JPS61247193A - Comb line filter - Google Patents

Abstract

PURPOSE:To improve the color S/N and prevent the occurrence of color blur by outputting an input signal through a feedback comb line filter when vertical correlations of the color signal are great and outputting the input signal as it is when vertical correlations of the color signal are little. CONSTITUTION:An input signal 1 is inputted to the first synthesizer 2, the second syntherizer 4, and the third synthesizer 7, and the output of the first synthesizer 2 is inputted to a delay circuit 3, and the output of the delay circuit 3 is inputted to the second synthesizer 4, and the output of the second synthesizer 4 is inputted to a limiter circuit 5, and the output of the limiter circuit 5 is multiplied by a coefficient K, and the result is inputted to the first synthesizer 2. Simultaneously, the output of the limiter circuit 5 is multiplied by a coefficient 1+K/2, and the result is inputted to the third synthesizer 7, and the output of the third synthesizer 7 is outputted. Thus, the feedback comb line filter is constituted to increase the S/N improving effect when vertical correlations of the input color signal are great, and input color signals are outputted as they are when vertical correlations are little, thereby reducing considerably color blur in the vertical direction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a comb filter used in color signal processing circuits of VTRs and the like.

Conventional technology In recent years, feedback comb filters have been used for VTR color signal processing.
It's starting to be used.

First, let's look at a typical example of a conventional feedback comb filter.
As shown in the figure.

The input carrier color signal Cin reproduced from VT and R is supplied to a combiner 12 from an input terminal 11. The signal C4 from the combiner 12 is sent to the combiner 16, the combiner 16, and the 1H delay line 13 (
H is supplied in horizontal period).

In the combiner 16, from the signal C1 of the combiner 12, 1H
The signal Cd from the delay line 13 is subtracted and the output color signal Cou
t is output to the output terminal 17.

Also, in the synthesizer 16, the signal Cd from the 1H delay line 13
and the signal C4 from the combiner 12 to obtain a sum signal C.
2 is obtained, and this sum signal C2 is supplied through a feedback circuit 14 to a synthesizer 12 at the input stage of the comb filter.

FIG. 7 shows a frequency characteristic curve of the feedback comb filter constructed in this manner. When the amount of feedback is 0, a curve of a normal comb filter is shown as shown by curve a, and when the amount of feedback is large, a curve of a feedback type comb filter is shown as shown by curve C. If the amount of feedback is adjusted, a characteristic between curve a and curve C (for example, curve b) will be exhibited.

In the case of curve C, the chroma S/N improvement effect is large, but
There is a drawback that color shift and color blurring of the outline of the color image becomes large. Conventionally, as a method of correcting this defect, the strong correlation between the luminance signal and the chroma signal has been utilized to detect the vertical correlation of the luminance signal, and the amount of feedback of the chroma signal has been controlled based on this information. This block diagram is shown at 21 in FIG. That is, the reproduced luminance signal Y input to the input terminal 10 is passed through the 1H delay line 18 to obtain the delayed signal Yd.
The synthesizer 19 detects the difference between d and signal Y to detect the vertical correlation of the luminance signal. Then, the output Y of the synthesizer 19
When the absolute value level of , increases, the amount of feedback is reduced in the feedback circuit 14 to reduce color blurring, and when the absolute value level decreases, the amount of feedback is increased to improve the chroma S/N.

As another configuration, as shown in Fig. 8, by inserting a limiter circuit into the feedback loop, when the vertical correlation of color signals is large, the amount of feedback is increased to improve the S/N, and the vertical When the correlation is small, the color blurring can be reduced by reducing the amount of feedback, as proposed by the inventor in Japanese Patent Application No. 59-176.
This is proposed in No. 93. A detailed explanation of the operation of each part will be omitted here.

Problems to be Solved by the Invention However, in the above configuration, even when there is no vertical correlation of color signals, the configuration is similar to that of a normal comb filter, so color blurring occurs in principle during the 1H period. There was a problem that this occurred.

In view of the above problems, the present invention provides a feedback comb filter which, in principle, hardly causes color fringing when there is no vertical correlation of color signals.

