JP2789613B2 - Comb filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a comb filter used for separating a luminance signal and a chroma signal in a color TV or VTR.

[Summary of the Invention] The present invention relates to a comb filter, in which first and second delay lines are connected in series, input and output terminals of these delay lines are respectively connected to subtraction circuits, and input and output terminals of the delay lines are connected. By detecting the vertical correlation from the signal and extracting the subtraction output on the side with the higher correlation, a good separation output can be obtained.

[Conventional technology]

For example, in the case of separating a luminance signal and a chroma signal from a NTSC color video signal, a method of separating the luminance signal and the chroma signal using a band-puff filter has been conventionally used in many cases. However, in this case, for example, 3.58MHz ± 500kHz
Since all luminance signals included in the band of the luminance signal are regarded as chroma signals, high-frequency components of the luminance signal are mixed into the chroma signal in a portion where the luminance signal changes sharply, and image degradation called cross color occurs. .

On the other hand, a so-called comb filter has been proposed that utilizes the vertical correlation of the screen and the fact that the phase of the subcarrier of the chroma signal is inverted every horizontal period. FIG. 6 shows a circuit in which a signal from an input terminal (101) is supplied to a delay line (1H DL) (102) for one horizontal period, and a signal at an input / output end of the delay line (102) is subtracted. It is supplied to the circuit (103). As a result, a signal in which the luminance signal has been canceled is extracted from the subtraction circuit (103), and this signal is supplied to a band-pass filter (BPF) (104), and the separated chroma signal is extracted to an output terminal (105). Is done. Input terminal (10
The signal from 1) passes through a delay line (DL) (106) corresponding to a signal delay of a band-pass filter (104) or the like, and a subtraction circuit (1).
07), the chroma signal from the bandpass filter (104) is supplied to the subtraction circuit (107), and the luminance signal from which the chroma signal has been removed is taken out to the output terminal (108).

[Problems to be solved by the invention]

However, in this case, for example, in a scanning line having no vertical correlation of the luminance signal, a luminance signal remains, and when there is a band component near the chroma signal in the luminance signal, a cross color similar to the related art occurs. There is a risk. In a scan line having no vertical correlation of the chroma signal, the level of the chroma signal of the changed scan line is reduced, and the vertical resolution of the chroma signal is deteriorated.

In view of such a point, the present application provides a comb filter free of the above-described signal degradation.

[Means for solving the problem]

In the present invention, the first means is to convert the composite video signal to the first serially connected first video signal having a delay time of one horizontal period.
And second delay lines (2) and (3), and input / output signals of the first and second delay lines to first and second subtraction circuits (4) and (5), respectively. At the same time, the input / output signal of the first delay line and the output signal of the second delay line are respectively converted into filter circuits (6) to (8) and absolute value circuits (9) to (9).
(11) and supplied to the logical operation unit (15) through the binarization circuits (12) to (14), the input / output signal of the first delay line binarized by the logical operation unit, and the A logic operation is performed on the output signal of the second delay line according to a predetermined truth table, and the output signal of the first and second subtraction circuits is selected (switch (18)) by the logical operation output and extracted. Filter.

The second means is the first means, wherein the input / output signals of the first and second delay lines are respectively sent to first and second adders (31) and (32) via the filter circuit. And the output signals of the first and second adder circuits are supplied to a logical operation unit through absolute value circuits (33) and (34) and binarization circuits (35) and (36). The output signals of the first and second addition circuits, the input / output signals of the first delay line, and the output signals of the second delay line, which have been binarized, are logically operated according to a predetermined truth table. And a comb filter for selecting and taking out the output signals of the first and second subtraction circuits based on the logical operation output.

[Action]

According to this, the vertical correlation is detected from the signals at the input and output terminals of the first and second delay lines, and the subtraction output on the side with the higher correlation is selected, thereby obtaining a good separation output. be able to.

〔Example〕

In FIG. 1, the luminance signal “Y” from the input terminal (1)
And a chroma signal "C" are combined into first and second delay lines (1H
DL) is supplied to the series circuit of (2) and (3). The signals at the input / output terminals of these delay lines (2) and (3) are supplied to first and second subtraction circuits (4) and (5), respectively.

