JP2529681B2 - Image correlation compatible luminance signal color signal separation filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image correlation-compatible luminance signal color signal separation filter, and more particularly to a luminance signal for separating a luminance signal and a chrominance signal from, for example, an NTSC composite television signal. The present invention relates to a color signal separation filter.

[Conventional technology]

FIG. 5 is a block diagram showing an example of the configuration of a conventional luminance signal / color signal separation filter. In the figure, input terminal 1
Receives a composite color television signal of the NTSC system. The composite color television signal is supplied to the vertical direction filter 6j via the A / D converter 4 and also to the 1-line delay circuit 5i. The output of the 1-line delay circuit 5i is given to the vertical filter 6j as it is, further delayed by 1 line by the 1-line delay circuit 5j, and then given to the vertical filter 6j. The vertical filter 6j is a filter usually called a two-line comb filter, and its output is given to the bandpass filter 6k.
The output of the bandpass filter 6k is derived from the output terminal 2 as a color signal 205 and is provided to a first input of a subtraction circuit 9d. The output of the 1-line delay circuit 5i is given to the second input of the subtraction circuit 9d via the compensation delay circuit 5k.
The compensation delay circuit 5k is a circuit for compensating for the delay in the bandpass filter 6k. The luminance signal is output from the subtraction circuit 9d.
207 is output and given to the output terminal 3.

Next, the operation of the above-described filter for a composite color television signal of the NTSC system will be described.

Sampling frequency fs = 4 · fsc (fsc is the color subcarrier frequency)
The composite color television signal 201 synchronously sampled with the color subcarriers in the above-described manner has a two-dimensional lattice arrangement on the screen as shown in FIG. That is, since fsc = (455/2) f _H , four samples are extracted in one cycle in which the phase shift of the color signal C is inverted by 180 ° for each line. Here, in the figure, Y
Indicates a luminance signal, and C ₁ and C ₂ indicate color signals. Now, as a symbol that represents a delay of one sample and one line delay, and the use of Z ^-1 and Z ^-l using Z transform, respectively. Here, Z ⁻¹ = exp (−j2πf / 4fsc). Further, the l = 910 since it is fsc = (455/2) f _H. At this time, it is delayed by using the delay circuits 5i and 5j.
From the line delay signal 202, the two-line delay signal 203, and the current input signal 201, the vertical direction filter 6j extracts a line support signal 204 that supports each line including the color signal.
The transfer function Hv (Z) of the vertical filter 6j is Hv (Z) = (− 1/4) · (1−Z− ^l ) ² . That is, the line support signal Hc (m, n) at the coordinates (m, n) on the screen of FIG. 6 is converted into Hc (m, n) = (− 1/4) {S (m, n−1) − 2S (m, n) + S
(M, n + 1)} will be extracted. Since the line support signal also includes the luminance signal Y, the bandpass filter 6k separates the color signal C (m, n), which is a high-frequency component, from Hc (m, n). The color signal 205 thus obtained is subtracted by the subtraction circuit 9d.
Sent to The subtraction circuit 9d subtracts the color signal C (m, n) 205 from the signal S (m, n) 206 obtained by delaying the one-line delay signal 202 by the compensation delay circuit 5k according to the bandpass filter 6k,
The luminance signal Y (m, n) 207 is separated as in the following equation.

Y (m, n) = S (m, n) -C (m, n) The transfer function Hh (Z) of the bandpass filter 6k is, for example, Hh (Z) = (-1/32) (1-Z ^-2 ) ² (1 + Z ^-4 ) ² (1
+ Z ^-8 ).

[Problems to be solved by the invention]

The conventional luminance signal color signal separation filter fixes the characteristics of the vertical filter and the horizontal filter as described above,
It was composed in combination. That is, the luminance signal and the chrominance signal are separated by the bandpass filter in both the vertical and horizontal directions. Therefore, in the conventional method, in a region where the luminance and color of the image change greatly, there is a problem that the luminance signal and the chrominance signal leak to the mutual channel, thereby causing deterioration of the image quality of the reproduced image such as dot interference. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a luminance signal color signal separation filter capable of achieving accurate separation of a luminance signal and a chrominance signal even in a sudden signal change in a television image. The purpose is to do.