Means for Solving the Problems In order to solve the above problems, the comb filter of the present invention has the following features: Second. The third synthesizer includes a delay circuit and a limiter circuit, and inputs the input signal to the first... Second. the output of the first combiner is input to the delay circuit, the output of the delay circuit is input to the second combiner, and the output of the second combiner is input to the second combiner; input to the limiter circuit, multiply the output of the limiter circuit by a coefficient of 1 and input it to the first combiner, and at the same time multiply the output of the limiter circuit by a coefficient of 2 and input it to the third combiner. death,
It is configured to output the output of the third synthesizer (K2-(K,+1)/2).

Effect of the Invention With the above-described configuration, the present invention uses a feedback comb filter to improve color S when the vertical correlation of color signals is large, and uses the input signal as is when the vertical correlation of color signals is small. By outputting, it is possible in principle to prevent color bleeding from occurring.

EXAMPLE Hereinafter, a comb filter according to an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the invention. In Figure 1, 1 is an input terminal, 2°4.7 is a 1st, 2, and 3rd combiner, 3 is a 1H delay circuit, 5 is a limiter circuit, and 6 and 8 are coefficient circuits that indicate signal coefficients. Reeds and 9 are output terminals.

The signal input through input terminal 1 is sent to combiner 2°4.7. The output of the synthesizer 2 is passed through the 1H delay circuit 3,
After being delayed by H, it is sent to the combiner 4. The output of combiner 4 is sent to limiter circuit 6.

The signal whose amplitude has been limited by the limiter circuit 6 is sent to the synthesizer 2 through a coefficient circuit 8 having a feedback amount K, and at the same time is sent through the coefficient circuit 6 to a synthesizer 7 where it is combined with the input signal and then output terminal. Regarding the comb-shaped filter configured as 0 or more, which is output to the cylinder 9, the following cylinder 1. Second. The operation will be explained using FIG.

First, consider a case where the vertical correlation of color signals is large.

At this time, the output of the synthesizer 4 is only a small signal component and is not affected by the limiter circuit 5 at all. The transfer function G of the comb filter at this time is expressed as G=(1-Z)(1-K)/(2x(1+KZ)) where Z=jwt.

The frequency characteristics at the right time change depending on the feedback amount K, as shown in FIG.

When K=o, the second
In Figure a), the improvement effect of S in this case is about 3 dB. K
When K=0.5 (FIG. 2b), the S/N improvement effect is about edB, and when K=0.8 (FIG. 2C), the S/N improvement effect is about 1 odB.

In other words, the S/N improvement effect of the conventional comb filter is 3.
dB, for example, if = 0.8, it is 10 dB,
This is a significant improvement. Further, in this case, since the vertical correlation is large, color bleeding in the vertical direction is not noticeable at all.

Next, consider a case where the vertical correlation of color signals is very small.

At this time, the output of the synthesizer 4 becomes large and most of the components are limited by the limiter circuit 6, so that almost no signal is sent to the synthesizer 7. At this time, the transfer function G of the comb filter becomes G#1, the input signal is output as is, and color blur in the vertical direction does not occur.

The present invention can also be explained as follows.

FIG. 3 shows the frequency characteristics of the comb filter according to the present invention, taking into account the input signal level.

In other words, at a small signal level where there is a lot of noise, the S/N is reduced by the effect of the feedback comb filter as shown in Figure 3d.
Although there is some vertical color bleeding, it is hardly noticeable due to the small signal.

It can be seen that at a large signal level with a good S/N ratio, as shown in FIG. 3a, there is no improvement in S, but no vertical color blurring occurs.

In the embodiment described above, as shown in FIG.
Although it is also possible to return the color to 1, the amount of improvement in color fading is greater with the configuration shown in this embodiment. The reason for this will be briefly explained below.

When the output signal of the combiner 4 is fed back to the combiner 2 without passing through the limiter circuit 6, the transfer function G1 up to the stage before the limiter circuit is G1-(1+Z)/( 1+KZ) It can be seen that the feedback loop is always operating.

