given to the minimum value selection circuit 15c.

The output 135 of the minimum value selection circuit 15c is sent as the correlation detection result of the image from which isolated points in the vertical direction have been removed, and is sequentially added to 5N to the 1-sample delay circuit 5. As a result, correlation detection results for images from which isolated points have been removed in the vertical direction from sample points arranged horizontally on the screen can be simultaneously obtained. The output 135 of the minimum value selection circuit 15c is also
The output 137 of the one-sample delay circuit 5β is applied to one input of the minimum value selection circuit 15e, and the output 137 of the one-sample delay circuit 5β is applied to the minimum value selection circuit 15d.
is applied to one input of the minimum value selection circuit 15d,
The output 136 of the 1-sample delay circuit 5 is applied to the other input of t5e. Minimum value selection circuit 1sct, 1s
Outputs 138 and 139 of e are given to the maximum value selection circuit 15f. The output 110 of the maximum value selection circuit 15f is sent as a correlation detection result of an image from which isolated points have been removed not only in the vertical direction but also in the horizontal direction.

Next, the operation will be explained.

The sampling series 101 of the NTSC composite color television signal sampled by the A/D converter 4 at the sampling frequency fs=4fsc is transmitted through delay circuits 5a and 5b, thereby causing the line on the screen to be on the straight line. Sample values at three sample points will be obtained simultaneously. That is, the coordinates (m,
Composite color television signal (sample value) at position n)
S (m.

n) appears on signal line 102, signal line 10
3, a signal 3 (m, n-1) appears on the signal line 101
A signal S (m, n+1) appears at (see FIG. 5).

A luminance signal and chrominance signal filter is constructed based on the sample values of sample points over three lines on the screen.

In this method, the vertical color signal extraction filter 6a.

The horizontal color signal extraction filter 6b and the horizontal/vertical color signal extraction filter 6C extract color signals through filter processing having the following transfer function.

Vertical color signal extraction filter Cv(Z)=(-1/4)(1-Z-L)"Horizontal color signal extraction filter Ch(Z)=(-1/4)(1-Z-")" Horizontal/
Vertical direction color signal extraction filter Chv (Z) J-1/4) (1-Z -")" ・(-
1/4)(1-Z-L)t Vertical filter output 104 and horizontal filter output 106 obtained in this way
．． The horizontal and vertical color signal extraction filter outputs 108 are respectively sent to the mixing circuit 8 via compensation delay circuits.

Here, the vertical color signal extraction filter 6a.

The operation of the mixing circuit that mixes the color output signals of the horizontal color signal extraction filter 6b and the horizontal/vertical color signal extraction filter 6C will be described.

The mixing circuit 8 detects the correlation between images in the vertical direction and the horizontal direction regarding the sample point of interest, and selects the vertical color signal extraction filter 6a depending on how strong the correlation is in either the vertical direction or the horizontal direction. , the output of the horizontal color signal extraction filter 6b, and the output of the horizontal/vertical color signal extraction filter 6C are weighted and mixed, respectively.

Detection of image correlation is performed by the image correlation detection circuit 7 as follows.

Let the vertical direction uncorrelated energy be l)v (Z) and the horizontal direction uncorrelated energy be Dh (Z), introduce an absolute value approximation, and express it as follows using a transfer function.

Dv (Z) = l 1-Z-'' Dh (Z) = 11-Z-' The above two equations have filter characteristics that block DC components and color subcarrier frequency components in the vertical and horizontal directions. In addition, the horizontal high-frequency luminance signal energy is DYh
(Z), the vertical high-frequency luminance signal energy is DYV (Z
), introduce the absolute value neighborhood, and use the transfer function to express it as follows.

DYh(Z)=l(1/4)(1+Z-')"
・(1-Z-')DYv(Z)=l (1/4)
(1+Z-")"/(1-Z-") At this time, the image correlation X I (Z) is obtained as follows.

X I(Z) ・(DYv(Z)+Dv(Z))−(
DYh (Z)+0h (Z)) Therefore, the above x I
(Z) takes a negative value when the correlation is strong in the vertical direction, and takes a positive value when the correlation is strong in the horizontal direction.

The isolated point removal circuit 14 detects the correlation detection results X, (Z
), the isolated points are removed as follows.