[Means for solving problems]

The image correlation corresponding luminance signal color signal separation filter according to the present invention includes: a delay unit that delays an input sampling signal to simultaneously obtain a target sample point for separating a luminance signal and a chrominance signal and a sample point close thereto, Image correlation determining means for detecting the image correlation in the vertical direction and the image correlation in the horizontal direction from the values of the sample points of interest and the adjacent sample points, respectively, and determining the correlation of the images. One of the output of the filter, the vertical filter, and the output of the horizontal / vertical filter is used as the color signal output of the luminance signal color signal separation filter.

[Action]

According to the present invention, since the luminance signal and the color signal separation filter are selectively used depending on the correlation between the vertical and horizontal images of the composite video signal, the influence of the leakage of the luminance signal and the chrominance signal to the mutual channel in a region where the image changes drastically. Can be reduced, and dot disturbance can be reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes an input terminal to which a composite color television signal of the NTSC system is supplied, and this composite color television signal is supplied to an A / D converter 4. The A / D converter 4 is configured to sample a composite color television signal at a sampling frequency fs = 4fsc. The composite color television signal sampled by the A / D converter 4 is applied to a one-line delay circuit 5a, and further to a one-line delay circuit 5b.
Through, the sample value at a sample point of interest and the sample values at sample points one line above and one line below the image of the sample sample of interest are simultaneously extracted. The sample values extracted by the 1-line delay circuits 5a, 5a are the vertical color signal extraction filter 6a and the horizontal color signal extraction filter 6
b, the horizontal / vertical color signal extraction filter 6c and the image correlation determination circuit 7 are given as follows.

That is, the input of the vertical color signal extraction filter 6a, the horizontal / vertical color signal extraction filter 6c, and the image correlation determination circuit 7 is the output 101 of the A / D converter 4, the output 102 of the 1-line delay circuit 5a, And the output 103 of the 1-line delay circuit 5b. The output 102 of the one-line delay circuit 5a is provided to the horizontal color signal extraction filter 6b. At this time, for example, the vertical color signal extraction filter 6a is expressed as Cv (Z) = (− 1/4) (1-Z ^−l ) ² when expressed using a transfer function, and the horizontal color signal extraction filter 6a is also expressed. The filter 6b is expressed as Ch (Z) = (− 1/4) (1-Z ⁻² ) ² and also the horizontal / vertical color signal extraction filter 6c.
Is Chv (Z) = (− 1/4) (1-Z ⁻² ) ² · (−1/4) (1-
Z ^−l ) ² is a filter.

The output 104 of the vertical color signal extraction filter 6a is output from the horizontal color signal extraction filter 6b via the compensation delay circuit 5c.
106 is a compensation delay circuit 5d, and the output 108 of the horizontal / vertical direction color signal extraction filter 6c is a compensation delay circuit 5e.
Each is provided to the switch circuit 8. The output 110 of the image correlation determination circuit 7 is supplied to the switch 8 as a control signal. The output 111 of the switch circuit 8 is output from the output terminal 2 as a color signal and is also provided to one input of a subtraction circuit 9a. To the other input of the subtraction circuit 9a, an output 102 of the one-line delay circuit 5a is given via a compensation delay circuit 5f. The output 113 of the subtraction circuit 9a is output from the output terminal 3 as a luminance signal. Compensation delay circuits 5c, 5d, 5e, 5
f is a circuit for compensating the delay in each circuit.

