JPH03187697A - Yc separation circuit - Google Patents

Abstract

PURPOSE:To perform YC separation with superior picture quality by expanding the band area of a BPF(band-pass filter) for chrominance signal separation only at the horizontal edge part of a luminance signal and when the correlation of chrominance in a perpendicular direction exists. CONSTITUTION:A correlation detector 5 which detects the correlation of a chrominance signal among three lines, a selection circuit 12 which selects one output from three kinds of filter output obtained by filtering a digital video signal band-Iimited with the BPF 2 based on the output of the correlation detector 5, a detector 6 which detects the edge in the horizontal direction of a present line not receiving hand limitation, an AND circuit 7 which takes the AND of the output of the detector 5 and that of the edge detector 6, the band-pass filter 13 which limits the output of the selection circuit 12 to a band narrower than that in the band limitation of the BPF 2, and a switch 15 which switches the output of the band-pass filter 13 or that of a delay circuit 14 based dn the output of the AND circuit 7 are provided. Then, the band area of the BPF is expanded only when the correlation of the chrominance signal exists in the perpendicular direction and also, it is at the edge. In such a way, it is possible to improve picture quality after performing the YC separation.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applicable to an apparatus that separates a composite video signal into a luminance signal and a color signal, and then displays or records a color video signal. The present invention relates to a YC separation circuit that can perform

Conventional technology Generally, when displaying a composite video signal on a color monitor,
It is necessary to separate the luminance signal and color signal which are frequency interleaved in the video signal. As circuits for this separation, circuits based on frequency separation and circuits using comb-shaped filters have conventionally been used. In addition, with the recent development of digital technology, semiconductor memory is used to detect the presence or absence of vertical correlation from information on three lines, and a band pass filter (hereinafter referred to as BPF) and a comb between the lines are used. Type filters that can be used selectively are being used.

The configuration will be explained below with reference to FIG.

As shown in the figure, a digital video signal input from a terminal 101 is input to a BPF 102.

In the BPF 102, the input digital video signal is band-limited around the color subcarrier frequency, is input to a one-line memory (hereinafter referred to as IH memory) 103, and is delayed by one line's time.IH The output of memory 103 is further input to IH memory 104 and delayed by one line time.

The output of BPF 102 and the output of IH memory 103 are input to subtracter 10B. In the subtracter 106, this 2
The two inputs are subtracted and input to the coefficient unit 109. In the coefficient unit 109, the signal is multiplied by 1/2 and inputted to the selection circuit 110.

Further, the output of IH memory 103 and the output of IH memory 104 are input to subtracter 107 . The subtracter 107 subtracts these two inputs and inputs the result to the coefficient unit 108. In the coefficient multiplier 108, it is multiplied by 172 and the selection circuit 11
It is input to 0.

Further, the output of the IH memory 103 is input to the selection circuit 110.

On the other hand, the output of BPF 102 and IH memory 103°104
is input to the correlation detector 105.

In the correlation detector 105, the output of the IH memory 103 is used as the current line, and a selection signal is output to the selection circuit 110 depending on the presence or absence of correlation between the previous and next lines.

In the selection circuit 110, depending on the output of the correlation detector 105, if the correlation is strong, the output of the coefficient unit 108 or the coefficient unit 1 is selected.
The output of the IH memory 103 is selected and output from the IH memory 103 if the correlation is weak.

The output of the selection circuit 110 is outputted from a terminal 113 as a separated color signal.

Further, the digital video signal inputted from the terminal 101 is inputted to the delay 111, delayed so that the time timing matches the output of the selection circuit 110, and inputted to the subtracter 112. A subtracter 112 subtracts the separated color signal output from the selection circuit 110 from the output of the delay 111, and outputs the separated color signal to the terminal 114 as a luminance signal from which the color signal is separated.
is output from.

Problems to be Solved by the Invention In such conventional YC separation circuits, when a luminance signal and a color signal change simultaneously, such as a color par signal, a part of the color signal is treated as a luminance signal, and a part of the color signal is treated as a luminance signal. A disturbance occurs. As a countermeasure, it is possible to make it less noticeable by widening the BPF band. However, B.P.F.
When the band is widened, the horizontal resolution of the luminance signal decreases, so
It was not possible to widen the BPF band much.

The present invention solves the above-mentioned conventional problems, and
It is an object of the present invention to provide a YC separation circuit in which the separation circuit has less dot interference and the deterioration of horizontal resolution is not noticeable.

Means for Solving the Problems In order to achieve the above object, the present invention inputs the current line of a digital video signal whose band is limited around the color subcarrier and the signals of the lines before and after it, and calculates the color between three lines. a correlation detector for detecting the correlation of signals; a selection circuit for selecting one output from three types of filter outputs obtained by filtering the band-limited digital video signal using the output of the correlation detector; a detector that detects edges in the horizontal direction of the current line that are not received; an AND circuit that takes the logical product of the output of the correlation detector and the output of the edge detector;
A band-pass filter that limits the output of the selection circuit to a band narrower than the band limit, a delay that delays the output of the selection circuit by the same amount as the delay amount of the band-pass filter, and an AND of the output of the band-pass filter or the delay. It has a configuration with a switch that is switched by the output of the AND circuit based on the output of the circuit.

Effects With the above-described configuration, the present invention widens the BPF band only when there is a correlation between color signals in the vertical direction and there is an edge, so it is possible to improve the image quality after YC separation.

EXAMPLE Hereinafter, a YC separation circuit according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main part configuration of a YC separation circuit in one embodiment of the present invention.

In FIG. 1, a digital video signal input from terminal 1 is input to BPF 2, and is limited to a band M (Hz) centered around color subcarrier frequency Fsc. This situation is shown in FIG. 2(a). The output of the BPF 2 is input to the IH memory 3 and is delayed by one line time. The output of the IH memory 3 is input to the IH memory 4 and further delayed by one line time.

The output of the BPF 2 and the output of the IH memory 3 are input to a subtracter 8, and after being subtracted, are input to a coefficient unit 11. Coefficient unit 1
1 and is multiplied by 1/2 and inputted to the selection circuit 12 as the output of the comb-shaped filter with the rear line. Further, the output of the IH memory 3 and the output of the IH memory 4 are input to a subtracter 9, and after being subtracted, are input to a coefficient unit 10. Coefficient unit 10
The signal is multiplied by 172 at , and input to the selection circuit 12 as the output of the comb-shaped filter with respect to the previous line. Further, the output of the IH memory 3 is input to the selection circuit 12 as the output of the BPF 2 of the current line.

That is, in the selection circuit 12, the signal band-limited by the BPF 2 is filtered by a digital filter consisting of an IH memory 1J3.4, a subtracter 8.9, and a coefficient unit 10.11, and the filtered three types of filters, The configuration is such that the output is input.

On the other hand, the output of the BPF 2 and the outputs of the IH memories 3 and 4 are input to the correlation detector 5. In the correlation detector 5, IH
It is detected whether or not there is a correlation in color signals between the output of the memory 3, the output of the IH memory 4 which is a signal before IH, and the output of BPF 2 which is a signal after 1H. The result is output to the selection circuit 12 as, for example, 2-bit information. At the same time, the upper bits of this 2-bit information are output to the AND circuit 7.

The 2-bit information output from the correlation detector 5 is the previous line,
If there is a correlation between either of the subsequent lines and the current line, the upper bit is set to "1", and if there is no correlation between them, it is set to rOJ. Further, the lower bit is set to "O" if there is a correlation only in the previous line, and is set to "1" if there is a correlation in the next line regardless of whether there is a correlation in the previous line.

In the selection circuit 12, if the upper bit of the output of the correlation detector 5 is "O high", that is, the 2-bit information is a signal of "O9 undefined", the selection circuit 12 selects the output (BPF) of the IH memory 3.
If rl, OJ, select the output of the coefficient unit 10 (comb-shaped filter with the previous line), and if rl, IJ, select the output of the coefficient unit 11 (comb-shaped filter with the subsequent line).

The output of the selection circuit 12 is input to a BPF13 having frequency characteristics as shown in FIG. 2(b) and a delay 14 having the same amount of delay as the BPF13.

In the BPFI 3, the signal is limited to the band N (Hz) and is input to the switch 15. Here, the passband M of BPF2
(Hz) and the passband N (Hz) of BPFl3,
Let it be MAN.

Further, in the delay 14, the signal is input to the switch 15 as a signal delayed by the same amount as the delay amount of the BPF13. Here, the output of the delay 14 has a band M (Hz).

On the other hand, the digital video signal input from terminal 1 is
The signal is input to the H memory 16 and delayed by one line time. I
The output of the H memory 1B is input to the edge detector 6. The edge detector 6 detects edges in the horizontal direction of the luminance signal and outputs "1" only at the edge portions. The output of the edge detector 6 is input to an AND circuit 7, and is ANDed with the upper bit of the output of the correlation detector 5. and,
When both are "1", that is, it is an edge portion and there is a correlation of color signals, "1" is output.

The output of the AND circuit 7 is input to the switch 15, and
When the output of circuit 7 is "1", the output of delay 14 is
When it is "O", the output of BPFl3 is output.

The output of the switch 15 is output from the terminal 18 as a separated color signal.

Further, the output of the switch 15 is input to the subtracter 17, and l
The signal is subtracted from the digital video signal output from the H memory 16, and the color signal is output from the terminal 19 as a separated luminance signal.

As described above, according to this embodiment, by taking the logical product of the output of the edge detector 6 and the output of the correlation detector 5, it is possible to detect that there is an edge in the horizontal direction and the correlation of the color signals in the vertical direction. The band of the BPF for color signal separation can be widened only in certain cases.

Effects of the Invention As is clear from the above embodiments, according to the present invention, the band of the BPF for color signal separation is widened only when there is a color correlation in the vertical direction in the horizontal edge portion of the luminance signal. By doing so, there is less dot interference, and in other places B
Since the band of the PF is not so wide, it is possible to provide a YC separation circuit with good image quality without degrading the horizontal resolution of the luminance signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a YC separation circuit according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of a BPF in this embodiment, and FIG. 3 is a block diagram of a conventional YC separation circuit. 2, 13... BPF, 3, 4. 18...I
H memory, 5... Correlation detector, 6... Edge detector, 7... AND circuit, 8. 9. 17
...Subtractor, 12...Selection circuit, 14...Delay, 16...Switch.

Claims (1)

[Claims] A signal of a currently processed line of a digital video signal whose band is limited around the color subcarrier frequency and signals of lines before and after it are input to detect the correlation of color signals between the three lines. a correlation detector; a selection circuit that selects one output from three types of filter outputs obtained by filtering the band-limited digital video signal using the output of the correlation detector; an edge detector that detects a horizontal edge of a line signal; an AND circuit that takes an AND of the output of the correlation detector and the output of the edge detector; and an output of the selection circuit that is narrower than the band limit. a bandpass filter that limits the band; a delay that delays the output of the selection circuit by the same amount as the delay amount of the bandpass filter; and an output of the AND circuit that switches between the output of the bandpass filter and the output of the delay. A YC separation circuit characterized by comprising a switch.