Also, the signals at the input / output terminals of the delay lines (2) and (3) are band-pass filters (BPF) (6), (7) and (8), respectively.
Supplied to Outputs of these filters (6) to (8) are absolute value circuits (ABS) (9), (10), and (11), respectively.
The absolute value is supplied to a logical operation unit (15) through coring circuits (12), (13), and (14) for comparing the absolute value with a predetermined potential and binarizing.

On the other hand, subtraction outputs of the subtraction circuits (4) and (5) are supplied to band-pass filters (16) and (17), respectively, to extract signals corresponding to chroma signals. To the first and second fixed contacts.

Then, the coring circuit (1)
With the outputs of (2), (13), and (14) as, respectively, a logical operation based on the following truth table is performed, and the switch (18) is controlled according to the calculated output.

The signal from the switch (18) controlled by this is taken out to the chroma signal output terminal (19).

A signal from the output terminal of the delay line (2) is supplied to a subtraction circuit (21) through a delay line (DL) (20) corresponding to a signal delay of a band-pass filter (16) or (17). The chroma signal from the switch (18) is supplied to the subtraction circuit (21), and the luminance signal from which the chroma signal has been removed is output to the output terminal (22).

Therefore, in this circuit, for example, when the level of the luminance signal changes in the middle of the scanning line and a signal having no vertical correlation is supplied to the input terminal (1), the signal of each section becomes as shown in FIG. Here, the waveform in the figure shows a luminance signal component near the chroma signal. In the outputs a to c of the band-pass filters (6) to (8), for example, if a luminance signal component exists only in two horizontal periods, an in-phase signal is extracted in these periods. Note that b and c are each delayed by one horizontal period.

Further, these signals a to c are used as absolute value circuits (9) to (1).
When supplied to 1), a signal appears on the scanning line where the luminance signal component exists, and the outputs of the coring circuits (12) to (14) become "1".

On the other hand, the signals from the subtraction circuits (4) and (5) remain at half their levels on the scanning lines having no vertical correlation, and conventionally, these signals are taken out to generate a cross color or the like. I was On the other hand, in the above-described embodiment, (,,) =
By extracting the signals at (1,0,0) and (0,1,1), a chroma signal "C" having no luminance signal component remains as shown in the output terminal (19). Be taken out.

That is, the extracted chroma signal "C" is completely equal to the original chroma signal component contained in the output of the delay line (2), thereby preventing the occurrence of cross color and the like, and furthermore, these signals are subtracted by the subtraction circuit (21). Is supplied to the output terminal (22), and a good luminance signal "Y" without deteriorating the vertical resolution is taken out from the output terminal (22).

In the case of a signal in which the level of the luminance signal is constant and a chroma signal is added from an intermediate scanning line, the signals of the respective parts are as shown in FIG. The vertical resolution of the signal has deteriorated. On the other hand, by making selection using the signals,, it is possible to extract a chroma signal "C" without deterioration as shown in the figure.

Thus, according to the above-described apparatus, the vertical correlation is detected from the signals at the input and output terminals of the first and second delay lines, and the subtraction output on the side with the strong correlation is selected, whereby good separation can be achieved. You can get the output.

In the above-described circuit, for example, when a signal in which the level of a luminance signal is constant and the phase of a chroma signal is inverted (changes to a complementary color) from an intermediate scanning line is supplied to the input terminal (1), this change is caused. Since there is no vertical correlation of the chroma signal in the scanned line, the signal is deteriorated. That is, in this case, the chroma signal taken out to the output terminal (19) is degraded, so that the luminance signal taken out to the output terminal (22) has a chroma signal remaining on the changed scanning line and causes so-called dot disturbance. Cause it to occur.

FIG. 4 solves such a problem. In FIG. 4, the outputs of the band-pass filters (6) to (8) are supplied to first and second adders (31) and (32). The addition outputs of the adder circuits (31) and (32) are absolute value circuits (33) and (34), respectively, and the coring circuits (35) and (36) which compare the absolute value with a predetermined potential to binarize. ) Is supplied to the logical operation unit (15) together with the outputs of the coring circuits (12) to (14). Other circuit configurations are the same as in the first embodiment.

