JPH04309091A - Picture signal reproduction device - Google Patents

Abstract

PURPOSE:To make it less easily recognizable even when lots of dropout take place by adding a color signal to a signal to be replaced at dropout. CONSTITUTION:The device is provided with an input terminal 11, 1st-5th delay circuits 12, 19, 15, 25, 26, a 2-multiple amplifier 13, 1st and 2nd adders 14, 16, 1st and 2nd circuits 17, 18, a subtractor 18, a switch 21, a dropout detection circuit 22, an output terminal 23 and a 1/2 multiple amplifier 24. Then a composite video signal is inputted from the input terminal 11 to the switch 21 and the switch 21 is thrown to the position (b) on the occurrence of dropout to input an output of the subtractor 18 to the 1st delay circuit 12 giving a shorter delay by a sum time between a 1/2 period time of a chrominance subcarrier of a composite video signal and a preset time from one horizontal scanning time of the inputted composite video signal. Thus, a replacement signal with a color signal is inputted to the 1st delay circuit 12 even on the occurrence of dropout. Thus, the composite video signal replaced with the replacement signal with the color signal is obtained from the output terminal 23.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compensation for signal loss such as dropout in a video signal reproducing device such as a video display player.

0002

2. Description of the Related Art In recent years, video signal reproducing devices such as video disc players and video recorders have become widespread. Video signals extracted from recording media such as video disks and magnetic tapes often contain defects (dropouts) that cause disturbances when reproduced as images on a television receiver. In the future, there will be a need for a video signal reproducing apparatus that is equipped with an effective compensation system for missing reproduction signals due to dropouts or the like.

The operating principle of dropout compensation in a conventional video signal reproducing device focuses on the correlation of video signals. In other words, the information on a certain scanning line on the TV screen is similar to the information on the previous scanning line, so if a dropout occurs in the video signal due to a dropout, etc. The loss can be compensated for by outputting information from the previous scan line instead.

An example of the above-mentioned conventional video signal reproducing apparatus will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of a conventional video signal reproducing device. In the figure, 1 is an input terminal, 2 is a delay circuit, 3 is a low-pass filter, 4 is a switch, 5 is a dropout detection circuit, and 6 is an output terminal.

The operation of the conventional video signal reproducing apparatus configured as described above will be explained below.

In FIG. 3, a composite video signal is input to an input terminal 1. The input composite video signal is sent to switch 4.
is input. The dropout detection circuit 5 normally operates (
(if there are no dropouts in the input composite video signal),
Set switch 4 to terminal a, and in case of abnormality (when there is a dropout in the input composite video signal) switch 4 to terminal b.
Set to terminal. The output of the switch 4 is input to the delay circuit 2, and the composite video signal delayed by the delay circuit 2 is input to the low-pass filter 3. The delay circuit 2 delays the input signal by exactly one horizontal scanning time and outputs the delayed signal. Therefore, the composite video signal input to the low-pass filter 3 becomes a signal exactly one horizontal scan earlier than the signal input to the delay circuit 2. Only the high frequency components of the composite video signal input to the low pass filter 3 are attenuated by the low pass filter 3, and only the low frequency components are input to the b terminal of the switch 4. In the composite video signal, most of the luminance signal components are included in a low frequency, and the color signal components are included in a frequency band near a relatively high frequency color subcarrier. As shown in FIG. 4, the attenuation characteristic of the low-pass filter 3 is designed to block the color signal component, so that only the luminance signal component of the output of the delay circuit 2 can be input to the b terminal of the switch 4. can. Therefore, if there is no dropout in the input composite video signal, the input composite video signal is output as is to the output terminal 6, and if there is a dropout in the input composite video signal, the luminance signal from one horizontal scanning time ago is replaced. and output.

The reason why the replacement signal is performed using only the luminance signal is that in a composite video signal, the phase of the color signal component is inverted every horizontal scan, so the signal including the color signal is replaced with the signal from one horizontal scan time ago. This is because the colors will not be reproduced correctly.

That is, in a composite video signal, even if a color signal is reproduced as a luminance signal in a black and white receiver, the relationship between the horizontal scanning frequency and the color subcarrier frequency is set to an odd /2) (45 in NTSC system)
5/2). Therefore, the color subcarrier signals have a 180° phase difference between adjacent scan lines in the same field. Therefore, if a dropout occurs and a part of the previous line is replaced, it will appear as an inappropriate color.

