JPH0370383A - Comb filter - Google Patents

Abstract

PURPOSE:To lead an excellent separation output out at all times without any influence of variation in the absolute level of an input signal upon discrimination making by discriminating the relative large/smell relation among input values and performing noncorrelative arithmetic. CONSTITUTION:Signals from absolute value circuits 13-16 are passed through low-pass filters(LPF) 31-34 respectively and suppled to the arithmetic part 35 which decides the relative large/small relation among the signal levels and performs the arithmetic. Then this arithmetic part 35 performs the specific arithmetic by regarding the outputs of the low-pass filters 31-34 as (x) and X, and (y) and Y. A switch 23 is controlled according to the arithmetic output. Thus, the arithmetic part 35 discriminates the relative large/small relation among the input values and performs the noncorrelative arithmetic, so the excellent separation output is led out at all times without any influence of the variation in the absolute level of the input signal upon the discrimination making.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a comb filter used for separating luminance signals and chroma signals in color TVs and VTRs.

[Summary of the invention]

The present invention relates to a comb filter, and when switching a plurality of filter outputs by determining non-correlation, by determining the relative magnitude relationship between data, it is possible to always use a comb filter, even when the input signal level is low. This makes it possible to obtain good separation output.

[Conventional technology]

For example, in the case of separating a luminance signal and a chroma signal in a color video signal of the NTSC system, a method of separation using a bandpass filter has been widely used. However, in this method, for example, 3.58MHz
Since all luminance signals included within the ±500kHz band are considered to be chroma signals, high-frequency components of the luminance signal are mixed into the chroma signal in areas where the luminance signal changes sharply, resulting in image deterioration called cross color. Occur.

In response, 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. Figure 2 shows the circuit, in which the signal from the input terminal (101) is supplied to the delay line (IHDL) (102) for one horizontal period, and the signal at the input and output terminals of this delay line (102) is sent to the subtraction circuit. (
103). This allows the subtraction circuit (1
03) A signal in which the luminance signal has been canceled is extracted from the filter, and this signal is passed through a band pass filter (B P F) (1
04), and the separated chroma signal is taken out to an output terminal (105). Also input terminal (101)
The signal from the subtractor circuit (107) is supplied to the subtractor circuit (107) through a delay line (DL) (106) corresponding to a signal delay such as a bandpass filter (104).
7) is supplied with the chroma signal from the bandpass filter (104), and the luminance signal from which the chroma signal has been removed is taken out to the output terminal (108).

[Problem to be solved by the invention]

However, in this case, for example, if a signal is supplied to the above-mentioned comb filter in which the luminance signal level is constant and the phase of the chroma signal is reversed (changed to complementary color) from an intermediate scanning line, then in this changed scanning line, Signal deterioration occurs due to the lack of vertical correlation in the chroma signal.In other words, the chroma signal remains on the changed scanning line in the luminance signal taken out to the output terminal (108), causing so-called dot interference. Furthermore, in the chroma signal taken out to the output terminal (105), the level of the chroma signal of the changed scanning line decreases, and the vertical resolution of the chroma signal deteriorates.

Alternatively, in scanning lines where the luminance signals have no vertical correlation, residual luminance signals may occur, and if this luminance signal includes band components near the chroma signal, cross color similar to the conventional technique may occur.

In response to this, the applicant of the present application previously proposed a comb filter that can perform separation without signal deterioration as described above by detecting vertical correlation (Japanese Patent Application No. 63-3017).
(See No. 62).

That is, in FIG. 3, a composite signal of the luminance signal "Y" and the chroma signal "C" from the input terminal (1) is transmitted to the first and second delay lines (IHDL) each having a delay time of one horizontal period. ) (2) and (3) are supplied to the series circuit. The signals at the input and output terminals of these delay lines (2) and (3) are transmitted to the first and second subtraction circuits (4) and (5), respectively.
supplied to

The signals at the input and output terminals of these subtraction circuits (4) and (5) are bandpass filters (B P F ) (6) (7) (8) that correspond approximately to the band of the chroma signal, respectively.
(9) Supplied to (10).