FIG. 2 shows an embodiment of the image correlation judgment circuit 7. A / D
The output 101 of the converter 4, the output 102 of the 1-line delay circuit 5a, and the output 103 of the 1-line delay circuit 5b are given to the vertical low-pass filter 6d and the vertical band-pass filters 6f and 6g. The output 102 of the 1-line delay circuit 5a is the horizontal band pass filter 6i.
Given to. Vertical low pass filter 6d output 114
Is supplied to one input of a subtraction circuit 9b via a horizontal bandpass filter 6e and an absolute value circuit 10a. On the other hand, the output 120 of the vertical bandpass filter 6f is provided to the absolute value circuit 10b via the compensation delay circuit 5g. The compensation delay circuit 5g is a circuit for compensating for a delay in the horizontal bandpass filter 6e. The output of the absolute value circuit 10b is given to the other input of the subtraction circuit 9b and one input of the comparison circuit 11b. An output 117 of the subtraction circuit 9b is provided to one input of a comparison circuit 11a, and an output 118 (Kdy ₁ described later) of the constant generation circuit 12a is provided to the other input of the comparison circuit 11a. The other input of the comparison circuit 11b is connected to an output 123 of the constant generation circuit 12b (K
d ₁ ) is given.

The output 125 of the vertical band-pass filter 6g is provided to one input of the subtraction circuit 9c via the horizontal low-pass filter 6h and the absolute value circuit 10c. On the other hand, the output 131 of the horizontal bandpass filter 6i is provided to the absolute value circuit 10d via the compensation delay circuit 5h. The compensation delay circuit 5h is a circuit for compensating for a delay in the horizontal low-pass filter 6h. The output of the absolute value circuit 10d is given to the other input of the subtraction circuit 9c and one input of the comparison circuit 11d. The output 117 of the subtraction circuit 9c is given to one input of the comparison circuit 11c, and
An output 129 (Kdy ₂ described later) of the constant generation circuit 12c is provided to the other input of c. The other input of the comparison circuit 11d includes:
An output 134 (Kd ₂ described later) of the constant generation circuit 12d is provided.

At this time, for example, the vertical low-pass filter 6d is expressed as Fv l (Z) = (1/4) (1 + Z ^−l ) ² and the horizontal band-pass filter 6e has Fhh (Z) = 1− Z- ^4, that is, the frequency component corresponding to 1/2 of the color sub-carrier frequency in the horizontal direction is extracted, and the horizontal band pass filter 6i has Fdh (Z) = 1-Z. ^-4, and the vertical band pass filter 6g is expressed as Fvh (Z) = 1-Z ^-2l, that is, the frequency component corresponding to 1/2 of the color ^subcarrier frequency in the vertical direction is extracted. The horizontal low-pass filter 6h is expressed as Fhl (Z) = (1/4) (1 + Z ^-2 ) ₂ and the vertical band-pass filter 6f has Sdv (Z) = 1- It is a digital filter represented by Z ^-2l .

Outputs of the comparison circuits 11a and 11b are supplied to a vertical correlation detection circuit 13a, and outputs of the comparison circuits 11c and 11d are supplied to a horizontal correlation detection circuit 13b. The output 136 of the vertical correlation detection circuit 13a and the output 137 of the horizontal correlation detection circuit 13b are provided to the determination circuit 14. The output 110 of the judgment circuit 14 is sent out as the output of the image correlation judgment circuit 7.

FIG. 3 shows an example of the configuration of the determination circuit 14 shown in FIG.
The output 136 of the vertical correlation detection circuit 13a is given to one input of the NOR circuit 15. The output 137 of the horizontal correlation detection circuit 13b is
It is given to the other input of NOR circuit 15 and NOT circuit 16
Supplied to a. The output of the NOR circuit 15 and the output of the NOT circuit 16a become the output 110 of the image correlation determination circuit 7.

FIG. 4 shows another example of the configuration of the judging circuit 14. The output 136 of the vertical correlation detection circuit 13a is the exclusive NOR circuit 17
One input of the AND circuit 18 and one input of the AND circuit 18. The output 137 of the horizontal correlation detection circuit 13b is applied to the other input of the exclusive NOR circuit 17 and is also applied to the other input of the AND circuit 18 via the NOT circuit 16b. The output of the exclusive NOR circuit 17 and the output of the AND circuit 18 become the output 110 of the image correlation determination circuit 7.

 Next, the operation will be described.