0010

[Problems to be Solved by the Invention] However, in a video signal reproducing device having such a configuration, the signal replaced at the time of dropout is only a luminance signal, and when there is little dropout, the replaced signal is , which was effective because it was hard to notice, but when there were many dropouts, there were many areas on the screen where there was no color signal, which caused the problem that it was easy to stand out.

The present invention solves the above-mentioned conventional problems, and provides a video signal reproducing device that adds a color signal to the signal replaced at the time of dropout, and is less noticeable even when there are many dropouts. With the goal.

0012

[Means for Solving the Problems] The present invention provides a method that is shorter than one horizontal scanning time of an input composite video signal by the sum of 1/2 cycle time of the color subcarrier of the composite video signal and a preset time. a first delay means for applying a delay; an amplification means for doubling the output value of the first delay means; and a second delay means for delaying the output of the first delay means by a half cycle time of the color subcarrier of the composite video signal. a first adder for adding the output of the amplification means and the output of the second delay means; and a first adder for delaying the output of the first adder by a half cycle time of the color subcarrier of the composite video signal. a second adder that adds the output of the first delay means and the output of the third delay means; and a delay of a preset time by multiplying the output value of the second adder by 1/2. an arithmetic unit that subtracts a signal delayed by a preset time to the output of the second delay means from a signal given a predetermined time delay; and a detection means that detects signal loss in the input composite video signal and generates a control signal;
A switch means is provided for selecting the input composite video signal and the arithmetic unit output in response to a control signal and inputting the selected signal to the first delay means.

[0013]

[Operation] With this configuration, the signal to be replaced at the time of dropout is a signal in which the phase of the color signal of the signal one horizontal scanning time before the input composite video signal is inverted, and the color signal is replaced at the time of dropout. In addition, it is possible to provide a video signal reproducing device that is hardly noticeable even when there are many dropouts.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The operating principle of dropout compensation of the video signal reproducing apparatus according to an embodiment of the present invention focuses on the correlation of video signals. In other words, the information on a certain scanning line on the TV screen is similar to the information on the previous scanning line, so if a dropout occurs in the video signal due to a dropout, etc., the information on one scanning line before the dropout position is approximate. By outputting information from the scanning line instead, the loss can be compensated for.

In FIG. 1, 11 is an input terminal, 12 is a first delay circuit, 13 is a double amplifier, 14 is a first adder, 15 is a third delay circuit, 16 is a second adder, 17 is a first circuit, 18 is a subtracter, 19 is a second delay circuit, 2
0 is a second circuit, 21 is a switch, 22 is a dropout detection circuit, 23 is an output terminal, 24 is a 1/2 amplifier,
25 is a fourth delay circuit, and 26 is a fifth delay circuit.

The operation of the video signal reproducing apparatus configured as described above will be explained below. First, a composite video signal is input from the input terminal 11 to the switch 21 . The dropout detection circuit 22 sets the switch 21 to the a terminal when there is no dropout in the input video signal,
The composite video signal input to the input terminal 11 is input to the first delay circuit 12 . The first delay circuit 12 delays the input signal by approximately one horizontal scanning time and outputs the signal. The composite video signal that has passed through the first delay circuit 12 is amplified twice by the double amplifier 13 and then input to the a input terminal of the first adder 14 . Moreover, the output of the first delay circuit 12 is
In the second delay circuit 19, one of the color subcarriers of the composite video signal is
It is given a delay of /2 period time and is input to the input terminal b of the first adder 14. The first adder 14 performs a+b calculation and outputs the result to the output terminal c. The output of the first adder 14 is given a delay of 1/2 period of the color subcarrier of the composite video signal by the third delay circuit 15, and is input to the input a terminal of the second adder 16. be done. Also,
The output of the first delay circuit 12 is input to the input terminal b of the second adder 16. The second adder 16 performs the a+b calculation and outputs the result to the output terminal c. The output of the second adder 16 is input to the first circuit 17. Further, the output of the second delay circuit 19 is input to the second circuit 20. The first circuit 17 includes a 1/2 amplifier 24 and a fourth delay circuit 25, and the signal input thereto is multiplied by 1/2, delayed for a certain period of time, and output. second circuit 20
consists of a fifth delay circuit 26 which gives the input the same amount of delay time as the fourth delay circuit 25, and the signal input here is output after being delayed by a certain period of time. first circuit 1
7 is input to the input terminal a of the subtracter 18, and the second
The output of the circuit 20 is input to the input terminal b of the subtracter 18. The subtracter 18 performs a-b calculation and outputs the result to the output terminal c. The output of the subtracter 18 is input to the b terminal of the switch 21. When there is a dropout in the input video signal, the dropout detection circuit 22 sets the switch 21 to the b terminal and inputs the output of the subtracter 18 to the first delay circuit 12. A double amplifier 13, a first adder 14, a third delay circuit 15, a second adder 16, a first circuit 17, a subtracter 18, a second delay circuit 19, The second circuit 20 constitutes a filter, and rotates the phase of the color signal by 180 degrees from the output signal of the first delay circuit 12 with respect to the signal one horizontal scanning time before the input of the first delay circuit 12. It functions to generate a signal and output it to the output of the subtracter 18.