Output signals of filters (6), (8), and (10) among these are supplied to first and second adder circuits (11) and (12). The addition outputs of these adder circuits (11) and (12) and the output signals of filters (7) and (9) are absolute value circuits (ABS) (13), (14), and (15), respectively.
) (16) and a coring circuit that compares this absolute value with a predetermined potential and binarizes it (17) (18) (19) (
20) and is supplied to the logic operation unit (21).

On the other hand, signals ■ and ■ corresponding to the output chroma signals of the above-mentioned comb filter are extracted from the band pass filters (7) and (9), respectively, and the signal from the band pass filter (8) is further extracted from the conventional separation filter. A signal (2) corresponding to a conventional output chroma signal is extracted by being supplied to a band-pass filter (22) that forms a characteristic. Supplied.

Then, the coring circuit (1
Using the outputs of 7) to (20) as ■, ■, ■, and ■, respectively, logical operations are performed using the following truth table.

This calculation output is supplied to the switch (23), and the switch (23) is controlled according to the calculation output.

The signal from the switch (23) controlled by this is taken out to the chroma signal output terminal (24>).

Further, the signal from the output end of the delay line (2) is supplied to the subtraction circuit (26) through a delay line (D L) (25) corresponding to the signal delay of bandpass filters (7), (9), etc. The chroma signal from the switch (23) is supplied to the subtraction circuit (26), and the luminance signal from which the chroma signal has been removed is taken out to the output terminal (27).

Therefore, in this circuit, if a signal is supplied to the input terminal (1) in which the level of the luminance signal is constant and the phase of the chroma signal is reversed (changed to a complementary color) from an intermediate scanning line, the signals of each part will be The result will be as shown in Figure 4. Here, the waveform in the figure shows the phase of the chroma signal. Then, in the output a - C of the bandpass filter (6) (8) (10), if the phase is inverted at the position of the broken line, for example, originally l
The phases that should be inverted every horizontal period will continue to be in phase.

Note that c is each delayed by l horizontal period.

Further, these signals a-C are sent to the adder circuit (11), (1
2), a signal appears at the addition output on the scanning line whose phase is inverted, and the outputs (1) and (2) of the coring circuits (17) and (20) become "1".

On the other hand, the signals from the bandpass filters (7) and (9) ■.

In the case of (2), the subtraction output is missing due to a scanning line with an inverted phase, and in the past, dot interference etc. occurred when these signals were taken out. On the other hand, in the above-mentioned embodiment, the operation of the logic operation section (21) causes (■).

Since the signal (2) is taken out only when (2)=(0,'l), the ROMA signal "C" is taken out at the output terminal (24) as shown in the figure.

That is, this extracted chroma signal "C" is transmitted through the delay line (
By supplying these signals to the subtraction circuit (26), a luminance signal Y'' from which dot interference has been removed is taken out at the output terminal (27). Ru.

In addition, in a signal where the luminance signal level is constant and a chroma signal is added from an intermediate scanning line, the signals of each part are
As shown in the figure, when the signals ① and ② were conventionally extracted, the vertical resolution deteriorated. On the other hand, by making a selection using the signals ■ and ■, the ROMA signal "C" is extracted as shown in the figure.

On the other hand, if there is a luminance signal (the waveform is a luminance signal component near the chroma signal, and the phase of each scanning line is the same) only in two scanning lines in the middle, as shown in Figure 6, for example. In this case, the signals ■ and ■ become (1, 1). Here, the signals ■ and ■ are determined, and the signal ■ is taken out only when (■, ■) = (0, 1), so that the output terminal (24)
As shown in the figure, a chroma signal "C" from which the luminance signal component has been removed is extracted.

Furthermore, in this circuit, if a signal is supplied to the input terminal (1) in which the level of the luminance signal is constant and the chroma signal is present in only one scanning line in the middle, the signals of each part are The result will be as shown in the figure. Therefore, in this case, signal deterioration will occur no matter which of the signals (2) and (2) is selected.