On the other hand, when the output signal of the synthesizer 4 is fed back to the synthesizer 2 after passing through the limiter circuit 6 as shown in this embodiment, the transfer function G1 when there is vertical correlation of color signals is as follows: G1=(1+Z )/(1+KZ), which is the same as the above example, but if there is no vertical correlation between the color signals, the feedback signal is limited, so it becomes K#0, and the transfer function G1 at that time is simply expressed as G1 gradient 1+Z. It is similar to a comb-shaped filter. Finally, if there is no vertical correlation between color signals, the feedback loop will not operate.

Here, when there is no vertical correlation of color signals, the limiter circuit 6
The minute signal that is not limited by the input signal is combined with the input signal in the synthesizer 7 and then output, which may cause slight color distortion.
It is preferable that there be no such slight color deviation, that is, when there is no vertical correlation of the color signals, it is preferable that the feedback loop does not operate.

That is, it is better to feed the output signal of the synthesizer 4 back to the synthesizer 2 after passing it through the limiter circuit 6 as shown in this embodiment. This is considered more desirable than having them return to Japan.

Furthermore, a limiter circuit may be inserted in the system that feeds back the output signal of the combiner 4 to the combiner 2 and the system that sends it to the combiner 7 (see Figure 6), but in that case, the limiter circuit is A circuit is required. According to the present invention, only one limiter circuit is required, resulting in an extremely simple configuration compared to a configuration with two circuits, and this has great effects.

In the above-described embodiment, the coefficient of the coefficient circuit 8 indicating the amount of feedback can be arbitrarily selected, but preferably 0.6 to 0.8. Further, the limiter level of the limiter circuit 6 can be arbitrarily selected, but it is preferably about 1 to 30 degrees of the maximum amplitude of the output of the synthesizer 4. In addition, the record sickle playback mode (VH3-VTR
In this case, the value of K and the limiter level may be switched between the 2-hour mode and the 6-hour mode.

Further, the present invention can improve not only the S/N of color signals but also the S/N of luminance signals with a similar configuration. However, the transfer function shown in the embodiment takes into consideration that the phase of the color signal becomes opposite every 1H. ! It is necessary to change the name of the temple where the historical site is located.

Effects of the Invention As described above, the present invention allows input signals to be input to the first . 2nd, 3rd
the output of the first combiner is input to the delay circuit, the output of the delay circuit is input to the second combiner, the output of the second combiner is input to the limiter circuit, and the output of the first combiner is input to the limiter circuit. The output of the circuit is multiplied by a coefficient and input to the first combiner, and at the same time, the output of the limiter circuit is multiplied by a coefficient by 2 and input to the third combiner, and the output of the third combiner is output. By configuring it as follows, when the vertical correlation of the input chrominance signal is large, a feedback comb filter is configured to increase the S/N improvement effect, and when the vertical correlation is small, the input chrominance signal is Vertical color bleeding can be significantly reduced even if the image is output almost as is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a comb filter in one embodiment of the present invention, FIGS. 2 and 3 are its frequency characteristics diagrams, FIGS. 4 and 6 are configuration diagrams of other embodiments, and FIG. , FIG. 8 is a block diagram of the conventional example, and FIG. 7 is its frequency characteristic diagram. 2.4.7...Synthesizer, 3...River delay circuit,
6...Limiter circuit, 6, 8...Coefficient circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 6 Figure 7 h

Claims (4)

[Claims] (1) It comprises first, second, and third combiners, a delay circuit, and a limiter circuit, and the input signal is transmitted to the first, second, and third combiners.
the output of the first combiner is input to the delay circuit, the output of the delay circuit is input to the second combiner, and the output of the second combiner is input to the limiter. The output of the limiter circuit is multiplied by a coefficient K_1 and inputted to the first combiner, and at the same time, the output of the limiter circuit is multiplied by a coefficient K_2 and inputted to the third combiner. A comb filter characterized in that it is configured to output the output of the synthesizer of No. 3. (2) Between coefficient K_1 and coefficient K_2, K_2=(1
The comb filter according to claim 1, wherein the comb filter is configured to have a relationship of +K_1)/2. (3) The comb filter according to claim 1, wherein the first synthesizer and the third synthesizer are subtracters. (4) The comb filter according to claim 1, wherein the delay circuit is configured to delay by one horizontal period.