Next, how can the phase of the color signal be 18?
How a replacement signal rotated by 0 degrees is generated will be explained using a transfer function.

The delay element is a delay element, and it is assumed that the delay element is sampled at four times as many clocks as the color subcarrier of the input video signal.

When the sampling time is t, the transfer function of the delay element due to one clock delay is Z-1=e-jwt :W=2πf
f can be expressed as the input signal frequency. Therefore, the transfer function from the output of the first delay circuit 12 to the output of the first adder 14 is 2+Z-2, and the transfer function from the output of the first delay circuit 12 to the output of the second adder 14 is 2+Z-2. Adder 1
The transfer function from the output of the first delay circuit 12 to the output of the subtracter 18 is (2+Z-2)*Z-2+1=Z-4+2Z-2+1, and the transfer product from the output of the first delay circuit 12 to the output of the subtracter 18 is The delay time of the delay circuit 17 is 1
If t (=1/4 color subcarrier period time), the delay time of the fifth delay circuit 26 is also 1t, so 0.5(Z-
4+2Z-2+1)Z-t-Z-2Z-t:t=1
becomes. Furthermore, the transfer function from the output of the first delay circuit 12 to the output of the second circuit 26 is Z-2Z-t:t=1, so the transfer function from the output of the second circuit 26 to the subtracter 18 is:

[0021]

[Math 1]

[0022] If we graph this transfer function, we get
As shown in FIG. 2, it can be seen that the phase around the color signal band is rotated by 180 degrees. That is, with respect to the output of the second delay circuit 19, the phase of the output of the subtracter 18 around the color signal band is rotated by 180 degrees.

Now, from the input of the first delay circuit 12 to the second
If the delay time to the output of the circuit 20 is set to be exactly one horizontal scanning time of the input video signal, the output of the subtracter 18 will be such that the phase around the color signal band of the signal just 1H before the video input signal is The signal will be rotated 180 degrees. Therefore, by switching the output of the subtracter 18 using the switch 21 and inputting it to the first delay circuit 12 when a dropout occurs, a replacement signal with a color signal can be input to the first delay circuit 12 even when a dropout occurs. can.

[0024] Therefore, at the output terminal 23, a composite video signal is obtained which is replaced by a replacement signal to which a color signal is added at the time of dropout.

As is clear from FIG. 2, the replacement signal at the time of dropout has a small gain near half the frequency of the chrominance signal, but this signal deterioration is not a problem in practice, and rather the replacement signal A color signal is added to
This is effective for making dropouts less noticeable.

As described above, according to this embodiment, the input terminal, the first delay circuit, the double amplifier, the first adder, the third delay circuit, and the second adder , a first circuit;
A subtracter, a second delay circuit, a second circuit, a switch, a dropout detection circuit, and an output terminal are provided, and the first circuit has a 1/2 amplifier and a fourth delay circuit. The second circuit is configured with the fifth delay circuit 26, so that the signal to be replaced at the time of dropout is a signal obtained by inverting the phase of the color signal of the signal one horizontal scanning time before the input composite video signal. It is possible to provide a video signal reproducing device that is not conspicuous even when there are many dropouts by adding a color signal to the signal that is replaced at the time of dropouts.

In one embodiment of the present invention, the output terminal 23 is connected to the output of the fifth delay circuit; The output of the delay circuit 19 may be used, and the present invention only changes the delay time from input to the input terminal 11 until the signal appears at the output terminal, and a delayed signal with a color signal is obtained at dropout. The effect of one embodiment remains the same.

When this embodiment is implemented using a digital integrated circuit or the like, the first delay circuit 12 and the second delay circuit 1
9, a third delay circuit 15, a fourth delay circuit 25,
The fifth delay circuit 26 can be configured with a latch,
The 2x amplifier 13 and the 1/2x amplifier 24 can be realized by bit shifting.

In one embodiment of the present invention, the delay time of the fourth delay circuit 25 and the fifth delay circuit 26 is set to 1t.
However, as is clear from the above calculation of the transfer function, any number may be used as long as they are equal to each other. Generally, when implementing the present invention in a digital integrated circuit, unless a delay circuit (latch) is inserted after the adder, etc., the delays of each bit signal will not be aligned, which may be inconvenient for circuit implementation. . Assuming such a case, in this example, the delay of 1t is reduced to 1/
Although it is inserted after the double amplifier 24, if this is unnecessary due to the characteristics of the integrated circuit, this delay can be eliminated, and at the same time, the delay time of the fifth delay circuit 26 can be set to 0 in order to match the delay time.

[0030]

[Effects of the Invention] From the above explanation, it is clear that the present invention is shorter than one horizontal scanning time of the input composite video signal by the sum of 1/2 cycle time of the color subcarrier of the composite video signal and a preset time. a first delay means for applying a delay; an amplification means for doubling the output value of the first delay means; and a second delay means for delaying the output of the first delay means by a half cycle time of the color subcarrier of the composite video signal. a first adder for adding the output of the amplification means and the output of the second delay means; and a first adder for delaying the output of the first adder by a half cycle time of the color subcarrier of the composite video signal. a second adder that adds the output of the first delay means and the output of the third delay means; and a delay of a preset time by multiplying the output value of the second adder by 1/2. an arithmetic unit that subtracts a signal delayed by a preset time to the output of the second delay means from a signal given a predetermined time delay; and a detection means that detects signal loss in the input composite video signal and generates a control signal;
By providing a switch means for selecting the input composite video signal and the arithmetic unit output in response to the control signal and inputting the selected input composite video signal to the first delay means, the signal to be replaced at the time of dropout can be replaced by one horizontal signal of the input composite video signal. This is done using a signal with the phase of the color signal of the signal before the scanning time inverted, and the color signal is also added to the signal that is replaced at the time of dropout, making it possible to realize a video signal reproducing device that is less noticeable even when there are many dropouts. It is.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a video signal reproducing device in an embodiment of the present invention.

[Fig. 2] Characteristic diagram of a filter in one embodiment of the present invention

[
Figure 3: Block diagram showing a conventional video signal reproducing device

[Figure 4
]Characteristic diagram showing the characteristics of a filter in a conventional video signal reproducing device

[Explanation of symbols]

11 Input terminal 12 First delay circuit 13 2x amplifier 14 First adder 15 Third delay circuit 16 Second adder 17 First circuit 18 Subtractor 19 Second delay circuit 20 Second circuit 21 Switch 22 Dropout detection circuit 23 Output terminal 24 1/2 times amplifier 25 Fourth delay circuit 26 Fifth delay circuit

Claims (3)

[Claims] 1. A first delay that provides a delay shorter than one horizontal scanning time of the input composite video signal by a time equal to the sum of 1/2 cycle time of the color subcarrier of the composite video signal and a preset time. means, an amplifying means for doubling the output value of the first delaying means, and a second delaying means for delaying the output of the first delaying means by a half cycle time of a color subcarrier of the composite video signal. , a first adder for adding the output of the amplification means and the output of the second delay means, and a first adder for delaying the output of the first adder by a half cycle time of the color subcarrier of the composite video signal. a second adder for adding the output of the first delay means and the output of the third delay means; and a second adder for adding the output of the first delay means and the output of the third delay means; an arithmetic unit that subtracts the signal delayed by the preset time from the output of the second delay means from the signal delayed by the predetermined time; and an arithmetic unit that detects signal loss in the input composite video signal and outputs a control signal. a detection means for generating a video signal; and a switch means for selecting the input composite video means and the output of the arithmetic unit in response to the control signal and inputting the selected result to the first delay means. playback device. 2. The video signal reproducing device according to claim 1, wherein the preset time is a quarter cycle time of a color subcarrier of the composite video signal. 3. The video signal reproducing apparatus according to claim 1, wherein the preset time is 0.