The sampled sequence 101 of the NTSC composite color television signal sampled at the sampling frequency fs = 4fsc by the A / D converter 4 passes through delay circuits 5a and 5b, and thereby, is vertically aligned on the screen. Sample values at three sample points are obtained at the same time. That is, the composite color television signal (sample value) S (m, n) at the position of coordinates (m, n) is
02, the signal S (m, n-1)
Appears, and the signal S (m, n + 1) appears on the signal line 101 (see FIG. 6). A luminance signal color signal filter is constructed based on the sample values of the sample points over three lines on the screen.

In this method, color signals are extracted by the filter processing having the following transfer functions as the vertical color signal extraction filter 6a, the horizontal color signal extraction filter 6b, and the horizontal / vertical color signal extraction filter 6c.

Vertical color signal extraction filter Cv (Z) = (-1/4) (1-Z ^-l ) ² Horizontal color signal extraction filter Ch (Z) = (-1/4) (1-Z ^-2 ) ² Horizontal / vertical direction color signal extraction filter Chv (Z) = (-1/4) (1-Z- ² ) ² * (-1/4) (1-
Z- ^l ) ² The vertical filter output 104, the horizontal filter output 106, and the horizontal / vertical color signal extraction filter output 108 thus obtained are respectively sent to the switch circuit 8 via a compensation delay circuit.

Here, the operation of the circuit that determines which one of the color output signals of the vertical color signal extraction filter 6a, the horizontal color signal extraction filter 6b, and the horizontal / vertical color signal extraction filter 6c is selected will be described. .

With respect to the sample point of interest, the correlation between the images in the vertical and horizontal directions is detected, and when the correlation is particularly strong in the vertical direction, the output 105 of the vertical color signal extraction filter 6a is selected, and when the correlation is particularly strong in the horizontal direction, The switch circuit 8 is switched so that the output of the horizontal color signal extraction filter 6b is selected, and in other cases, the output of the horizontal / vertical color signal extraction filter is selected.

The detection of the image correlation and the control of the switch circuit 8 are performed by the image correlation determination circuit 7. Image correlation determination circuit 7
Then, the switch circuit 8 is controlled by the following operation.

The vertical decorrelation energy is Dv (Z), the horizontal decorrelation energy is Dh (Z), an absolute value approximation is introduced, and a transfer function is used to represent the following.

Dh (Z) = | 1−Z ^−2l | Dh (Z) = | 1−Z ⁻⁴ | The above two expressions are filter characteristics for blocking the DC component and the color subcarrier frequency component in the vertical and horizontal directions. Has become. In addition, the horizontal high frequency luminance signal energy is set to DYh.
(Z), the vertical direction high band luminance signal energy is DYv (Z), absolute value approximation is introduced, and it is expressed as follows using a transfer function.

DYh (Z) = | (1/4) (1 + Z ^-l ) ²・ (1-Z ^-4 ) | DYv (Z) = | (1/4) (1 + Z ^-2 ) ²・ (1-Z ^-2l ) | At this time, the vertical correlation detection circuit 13a determines that Dv (Z) ≦ Kd ₁ (Kd ₁ : correlation threshold constant) and DYh (Z) −Dv (Z) ≧ Kdy ₁ (Kdy ₁ : high frequency signal energy). Threshold value), it is determined that there is a correlation in the vertical direction, and a signal “1” is sent to the determination circuit 14. When Dv (Z)> Kd ₁ or DYh (Z) −Dv (Z) <Kdy ₁ , it is determined that there is no correlation in the vertical direction, and a signal “0” is sent to the determination circuit 14.

On the other hand, the horizontal correlation detection circuit 13b calculates Dh (Z) ≦ Kd ₂ (Kd ₂ : correlation threshold constant) and DYv (Z) −Dh (Z) ≧ Kdy ₂ (Kdy ₂ : high-band signal energy threshold constant) In the case of, it is determined that there is a correlation in the horizontal direction, and a signal “1” is sent to the determination circuit 14. If Dh (Z)> Kd ₂ or DYv (Z) −Dh (Z) <Kdy ₂ , It is determined that there is no correlation, and a signal “0” is sent to the determination circuit 14.

The determination circuit 14 controls the switch circuit 8 as follows according to the result of the above-described correlation detection.

That is, the relationship between the input and the output of the determination circuit 14 shown in FIG. 3 is as shown in FIG. At this time, the switch circuit 8
When the output of the NOR circuit 5 is "1", the switch is connected to the signal line 109 so that the output of the horizontal / vertical color signal extraction filter 6c flows. When the output of NOR circuit 5 is "0", NOR
The switch is switched by the output of the circuit 16a, and when it is "0", the output of the horizontal color signal extraction filter 6b is
When it is "1", the output of the vertical color signal extraction filter 6a is allowed to flow. Therefore, in the embodiment of FIG.
The output C (Z) of the switch circuit 8 switches as follows.

With horizontal correlation C (Z) = Ch (Z) Without horizontal correlation C (Z) = Cv (Z) if there is vertical correlation C (Z) = Chv (Z) if there is no vertical correlation In the determination circuit 14 shown in the figure, the input / output relationship is as shown in FIG. Like the output of the NOR circuit 15, the output of the exclusive NOR circuit 17 is used for turning on / off the output of the horizontal / vertical direction color signal extraction filter 6c in the switch circuit 8, and the output of the AND circuit 18 is used for the NOT circuit. Same as 16a output, horizontal filter 6b and vertical filter
Used for 6a selection. Therefore, in the circuit of FIG. 4, the output of the switch circuit 8 has a horizontal correlation and no vertical correlation C (Z) = Ch (Z) A vertical correlation and no horizontal correlation C (Z) = Cv (Z) When both horizontal and vertical correlations are present or when neither is present, C (Z) = Chv (Z). The color signal output of the switch circuit 8 is a compensation delay circuit.
The luminance signal 113 is subtracted from the composite video signal of the output 112
Is required.

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. However, it is possible to arrange the sample points in a grid on the screen. For example, the sampling is not limited to four times the color subcarrier and may be performed at another frequency.

Further, the digital filter used in the above embodiment is an example, and for example, the digital filter may be configured to have a higher order.

〔The invention's effect〕

As described above, according to the present invention, by the correlation between the vertical and horizontal images of a composite color television signal,
Since the luminance signal / chrominance signal separation filter is selectively used, it is possible to reduce the influence of leakage of the luminance signal and the chrominance signal to the mutual channels, and it is possible to reduce dot interference.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing a luminance signal color signal separation filter corresponding to an NTSC image correlation according to an embodiment of the present invention;
FIG. 2 is a block diagram showing an embodiment of the image correlation judging circuit, and FIGS. 3 and 4 are diagrams showing first and second embodiments of the judging portion of the image correlation judging circuit, respectively. Fig. 6 is a schematic block diagram showing an example of a conventional luminance signal / chrominance signal separation filter, and Fig. 6 is an arrangement on the screen of a signal sequence in which an NTSC composite color television signal is synchronously sampled at four times the color subcarrier. 7 is a diagram showing the input / output relation of the determination portion shown in FIG. 3, and FIG. 8 is a diagram showing the input / output relation of the determination portion shown in FIG. 1 …… input terminal, 2,3 …… output terminal, 4 …… A / D converter,
5a ~ 5k ... delay circuit, 6a ~ 6k ... digital filter,
7 image correlation determining circuit, 8 switch circuit, 9a to 9d
…… Subtraction circuit, 10a to 10d …… Absolute value circuit, 11a to 11d…
Comparing circuit, 12a to 12d ... Constant generating circuit, 13a ... Vertical correlation detecting circuit, 13b ... Horizontal correlation detecting circuit, 14 ... Judgment circuit, 15 ... NOR circuit, 16a, 16b ... NOT circuit, 17 ... … Exclusive NOR circuit, 18 …… AND circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (5)

