JPH0537591Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a dropout compensation circuit suitable for optical video disc players and the like.

(Prior art) A dropout compensation circuit that replaces a dropout with a line-correlated signal to make it less noticeable conventionally uses a delay device 1 of one horizontal scanning period (hereinafter referred to as 1H) as shown in FIG. 3A. Then, a color video signal to be applied to the input terminal of the delay device 1 is output.
When a dropout is detected, the output of the delay device 1 is made to be the input of the delay device 1.

Further, as shown in FIG. 3B, it is equipped with a delay device 1 that delays the luminance signal (Y input) for a period of 1H, and a delay device 2 that delays the color signal (color input) for a period of (1H-0.5C). A luminance signal and a chrominance signal, which are applied separately to the input terminals of devices 1 and 2, are added and output. When a dropout is detected, the output of delay device 1 is made to be the input of delay device 1, and the output of delay device 2 is made to be the input of delay device 2. Here, C indicates the color carrier wave period.

(Problem that the invention attempts to solve) However, since the chrominance signal uses a carrier wave with a frequency whose phase is inverted for each line and is frequency interleaved with the luminance signal, the former method of the conventional example described above is not applicable. At that time, there were problems that could not be compensated for.

In addition, in the former conventional example described above, it is possible to compensate for the chrominance signal by increasing or decreasing the delay time of the delay device 1 by 0.5C from 1H, but the phase of part of the luminance signal is There was a problem in that part of the image outline was distorted when the image was rotated.

Further, in the case of the latter of the above-mentioned conventional examples, compensation is good, but there is a problem that the number of parts increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a dropout compensation circuit that compensates for color signals, does not distort part of the image contour, and has a simple configuration.

(Means for achieving the purpose) A delay device that delays an input color video signal by a delay time that is shorter than one horizontal scanning period in the case of the NTSC system and two horizontal scanning periods in the case of the PAL system, and an output from the delay device is input,
The system further comprises a phase shifter which shifts the phase of an input by 0 to 180 degrees within a prescribed frequency range including the color carrier frequency, and switch means which receives an input color video signal as one input and uses the output of said phase shifter as the other input, and which, when a dropout is detected, directs the other input to the output and uses the output as the input of said delay device and as an output color video signal, so that the composite delay time characteristic of said delay device and phase shifter is one or two times the horizontal scanning period at low frequencies, and at the color carrier frequency is a delay time which is reduced from the delay time at said low frequency by approximately 1/2 the color carrier period.

(Function) The delay device and the phase shifter are connected in series, and when a dropout is detected, the output of the phase shifter is input to the delay device via the changeover switch means, and the dropout is compensated for using line correlation. be done.

However, since the combined delay time of the delay device and phase shifter is approximately 1H or 2H delay time at low frequencies, the main part of the spectrum of the luminance signal is distributed in the low frequency range of the color video signal. Therefore, the luminance signal in the high frequency range that is affected by the phase shifter is small, and the luminance signal is similar to that of the conventional dropout compensation circuit, and there is almost no image distortion.

Furthermore, since the synthesis delay time is set to be a delay time that is approximately 1/2 times the color carrier period less than the delay time at the low frequency at the color carrier frequency, no color shift occurs in the color signal.

As mentioned above, the present invention can also be said to match the phase by changing the synthesis delay time depending on the frequency.

(Example of idea) The present invention will be explained below with reference to examples.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The case of NTSC system is shown.

The color video signal is supplied to the delay device 12 through one contact of the changeover switch means 11 which is switched by the dropout detection output. The delay time of the delay device 12 is set to (1H-a), and the delay time of the delay device 12 is set to (1H-a).
Get the output from the input terminal of.

The delay device 12 is configured using, for example, a CCD, and the necessary low-pass filter is connected to the delay device 12.
It may be included in the output terminal, or it may be connected to the output terminal.

The output of the delay device 12 is applied to another contact of the changeover switch means 11 via a phase shifter 13.

FIG. 2 is a frequency characteristic diagram for explaining the operation of an embodiment of the present invention constructed as described above.

If dropout is detected and a dropout detection output is generated, the changeover switch means 11 switches from the state shown in FIG.
The output of the phase shifter 13 is supplied to the delay device 12, and the output of the phase shifter 13 is outputted as an output signal to compensate for dropout.

FIG. 2 is a frequency characteristic diagram for explaining the operation.

The delay time characteristic of the delay device 12 is as shown in FIG. 2A, and it delays the color video signal by (1H-a) time from the low frequency range. Frequencies above the band are indicated by broken lines. Note that c indicates the color carrier frequency.

The phase characteristics of the phase shifter 13 are as shown in FIG. 2B, and the amplitude characteristics are flat, but the phase characteristics rotate from near 0 degrees with frequency and approach 180 degrees.
Transistor 13 ₂ forming part of phase shifter 13
If the high-frequency attenuation characteristics are included, the phase will be more than 180 degrees, but that part is outside the usable band.

When this phase characteristic of the phase shifter 13 is multiplied by the color video signal period, the delay characteristic shown in FIG. 2C is obtained. That is, the delay characteristic decreases from a predetermined frequency lower than the color carrier frequency c and approaches "0". Semi-fixed resistor 13 forming part of phase shifter 13
When the resistance value of ₁ is changed, only the frequency in the range where the phase changes in Fig. 2B changes, but
In FIG. 2C, the delay amount a' in the flat portion and the frequency in the range where the delay amount changes change.

Here, the delay amount at color carrier frequency c is (a-
0.5C), the delay amount a of the deviation from (1H) of the delay device 12 is set to the delay amount a' of the flat portion in FIG. 2C.

Delay amount set in this way [1H−a (=a′)]
When the output of the delay device 12 is supplied to the phase shifter 13, the delay characteristic of the output from the phase shifter 13 is as shown in FIG. 2D. Therefore, the delay for the luminance signal is approximately (1H), the error is (a-a'), and there is little distortion of the image.
In addition, since the color signal has a delay of (1H-0.5C), no color shift occurs.

As a result, even during dropout compensation in which the changeover switch means 11 is switched by the dropout detection output and the output of the phase shifter 13 is applied to the delay device 12, image distortion is small and color shift does not occur.

In the case of PAL system, 2H may be used instead of 1H.

(Effects of the Invention) As described above, according to the present invention, both the luminance signal and the chrominance signal can be compensated for at the time of dropout with a simple configuration in which the output of the delay device is shifted by a phase shifter. The configuration for this purpose is also simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a frequency characteristic diagram for explaining the operation of an embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of a conventional example. 11... Selector switch means, 12... Delay device,
13... Phase shifter, 13 ₁ ... Semi-fixed resistor, 13 ₂ ...
...transistor.

Claims (1)

[Scope of utility model registration request] a delay device that delays the input color video signal by a predetermined time shorter than one horizontal scanning period in the case of the NTSC system and two horizontal scanning periods in the case of the PAL system; and an output from the delay device as input;
and a phase shifter that shifts the phase of the input by 0 to 180 degrees in a predetermined frequency range that spans the color carrier frequency, the input color video signal is used as one input, the output of the phase shifter is used as the other input, and dropout is detected. switch means for guiding the other input to the output when the phase shifter is input, and for making the output an input to the delay device and an output color video signal, and the composite delay time characteristic of the delay device and the phase shifter is low. The delay time is set to be 1 or 2 times the horizontal scanning period at the band frequency, and the delay time is reduced by approximately 1/2 the color carrier period from the delay time at the low band frequency at the color carrier frequency. A dropout compensation circuit characterized by: