JPS60128789A - Correction circuit of dropout - Google Patents

Abstract

PURPOSE:To prevent dropout from affecting its picture quality by a means for switching the 1st synchronizing signal of a luminance signal to the 2nd one and a means for synthesizing a color difference signal and a luminance signal through said means and for forming a reproduction video signal. CONSTITUTION:In response to a dropout detection signal, a switching circuit 12 selects and switches the 1st reproduction video signal to the 2nd one which delays the 1st one by one horizontal scanning period, and vice versa. A synchronizing signal forming means 14b of a synchronizing signal processing means 14 forms the 2nd synchronizing sgnals H2 and V2 in synchronization with the 1st synchronizing signals H1 and V1. A synchronizing signal switching means 14c replaces said signals H1 and V1 with H2 and V2. A synthesizing means 16 synthesizes a color difference signal (c) from a color difference signal processing means 15 and said luminance signal Y, which is outputted. Thus dropout generated in an input signal is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a so-called video signal reproducing device such as a video disc player, a video tape recorder, etc. That is, the present invention relates to a dropout correction circuit that corrects dropout.

(Prior Art) A so-called video signal reproducing device such as a video disc player or a video tape recorder reads and reproduces a recorded signal on a video signal recording medium such as a video disc. In this reproduced signal, that is, the reproduced video signal,
These include video signals, horizontal synchronization signals, vertical synchronization signals, equivalent pulses, etc., and dropouts may occur when these signals are read from the recording medium by the video signal playback device. When a playback video signal in which dropout has occurred is applied to the video signal terminal of a CRT,
Black or white dots appear on the display screens of the C and RT, which impairs the image quality of the display screens. In order to prevent this, a conventional video signal reproducing apparatus is provided with a dropout correction circuit shown in FIG. 1 to correct this dropout. That is, in FIG.
2 is a dropout correction circuit for the reproduced video signal output from the video signal demodulation section 1, and 3 is a comb filter as a delay separation means (not shown). It is. The dropout correction circuit 2 includes a dropout detection circuit 4 that detects dropout of the reproduced video signal from the video signal demodulator 1, a delay circuit 5 that delays the reproduced video signal by one horizontal scanning period, and a dropout detection circuit. 4 in response to the dropout detection signal from the first
It includes a switching circuit 6 that selectively switches and outputs a reproduced video signal and a second reproduced video signal delayed by one horizontal scanning period. The comb filter 3 includes a delay circuit 5 shared with the dropout correction circuit 2, an addition circuit 3a, and a subtraction circuit 3b.

Normally, the first reproduced video signal output from the video signal demodulator 1 is supplied to the next stage comb filter 3 via the switching circuit 6 of the dropout correction circuit 2. On the other hand, when a dropout occurs in the first reproduced video signal that is the output of the video signal demodulation section 1, the dropout is detected by the dropout detection circuit 4, and as a result, the dropout detection circuit 4 detects the dropout detection signal. It is outputted and given to the switching circuit 6.

In response to this dropout detection signal, the switching circuit 6 outputs a second reproduced video signal delayed by one horizontal scanning period of the delay circuit 5. Therefore, the second playback video signal with no dropout outputted one horizontal scanning period ago via the switching circuit 6 is returned to the switching circuit 6.
This second reproduced video signal that has been returned is output from the switching circuit 6 again. In other words, when a dropout occurs in the first playback video signal output from the video signal demodulation section 1, the switching circuit 6 always outputs the second playback video signal with the dropout corrected.
The signal is applied to the CRT via the comb filter 3 in the next stage. However, when dropout occurs at the start of the vertical synchronization signal period of the first reproduced video signal from the video signal demodulator 1, the following problems occur. This content will be explained using FIG. 2. FIG. 2 is a timing chart of vertical synchronization signals, horizontal synchronization signals, etc. In FIG. 2, 1 H is 1 of the first reproduced video signal.
The horizontal scanning period is shown, and (a) is at the start of the vertical synchronization signal (
This is the first reproduced video signal in which dropout occurred at time H). At time t1, the dropout detection signal shown in FIG. 2(b) is applied from the dropout detection circuit 4 to the switching circuit 6, so at this time t1, the switching circuit 6 converts the output signal into the first reproduced video signal. The vertical synchronization signal is switched to the second reproduction video signal of one horizontal scanning period 1H earlier. In this case, switch to equivalent pulses.