(57) [Claims] 1. A composite video signal sampled at a predetermined frequency synchronized with a horizontal scanning frequency so that each sample point is arranged on a grid on a screen, and a luminance signal component is digitally converted from the composite video signal. A color signal separation filter for separating an image correlation corresponding luminance signal and a color signal component, wherein the composite image signal is delayed so as to separate a luminance signal and a color signal from each other, and the target sample point on the screen. And delay means for simultaneously obtaining sample values of a plurality of reference sample points that are aligned on a straight line in the vertical direction, and a sample value of the target sample point and a predetermined reference sample point as inputs, and a vertical color subcarrier. A vertical color signal extraction filter that extracts and outputs a frequency component corresponding to the component of at least the sample value of the sample point of interest, and extracts a frequency component corresponding to a component of a horizontal color subcarrier. And a horizontal color signal extraction filter for inputting the sample values of the sample point of interest and a predetermined reference sample point, and a horizontal direction for extracting and outputting a frequency component corresponding to a color subcarrier component in both the vertical and horizontal directions.・ A vertical color signal extraction filter and the sample values of the sample point of interest and a predetermined reference sample point are input, and signal changes in the horizontal and vertical directions are detected, and the signal change in the vertical direction is smaller than a constant K1. , And vertical correlation detection means for determining that there is a correlation in the vertical direction when the change in the horizontal direction is greater than the change in the signal in the vertical direction plus a constant K2, the sample point of interest and the predetermined reference sample point The signal value in the horizontal and vertical directions is detected by inputting the sample value of, and the signal change in the horizontal direction is smaller than the constant K3, and the change in the vertical direction is added to the signal change in the horizontal direction by a constant K4. It's something When there is a large correlation, the horizontal correlation detecting means for determining that there is a correlation in the horizontal direction, the determination result of the vertical correlation detecting means and the determination result of the horizontal correlation detecting means are input, and the presence or absence of the correlation in the horizontal and vertical directions is determined. Determination means for transmitting a control signal for selecting an output of the horizontal color signal extraction filter, the vertical color signal extraction filter, or the horizontal / vertical color signal extraction filter according to the determination result; Means for outputting a color signal component according to a control signal of the means, and a subtraction circuit for subtracting the output of the switch circuit from the composite video signal to output a luminance signal component Luminance signal and color signal separation filter. 2. The vertical correlation detecting means uses the absolute value of the output of a vertical bandpass filter having a center frequency of 1/2 of a color subcarrier as the signal change in the vertical direction, and as the signal change in the horizontal direction, It is characterized by using the absolute value of the output of a two-dimensional filter composed of a cascade connection of a vertical low-pass filter that removes a color subcarrier and a horizontal bandpass filter whose center frequency is 1/2 of the color subcarrier. An image correlation-compatible luminance signal / color signal separation filter according to claim 1. 3. The horizontal correlation detecting means uses the absolute value of the output of a horizontal bandpass filter having a center frequency of 1/2 of the color subcarrier as the horizontal signal change, and the vertical signal change as It is characterized by using the absolute value of the output of a two-dimensional filter composed of a cascade connection of a horizontal low-pass filter that removes a color subcarrier and a vertical bandpass filter whose center frequency is 1/2 of the color subcarrier. An image correlation-compatible luminance signal / color signal separation filter according to claim 1. 4. The determination means sends a control signal for selecting a horizontal color signal extraction filter output when there is a correlation in the horizontal direction, and when there is no correlation in the horizontal direction but a correlation in the vertical direction, It sends a control signal for selecting the vertical color signal extraction filter output, and sends a control signal for selecting the horizontal / vertical color signal extraction filter output when there is no correlation in the horizontal and vertical directions. An image correlation-corresponding luminance signal / color signal separation filter according to claim 1. 5. The determining means sends a control signal for selecting a vertical color signal extraction filter output when there is a correlation in the vertical direction and no correlation in the horizontal direction, and there is a correlation in the horizontal direction. If there is no correlation in the vertical direction, the control signal for selecting the output of the horizontal color signal extraction filter is sent. If there is a correlation in the horizontal direction and the vertical direction, or there is no correlation, the horizontal / vertical color signal The image correlation corresponding luminance signal color signal separation filter according to claim 1, wherein a control signal for selecting an extraction filter output is transmitted.