On the other hand, in the circuit described above, the chroma signal separated by the usual method from the bandpass filter (8) is supplied to the third fixed contact of the switch (23>), while the signals ■, ■ , ■, and ■ all become "1", it is determined that there is no vertical correlation in both the luminance signal and the chroma signal, and during this period, by selecting the signal with the switch (23>), the output terminal ( 24), the chroma signal "C" without signal deterioration can be extracted as shown in the figure.

Therefore, according to this circuit, signals corresponding to the vertical correlation of the luminance signal and chroma signal are respectively taken out from the addition circuit and the subtraction circuit, and the comb filter output with the stronger correlation is selected, and both of the signals corresponding to the vertical correlation are selected. When the separation is poor, a good separated output can be obtained by selecting the output of the normal filter circuit.

Furthermore, in the circuit described above, the bandpass filter (7)
The signals from (9) and (9) are sent to the adder circuit (
This addition circuit (28) is supplied to the adder circuit (28).
), for example, a signal is taken out, and a signal (2) corresponding to the output of a so-called 2H comb filter based on the correlation of three scanning lines is taken out. This signal O is then supplied to the fourth fixed contact of the switch (23>).

On the other hand, the logic operation section (21) receives the same signal ■ as described above.

(2), (2), and (2) are supplied, and the logic operation section (21) performs a logical operation based on the following truth table, and the switch (23) is controlled according to the output of this operation.

The rest is the same as the circuit described above.

Therefore, in this circuit, the operations under each of the above conditions are performed in the same way, and, for example, when the level of the luminance signal is constant,
When a signal is supplied to the input terminal (1) in which the phase of the chroma signal is inverted (changed to a complementary color) in an oblique direction with an inclination of approximately half the wavelength of the color subcarrier every l scanning line, The signals of each part will be as shown in Figure 9, and the signal [stock] will be as shown in the figure.Then, when determining the signals ■, ■, ■, ■, this signal O is selected in the part where there is not much difference in correlation. As a result, a chroma signal "C" with no signal loss is extracted at the output terminal (24), and this signal is supplied to the subtraction circuit (26), thereby reducing dot interference in the luminance signal.

Note that the level of the chroma signal replaced by Signal Co., Ltd. is attenuated to about 172, but the effect of improving dot interference is 6 dB, and the effect of improving image quality is extremely large.

Therefore, according to this circuit, a signal corresponding to the output of a so-called 2H comb filter based on the correlation of the three scanning lines is extracted from the adder circuit (28), and when there is no difference in correlation, the output of this 2H comb filter is selected. By doing so, even better separation output can be obtained.

However, in the above circuit, the logic operation section (21)
The data supplied to the coring circuits (17) to (20
) is compared with a predetermined potential and binarized.

In this case, if the level of the input signal changes, there is a possibility that the effect of the above-mentioned comb filter cannot be obtained sufficiently.

That is, when the level of the input signal becomes small due to a weak electric field of the received signal, etc., the coring circuit no longer reaches the predetermined potential. In order to improve this problem, lowering the predetermined potential has resulted in problems such as increased sensitivity to noise.

In view of these points, this application provides a comb filter that can always obtain good effects even when the level of a human input signal changes.

[Means to solve the problem]

The present invention comprises delay lines (2), (3), subtraction circuits (4), (5) connected to the human output of this delay line, and filter circuits (6) to (5) connected to this subtraction circuit. 10)
and an adder circuit (11) connected to this filter circuit,
(12), a switching means (switch (23)) for switching the output of the filter circuit, and an arithmetic unit (35) for controlling this switching means, and this arithmetic unit calculates the relative magnitude relationship between input values. This is a comb filter that performs decorrelation calculations by determining the .

[Effect]

According to this, since the arithmetic unit determines the relative magnitude relationship between input values and performs non-correlation calculations, the determination is not affected by changes in the absolute level of the human input signal. , it is possible to always obtain good separation output.

〔Example〕

FIG. 1 shows the tank bottom of the example. In this figure, parts corresponding to the circuits shown in the above-mentioned prior art are given the same reference numerals and detailed explanations will be omitted.

In this figure, the signals from absolute value circuits (13) to (16>) are, for example, (1+2 Z-'+Z-''), and Z is passed through low-pass filters (LPF) (31) to (34) with sampling periods, respectively. The signal is supplied to an arithmetic unit (35) that determines the relative magnitude relationship of the signal levels and performs an arithmetic operation.Then, this arithmetic unit (35) uses low-pass filters (31) to <34
The calculations shown in the table below are performed using the outputs of
) is controlled.

Therefore, in this device, when y>2x, there is a lot of non-correlation on the y side, and the signal ■ is selected. Alternatively, when y<+x, there is a large amount of non-correlation on the X side, and signal (2) is selected, whereby good separated outputs are extracted. In contrast to this +
When y≦X≦2y and +Y≦X≦2Y, there is a chroma signal in only one scanning line, and in this case, L x , y ,
When the signal is present at a predetermined level or higher due to F O, X<2x, and Y<2y, the signal ■ is selected. Further, if none of the above is true, the correlation of the signals is at a predetermined level or higher, and the signal [stock] is selected.

In addition, in the above calculation formula, when the relative ratio of x, y or X, Y exceeds 2, the smaller value corresponds to the conventional "0" and the larger value corresponds to "1". .

In this way, according to the above-mentioned device, since the arithmetic unit determines the relative magnitude relationship between input values and performs non-correlation calculation, the determination is not affected by changes in the absolute level of the human input signal. This allows good separation output to be obtained at all times.

Note that in the above-mentioned apparatus, the actual signal waveform etc. are exactly the same as in the case of the apparatus described in the above-mentioned [Problem to be Solved by the Invention] section.

〔Effect of the invention〕

According to this invention, since the arithmetic unit determines the relative magnitude relationship between input values and performs non-correlation calculation, the determination is not affected by changes in the absolute level of the input signal. It is now possible to always obtain good separation output without any problems.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an example of the present invention, and FIGS. 2 to 9 are diagrams for explaining conventional techniques. (1) is an input terminal, (2) (3) (25) is a delay line, (4) (5) (26) is a subtraction circuit, (6) to (10)
(22) is a bandpass filter, (11) (12)
・ is an addition circuit, (13) to (16) are absolute value circuits, (2
3) is a switch, (24) and (27) are output terminals, (3)
1> to (34) are low-pass filters, and (35) is an arithmetic unit. Substitute Hide Hitomatsu Kuma 1st figure et al., et al., et al., et al. ♂-ra♂ ♂ra♂%-♂ 11011 1 1 1 101 Theory Sun Moon Figure 4 Figure 8-1 et al♂~Buff' -- 11-ra♂ et al♂- 1---ra♂ et al♂ rb t)＋c eζfu □□□(Meco □ □ □ □ ζ＼) □ □ □ ℃Meco001000
10 00010001 1-==Ra♂～-- 1--==♂Ra♂et al.00111110 0001 1 1 1 1 Explanatory diagram Figure 5-1Rara11111~μ~-11111~ ～- a+b b+c m-ranra m- 111raS~ra- 0011100 0001110 □□ri/ko □ qfu □ □ qfu □ (-)□ 001 01 00 0001010 Figure 8 1~---- 1 1~-1111 et al- a+b □ and Nfu CNfu □ □ b◆C qfu CN a □ 1100 0111 - ℃meko C□ko □ □ e□fu く〆co □ 1100 0 0 1 1 0 th Figure 7

Claims (1)

[Claims] A delay line, a subtraction circuit connected to the input/output of the delay line, a filter circuit connected to the subtraction circuit, an addition circuit connected to the filter circuit, and a subtraction circuit connected to the input/output of the delay line; A comb filter comprising a switching means for switching an output and a calculation section for controlling the switching means, and the calculation section performs a non-correlation calculation by determining a relative magnitude relationship between input values.