Therefore, in the second reproduced video signal output from the switching circuit 6, a part of the vertical synchronization signal is lost as shown in FIG. 2(c), and the vertical synchronization signal period is from time t1 to
t2 is shorter than in the normal case, resulting in a signal in which the required vertical scanning period is not secured.

For this reason, when such a second playback video signal is applied to a CRT, a problem arises in that the display screen of the CRT shakes in the vertical direction. It was not enough to keep it in good condition.

(Purpose) The present invention is to ensure that even if dropout occurs in the vertical synchronization signal portion of a reproduced video signal, it will not directly affect the image quality of a CRT display screen, thereby ensuring good image quality at all times. With the goal.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings. FIG. 3 is a dropout correction circuit diagram according to an embodiment of the present invention. Although this embodiment will be described as being applied to, for example, a video disc, it is not limited thereto, and can similarly be applied to a video tape recorder or other recording/reproducing apparatus. In FIG. 3, reference numeral 10 denotes a video signal demodulation unit that reads a recorded signal from a video disk (not shown) input from an input terminal IN and performs 1) FM demodulation, and 11 a first reproduced video signal from the video signal demodulation unit 10. 12 is a dropout detection circuit 1 for detecting dropout of
Individual contacts for selectively switching and outputting the first reproduced video f signal and the second reproduced video signal obtained by delaying the first reproduced video signal by one horizontal scanning period in response to the dropout detection signal from 1. C1, C2 and both individual contacts CI, C2
13 is a delay circuit that delays the reproduced video signal by one horizontal scanning period; and 13 is a delay separation means that separates the reproduced video signal into a luminance signal and a color difference signal. It is a comb-shaped filter. Although not shown in the wtJ3 diagram, this comb filter 13 has an addition circuit and a subtraction circuit having the same configuration as in FIG. 1. The above configuration is similar to the conventional example.

The comb filter 13 separates the reproduced video signal into a luminance signal Y and a color difference signal C, and supplies the luminance signal Y to a synchronization signal processing means 14 and the color difference signal C to a color difference signal processing means 15.

The color difference signal processing means 15 includes a color converter 15a that converts the color difference signal to a standard frequency, a reference frequency oscillator 15b, and a reference frequency oscillator 15b. In order to automatically adjust the frequency of the color difference signal C, a phase comparator 15c compares the phase between the frequency of the output from the color converter 15a and the frequency of the output of the reference frequency oscillator 15'b, and the output of the phase comparator 15c is Filtering low-pass filter 15 d
'tl'E controlled oscillator 15e. on the other hand,
The synchronization signal processing means 14 generates horizontal and vertical first synchronization signals 141 . A synchronizing signal separating means 14a for separating Vl, and a second synchronizing signal synchronized with the first synchronizing signals H1, V1 based on the first synchronizing signals H1, Vl output from the synchronizing signal separating means 14a. a synchronizing signal forming means 14b for forming the second synchronizing signals H2, V2;
2, and switches the first synchronization signals H1, Vl included in the luminance signal Y to the second synchronization signals H2, v2 and outputs the second synchronization signals H2, v2. Reference numeral 16 denotes a reproduced video signal synthesizing means for synthesizing the color difference signal C and the luminance signal Y via the synchronizing signal switching means 14c to form a reproduced video signal. OUT is a means for outputting a reproduced video signal.