Then, the coring circuit (3)
Using the outputs of (5) and (36) as, respectively, a logical operation based on the following truth table is performed together with the above and, and the switch (18) is controlled according to the calculated output.

That is, in this example, a signal corresponding to the decorrelation of the chroma signal is extracted from the addition circuits (31) and (32),
By selecting the output on the "0" side, better separation can be performed.

That is, FIG. 5 shows a signal of each section when a signal in which the level of the luminance signal is constant and the phase of the chroma signal is inverted (changes to a complementary color) from an intermediate scanning line is supplied to the input terminal (1). Is shown. Here, the waveform in the figure indicates the phase of the chroma signal. And the band pass filter (6)
In the outputs a to c of (8), for example, if the phase is inverted at the position indicated by the broken line, the phase that should be inverted every one horizontal period is continued in the same phase. Note that b and c are each delayed by one horizontal period.

Further, these signals a to c are added to adders (31) and (32).
, A signal appears at the addition output on the scanning line whose phase is inverted, and the outputs of the coring circuits (35) and (36)
Becomes “1”.

On the other hand, the signals from the subtraction circuits (4) and (5) lose their subtraction output on the scanning line whose phase is inverted, and conventionally, these signals are extracted to cause dot disturbance or the like. On the other hand, in the above embodiment, the logical operation unit (15)
By extracting the signal only when (,) = (0,1) by the function of (1), the chroma signal "C" as shown in the figure is extracted from the output terminal (19).

That is, the extracted chroma signal "C" is exactly equal to the chroma signal component included in the output of the delay line (2),
By supplying these signals to the subtraction circuit (21), a luminance signal "Y" from which dot interference has been removed is taken out at the output terminal (22).

It should be noted that processing for the other signal changes is performed in the same manner as in the first embodiment.

Thus, in this example, a better separation output can be obtained.

〔The invention's effect〕

According to the present invention, the vertical correlation is detected from the signals at the input and output terminals of the first and second delay lines, and the subtraction output on the side with the higher correlation is selected, whereby a good separation output is obtained. You can now take it out.

[Brief description of the drawings]

FIG. 1 is a block diagram of one example of the present invention, FIGS. 2 and 3 are diagrams for explaining the same, FIG. 4 is a block diagram of another example, FIG. FIG. 6 is a diagram for explaining a conventional technique. (1) is an input terminal, (2), (3) and (20) are delay lines,
(4) (5) (21) are subtraction circuits, (6) to (8) (16)
(17) is a band pass filter, (9) to (11) (33)
(34) is an absolute value circuit, (12) to (14) (35) and (36) are coring circuits, (15) is a logical operation unit, (18) is a switch, (19) and (22) are output terminals, (31) and (32) are addition circuits.

Claims (2)

(57) [Claims] A composite video signal is supplied to serially connected first and second delay lines each having a delay time of one horizontal period, and input / output signals of the first and second delay lines are respectively supplied. In addition to supplying the signals to the first and second subtraction circuits, the input / output signal of the first delay line and the output signal of the second delay line are supplied to a logical operation unit through a filter circuit, an absolute value circuit, and a binarization circuit, respectively. The input / output signal of the first delay line and the output signal of the second delay line, which have been binarized by the logical operation unit, are logically operated according to a predetermined truth table. A comb filter which selectively takes out output signals of the first and second subtraction circuits. 2. The method according to claim 1, wherein input and output signals of the first and second delay lines are supplied to first and second adders via the filter circuit, respectively. The output signals of the first and second adder circuits are supplied to a logical operation unit through an absolute value circuit and a binarization circuit, and the outputs of the first and second adder circuits binarized by the logical operation unit Signals, input / output signals of the first delay line and output signals of the second delay line are logically operated according to a predetermined truth table, and output signals of the first and second subtraction circuits are output by the logical operation output. Comb filter selected and taken out.