That is, in the circuit shown in FIG. 3, the detection results of image correlation at three sample points arranged vertically on the screen are obtained at each input/output of the delay circuit 51.degree. 5j. The center sample point is the target sample point, and the two sample points above and below it are the reference sample points.

Here, when comparing the sample point of interest and the two reference sample points, if both reference sample points are large, the value of the sample point of interest will be the one of the two reference sample points that is closer to the value of the sample point of interest. Replaced and output. In addition, in cases other than the above, the value of the sample point of interest is output as is. Therefore, the correlation detection result from which isolated points have been removed in the vertical direction appears at the output 135 of the minimum value selection circuit 15c.

Next, the output 135 is a one sample delay circuit 5k.

5β, and three sample points lined up horizontally on the screen from which isolated points are removed in the vertical direction are obtained, so we can use the same argument as before (however, the polarity of the vertical and horizontal correlation results is opposite). Therefore, by reversing the magnitude relationship during comparison), isolated points are removed not only in the vertical direction but also in the horizontal direction. Therefore, vertically,
The correlation result of the image from which isolated points have been removed in both the horizontal direction
Z) is obtained from the isolated point removal circuit 14.

The mixing circuit 8 outputs Cv according to the correlation result of the image.
(Z), Ch (Z), and Chv (Z) are weighted and mixed and sent out as a color signal component.

The color signal extraction filter characteristic C(Z) is expressed as the following equation.

C (Z) = αCv (Z) + βCh (Z) + r C
hv (Z) where α, β, and γ are respectively Cv (Z),
Mixing ratio of Ch(Z) and Chv(Z), 0≦α, β.

γ≦1. α+β+r=1, and the correlation detection result is X! (Z
) have the following characteristics.

Xt(Z)≦kl (kl <O: correlation constant)
When α-1, β-γ=O, when k1≦Xz(Z)≦O, α-(1/to)・X, (Z).

β-〇.

r= (+ to 1/) ・Xt(Z) + 10≦
X! (Z) When 6 kg (k, > Q: correlation threshold constant), α-〇.

β=　(1/　kg　　)　・Xz(Z).

γ= (1/kg) ・X! (Z) + 1X
When t (Z)≧, α=γ−0, β=1 Note that the correlation threshold constants , kt are provided by the constant generation circuits 12a and 12b, respectively.

The color signal output of the mixing circuit 8 is subtracted from the composite video signal of the output 112 of the compensation delay circuit 5f, and the luminance signal 11
3 is required.

As described above, according to the present embodiment, the correlation of the image is detected from the values of the sample point of interest and the neighboring sample points, and the output of the horizontal filter, vertical filter, and horizontal/vertical filter is determined according to the detection results. The weighted and mixed value is used as the color signal output of the luminance signal color signal separation filter, and isolated points are removed from the image correlation detection results, so the vertical and horizontal directions of the composite video signal are The luminance signal and chrominance signal separation filter can be adaptively changed according to the correlation of the directional images, and the influence of leakage of the luminance signal and the chrominance signal to each other channel in areas where the image changes rapidly can be reduced. It is possible to reduce dot interference, and moreover, it is possible to naturally reproduce areas with rapid changes in the image.

In the above embodiment, the composite color television signal is sampled at a frequency four times as high as the color subcarrier synchronized with the horizontal scanning frequency. For example, sampling is not limited to four times the color subcarrier, but may be performed at other frequencies.

Further, the digital filter used in the above embodiment is merely an example, and the filter may be constructed with a higher order, for example.