In such a configuration, if a reproduced video signal is input 111s10 after the video signal via the input terminal IN, and a signal drop-out occurs in the reproduced video signal, the above-described operation causes the comb filter 13 to of,
The color difference signal C is given to the color difference signal processing means 15, and the luminance signal Y is given to the synchronization signal processing means 14. The color difference signal C processed by the color difference signal processing means 15 is output to the reproduced video signal synthesis means 16.

In the synchronization signal processing means 14, the first synchronization signals H1 and Vl included in the luminance signal Y are separated by the synchronization signal separation means 14a and then input to the synchronization signal formation means 14b.

This synchronizing signal forming means 14b forms second synchronizing signals H2, V2 from the inputted first synchronizing signals H1, Vl in synchronization with these synchronizing signals H1, Vl. The synchronizing signal forming means 14b outputs the formed second synchronizing signals H2, V2 to the synchronizing signal switching means 14c. The synchronization signal switching means 14c selects a first synchronization signal i-+ included in the luminance signal Y.
i.

(2) Replace 1 with second synchronization signals H2' and V2, and output the second synchronization signals H2 and V2 to the reproduced video signal synthesis means 16. The reproduced video signal synthesis means 16 synthesizes the color difference signal C from the color difference signal processing means 15 and the luminance signal Y passed through the synchronization signal processing means 14, and outputs the synthesized signal to the output terminal OUT.

In this way, in this embodiment, even if a dropout occurs in the playback video signal input to the input terminal IN, the playback video signal with the dropout corrected can be output from the output terminal OUT. The image quality on the screen can be improved.

Although the above embodiments have been explained based on the NT and SC systems, it goes without saying that the present invention can be similarly applied to other systems such as the PAL system and the S E CAM system.

(Effects) As described above, according to the present invention, the synchronization signal separation means for separating horizontal and vertical first synchronization signals from the luminance signal, and the first synchronization signal outputted from the synchronization signal separation means, a synchronization signal forming means for forming a second synchronization signal synchronized with the first synchronization signal; and a synchronization signal forming means that operates in response to input of the second synchronization signal to replace the first synchronization signal included in the luminance signal with a second synchronization signal and output the same. and a reproduction video signal synthesis means for synthesizing the color difference signal and the luminance signal via the synchronization signal switching means to form a reproduction video signal. Even if a dropout occurs in the luminance signal, a playback video signal can be formed by replacing the dropout-affected synchronization signal with a different synchronization signal that is synchronized with it and combining it with the luminance signal. This makes it possible to always ensure good image quality without being directly affected by the image quality of the CRT display screen.

[Brief explanation of drawings]

FIG. 1 is a dropout correction circuit diagram of a conventional example, FIG. 2 is a timing chart of each signal for explaining the conventional example, and FIG. 3 is a dropout correction circuit diagram of an embodiment of the present invention. It is an out correction circuit diagram. 10 is a video signal demodulation section, 11 is a dropout detection circuit, 12 is a switching circuit, 13 is a comb filter, 14
15 is a color difference signal processing means, and 16 is a reproduced video signal synthesis means. Applicant Sharp Corporation Representative Patent Attorney Oka 1) Hide Kazu

Claims (1)

[Claims] (1) A dropout detection circuit that detects a dropout in a reproduced video signal, a delay separation means that delays the reproduced video signal and separates the reproduced video signal into a luminance signal and a color difference signal, and the dropout detector. and a switching circuit that selects and outputs the reproduced video signal or the reproduced video signal delayed by the delay separation means in response to a dropout detection signal output from the circuit, wherein the delay Horizontal from the luminance signal output from the separation means. synchronous signal separating means for separating a first vertical synchronous signal; and synchronous signal forming means for forming a second synchronous signal synchronized with the first synchronous signal based on the first synchronous signal output from the synchronous signal separating means. a synchronization signal switching means that operates in response to the input of the second synchronization signal to replace the first synchronization signal included in the luminance signal with a second synchronization signal and output the second synchronization signal; a color difference signal;
and a reproduced video signal synthesizing means for synthesizing the luminance signal via the synchronizing signal switching means to form a reproduced video signal.