JPH0468838B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides a YC separation filter for extracting a luminance signal (hereinafter referred to as Y signal) or a color signal (hereinafter referred to as C signal) from an NTSC signal in an NTSC color television. It is related to
After analog NTSC signals are A/D converted, YC separation is performed digitally.

First, the signal sequence S(i,j) (i=1, 2, 3, . . . when the analog NTSC signal is digitized)
m, and j=1, 2, 3, . . . n) are shown in FIG. The sampling frequency f _s at this time is usually selected to be four times the color subcarrier frequency f _sc . In FIG. 1, the Y signal and C signal of sample S(i,j) have the following relationship.

S(i,j)=Y(i,j)+C(i,j) Further, a normal television signal has a property that there is a strong correlation between adjacent samples in the horizontal and vertical directions within one field. Furthermore, since the NTSC system uses interlaced scanning, the phase of the C signal is inverted line by line and every two samples, as shown in FIG. Utilizing this property, YC separation can be performed digitally.

Figure 3 shows the configuration of a conventional YC separation filter.
In the figure, 1 is an A/D converter that digitizes an analog NTSC signal 101, and 2 is a line alternating signal H _C 103 H _C =D from the output 2 of this A/D converter.
+C and D represent vertical high frequency components and horizontal low frequency components of the Y signal), and 3 is a horizontal low frequency component for the output 103 of the vertical filter. 4 is a delay element for compensating the delay in filters 2 and 3, and 5 is a band pass filter 3 for removing the C signal 105.
This subtracter calculates the difference between the output 105 of the delay element 4 and the output 106 of the delay element 4.

Next, the operation of this YC separation filter will be explained. The analog NTSC signal 101 is converted to a predetermined sampling frequency f _s (f _s =4f _sc ) using the A/D converter 1.
Samples are extracted and digitized, and a digital signal sequence s(i,j) (i=1, 2, 3, . . .
m, and j=1, 2, 3, . . . n) 102. This digital signal sequence s(i,j)10
2 is first waved by a vertical filter 2. Next, the configuration and operation of the vertical filter 2 will be explained.

A specific configuration of the vertical filter 2 is shown in FIG. In the figure, 6 is a line buffer memory that delays the input signal 102 by one line, and 7 is an A/
An adder that adds the output 102 of the D converter 1 and the output 108 of the line buffer memory 6, 8 is an adder 7
9 is a multiplier that multiplies the output 109 of line buffer memory 6 by 1/2, 10 is an output 110 of multiplier 8
This is a subtracter that calculates the difference between the output 111 of the multiplier 9 and the output 111 of the multiplier 9.

The operation of vertical filter 2 is as follows: Line alternating signal H _C at sample S(i,j)
(i, j), S(i, j-1) 108, S(i,
Three samples: j) 104 and S(i,j+1) 102 are used. That is, sample S(i,j)
When focusing on , H _C (i, j) 103 is obtained by executing the following calculation using the values of samples at positions one line apart in the upper and lower directions.

H _C (i,j)=-1/4S(i,j
-1)+1/2S(i,j)-1/4S(i,j+1)
As a result, the vertical low frequency component of the Y signal in sample S(i,j) is removed. Then, this H _C signal 103 is passed through the band pass filter 3
is input to the horizontal low frequency component D of the Y signal.
is removed, and as a result, the D component is removed from the H _C signal, so the C signal 105 at sample S(i,j) is found. Further, the Y signal 107 at this time is determined by the following equation as the difference between the output signal 106 of the delay element 4 and the c signal 105.

(107) Y (i, j) = S (i, j) - C (i, j) Since the conventional YC separation filter is configured as described above, when the television signal changes in the horizontal direction, The energy of the horizontal high frequency component of the Y signal increases, and this horizontal high frequency component exists in the same frequency band as the H _C signal.
Since it is difficult to provide a blocking characteristic excluding the Y signal, the horizontal high frequency component of the Y signal remains in the H _C signal. Therefore, as a result, YC
The separation characteristics are impaired, and the output Y signal 107 becomes mixed with the C signal component. Furthermore, the horizontal high frequency components of the Y signal that were not removed are
This YC signal remains and affects the H _C signal.
The separation filter output has the disadvantage of poor response to changes in the television signal in the vertical direction.

The purpose of this invention is to eliminate the drawbacks of the conventional systems as described above, and to eliminate the influence of the horizontal high frequency components and vertical high frequency components of the Y signal even with respect to local changes in the composite television signal. The purpose of this invention is to be able to separate luminance signals and color signals with high accuracy without any interference, and to suppress a decrease in resolution, that is, a blurring of an image.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 5, 1 is an A/D converter that converts an analog NTSC signal 101 into a digital signal, 11 is a vertical and horizontal direction selective filter that removes the Y signal component from the output 102 of this A/D converter 1, and 4 is this vertical/horizontal selection type filter 1
1 is a delay element for compensating for the delay in 1; 5 is the output 105 of the vertical/horizontal selective filter 11;
This is a subtracter that calculates the difference between the output 106 of the delay element 4 and the output 106 of the delay element 4.