〔Effect of the invention〕

As described above, according to the image correlation compatible luminance signal chrominance signal separation filter according to the present invention, the luminance signal chrominance signal separation filter can be adaptively divided by the image correlation between the vertical direction and the horizontal direction of the composite color television signal. By changing the dots and removing isolated points from the image correlation detection results, it is possible to reduce the leakage of the luminance signal and color signal into each other's channels, reduce dot interference, and improve the image quality. This has the effect of being able to reproduce areas with rapid changes naturally.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an NTSC system image correlation compatible luminance signal/chrominance signal separation filter according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the configuration of the image correlation detection circuit, and FIG. is a block diagram showing an example of the configuration of an isolated point removal circuit, FIG. 4 is a schematic block diagram showing an example of the configuration of a conventional luminance signal/chrominance signal separation filter, and FIG. FIG. 2 is an explanatory diagram showing an arrangement on a screen of a signal sequence synchronously sampled at four times the carrier wave. In the figure, 1 is the input terminal, 2.3 is the output terminal, and 4 is the A
/D converter, 5a to 5 are delay circuits, 6a to 6 are digital filters, 7 is an image correlation detection circuit, 8 is a mixing circuit, 9a to 9C are subtraction circuits, 10a to 10d are absolute value circuits, 12a, 12b is a constant generation circuit, 13a, 1
3b is an addition circuit, 14 is an isolated point removal circuit, 153 to 15
f is a selection circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) Input a composite video signal sampled at a predetermined frequency synchronized with the horizontal scanning frequency so that each sampling point is arranged in a grid on the screen, and digitally calculate the luminance signal component and color from the composite video signal. An image correlation compatible luminance signal/chrominance signal separation filter for separating signal components, the composite video signal being delayed, and a sample point of interest at which the luminance signal and the color signal should be separated, and a sample point perpendicular to the sample point of interest on the screen. delay means for simultaneously obtaining sample values of a plurality of reference sample points arranged in a straight line in the direction; a vertical color signal extraction filter that extracts and outputs a frequency component corresponding to a horizontal color subcarrier component; a horizontal color signal extraction filter; and a horizontal/vertical color signal extraction filter that receives sample values of the sample point of interest and a predetermined reference sample point as input, extracts and outputs frequency components corresponding to color subcarrier components in both the vertical and horizontal directions. a directional color signal extraction filter, which inputs sample values of the sample point of interest and a predetermined reference sample point, and extracts frequency components corresponding to a vertical direct current component and a color subcarrier component from frequency components at the sample point of interest; and a vertical direction uncorrelated energy detection means for detecting vertical direction uncorrelated energy by excluding the absolute value of the vertical direction uncorrelated energy; extracting a frequency component that is a low frequency component in the horizontal direction and corresponds to one half of the color subcarrier frequency in the vertical direction;
vertical high-frequency luminance signal energy detection means for detecting vertical high-frequency luminance signal energy by determining the absolute value thereof; horizontal direction uncorrelated energy detection means for detecting horizontal direction uncorrelated energy by excluding a horizontal direct current component and a frequency component corresponding to a color subcarrier component from among the components and finding the absolute value thereof; The sample value of a sample point and a predetermined reference sample point is input, and the frequency component at the sample point of interest is a low frequency component in the vertical direction, and corresponds to one half of the color subcarrier frequency in the horizontal direction. Extract the frequency components that
horizontal high frequency luminance signal energy detecting means for detecting horizontal high frequency luminance signal energy by determining its absolute value; image correlation detection means for determining image correlation by subtracting a value obtained by adding the horizontal high-frequency luminance signal energy and a value obtained by doubling the horizontal non-correlation energy from the combined value; and the image correlation detection means. By delaying the output of the means for a predetermined period of time, the correlation detection results at multiple sample points aligned vertically on the screen are simultaneously obtained, and the correlation between the sample point of interest and predetermined reference sample points located above and below it is obtained. Compare the size of each,
When it is determined that the sample point of interest is an isolated point, the correlation value of the sample point of interest is replaced with the correlation value of the reference sample point that is closest to the correlation value of the sample point of interest, and the isolated point is determined in the vertical direction. removing the isolated point in the vertical direction, delaying the correlation value of the sample point of interest from which the isolated point has been removed for a predetermined period, and simultaneously obtaining the detection results of the correlation at a plurality of sample points aligned in a straight line in the horizontal direction on the screen; Compare the magnitude of the correlation between the sample point of interest and predetermined reference sample points located on the left and right sides of the sample point, and if it is determined that the sample point of interest is an isolated point, the value of the correlation of the sample point of interest is set to the sample point of interest. isolated point removing means for removing isolated points in the horizontal direction as well as in the vertical direction by replacing the correlation value of the reference sample point closest to the correlation value of the point; After weighting the horizontal color signal extraction filter output, vertical color signal extraction filter output, and horizontal/vertical color signal extraction filter output according to the image correlation detection results, the color signal is obtained by adding up the outputs of each filter. 1. A luminance signal/chrominance signal separation filter for image correlation, comprising: a mixing circuit that outputs the output as a component; and a subtraction circuit that subtracts the output of the mixing circuit from the composite video signal to output a luminance signal component.