This delay element 4 and subtracter 5 constitute a luminance signal deriving circuit.

Next, the operation of the YC separation filter in this invention will be explained. Digital signal sequence S(i,j)1 digitized by A/D converter 1
02 is a vertical and horizontal selection filter 11.
waved by. The configuration and operation of this vertical and horizontal filter 11 are as follows.

The configuration of the vertical and horizontal direction selection filter 11 is shown in FIG. In the figure, 6 is an input signal 102,
A line buffer memory 113 delays the input signals by one line, a sample buffer memory 12 delays the input signals 102, 104, and 113 by two samples, and the line buffer memory 6 and the sample buffer memory 12 constitute an extraction circuit. are doing.

7a is a second adder that adds the output 114 of the line buffer memory 6 and the output 112 of the sample buffer memory 12; 8a is the second adder 7a;
a second multiplier that multiplies the output 117 of by 1/4;
9 is a third multiplier that multiplies the output 113 of the sample buffer memory 12 by 1/2, and 10a is a third multiplier that calculates the difference between the output 119 of the second multiplier 8a and the output 116 of the third multiplier 9. The second adder 7a, the second multiplier 8a, the third multiplier 9, and the second subtracter 10a constitute a second filter.

7b is a first adder that adds the output 104 of the line buffer memory 6 and the output 115 of the sample buffer memory 12; 8b is the first adder 7b;
a first multiplier that multiplies the output 118 of by 1/;
0b is a first subtracter that calculates the difference between the output 120 of the first multiplier 8b and the output 116 of the third multiplier 9, and this first adder 7b and the first multiplier 8
b, the third multiplier 9, and the first subtractor 10b constitute a first filter.

13 is the output 104 of the line buffer memory 6;
114 and the output 11 of the sample buffer memory 12
5 and 112, respectively, a subtracter 14
15 is an absolute value calculator that calculates the absolute values of the outputs 123 and 124 of the subtracter 13, and 15 is a comparator that compares the outputs 125 and 126 of the absolute value calculator 14 and operates the changeover switch 16. 1
3, the absolute value calculator 14, and the comparator 15
constitute a comparison decision circuit. 16 as the C signal 105, the second and first subtracters 10a, 10
This is a changeover switch for taking out either output 121 or 122 of output 121, and this changeover switch 16 serves as a selector.

Next, the operation of this vertical and horizontal direction selective filter will be explained.

A certain sample composite signal S(i,j) of the signal sequence digitized by the A/D converter 1
is a luminance signal (hereinafter referred to as Y signal) Y(i,j)
and color information (hereinafter referred to as C signal) C
(i, j) is expressed as follows.

S(i,j)=Y(i,j)+C(i,j) We now assume that the sampling frequency is four times the frequency of the color subcarrier, as is often used. In order to find the value of this C signal C(i,j), sample S(i,j)(○†g

Claims (1)

[Scope of Claims] 1. A specific sampled signal X to be processed out of a signal sequence obtained by sampling a composite television signal, and a color of the specific sampled signal X on the same line as the specific sampled signal Two horizontal sampling signals L and R that are in an antiphase relationship with the phase of the subcarrier and are symmetrical in position with respect to the specific sampling signal.
and positions that are in an opposite phase relation to the phase of the color subcarrier of the specific sampling signal X in the upper and lower lines of the specific sampling signal X, and are vertically symmetrical with respect to the specific sampling signal X. an extraction circuit for extracting two related vertical sampling signals U and D; and the horizontal sampling signal R and the horizontal sampling signal L of the composite television signal state extracted by the extraction circuit. and the difference between the vertical sampling signal U and the vertical sampling signal D of the composite television signal state, and comparing two absolute values derived from the difference, and comparing these two absolute values. a comparison and determination circuit that outputs a selection signal for selecting a sampling signal in a direction corresponding to a smaller value among them; a first filter for extracting a chrominance signal based on the values of the directional sampling signals L, R; a second filter that extracts a color signal based on the values of the direction sampling signals U and D; and a comparison and determination circuit that outputs one of the outputs of the first filter and the second filter. a selector that selects in response to a selection signal; and a selector that selects a specific sampled signal X of the composite television signal based on a difference between the selected output selected by the selector and the specific sampled signal X of the composite television signal state. 1. A color signal separation circuit for a composite television signal, comprising: a luminance signal deriving circuit for deriving a luminance signal contained in a composite television signal.