JPH01144883A - Dropout correction device - Google Patents

Abstract

PURPOSE:To attain excellent dropout correction by using a reproduced chrominance subcarrier and a synchronizing signal of a direct reproduced composite video signal not subject to delay so as to form a composite video signal again from a luminance signal and a color difference signal after the result of YC separation and color demodulation from a signal retarded by 1H. CONSTITUTION:A dropout detection circuit 9 detects a dropout from a reproduced high frequency signal and gives a dropout detection signal to a switch 8. The switch 8 uses the dropout detection signal to switch signals at contacts a, b and when any dropout takes place, a signal at the contact (a) (re- synthesized composite video signal subject to 1H delay) is outputted externally and when not takes place, the signal at the contact (b) is outputted externally through a contact (c). The composite video signal outputted from the switch 8 and whose dropout is corrected is outputted from an output terminal 10. Thus, excellent dropout correction is applied and stable performance is obtained against time axis fluctuation of the reproduced composite video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a dropout correction device for correcting dropouts that occur when a composite video signal is reproduced from a video recording medium such as a VTR or video disc. .

BACKGROUND ART When a composite video signal is reproduced from a VTR, video disc, etc., a so-called dropout occurs, which is a phenomenon in which the level of the reproduced radio frequency (RF) signal decreases due to scratches, dust, etc. on the recording medium.

Therefore, in order to avoid missing information due to dropout, a dropout correction device is generally used. Hereinafter, a conventional example will be explained using FIG. 2.

FIG. 2 is a block diagram showing an example of the configuration of a conventional dropout correction circuit, in which 21 is an input terminal for a reproduced high-frequency signal;
22 is an FM demodulation circuit, 23 is 1H (H is horizontal scanning period)
24 is a switch, 25 is a dropout detection circuit, and 26 is an output terminal for a composite video signal.

In FIG. 2, one of the reproduced high-frequency signals inputted from the input terminal 21 is FM-detected by the FM demodulation circuit 22, and one is directly sent to the contact b'' of the switch 24 as a composite video signal, and the other is sent to the 1H delay circuit 33. After a delay of 1H, the signal is applied to the contact a' of the switch 24.The other side of the reproduced high-frequency signal is applied to the dropout detection circuit 25.The dropout detection circuit 25 detects the envelope of the reproduced high-frequency signal. , when the amplitude has significantly decreased, a dropout signal is output as a switching signal of the switch 24.The switch 24 switches the significant period of the dropout signal from the dropout detection circuit 25 to the contact a° side, that is, 1H delayed. Select the signal that was selected, and otherwise pass the signal on the contact b° side to contact C°.
In this manner, the reproduced composite video signal is output from the output terminal 26 after being subjected to dropout correction.

In the above explanation, the period during which dropout occurred,
If the signal to be corrected includes a color signal, if the signal from 1H before is replaced as it is, the color subcarrier phase will be shifted by 180", so the color shift will be noticeable on the reproduced screen after correction (replacement). To deal with this, a 1H delayed signal of only the luminance signal may be used instead of the composite video signal as the replacement signal.

Problems to be Solved by the Invention However, the above configuration causes the following problems.

In general, reproduction signals from video equipment such as VTRs and video discs include fluctuations in the time axis direction, which adversely affect reproduced images, so time axis correction is performed to remove fluctuation components. This correction extracts the color burst signal in the composite video signal and converts it to a reference signal (for example, 3.58 M
llz), and the correction amount is controlled based on the phase difference.

Therefore, as mentioned above, if there is a color burst signal whose phase is inverted in the color burst signal section, or if there is no color burst signal whose phase should be compared,
There was a problem in that the time axis correction was not sufficiently performed.

In view of this, the present invention separates the composite video signal delayed by 1H into a luminance signal and a color signal, demodulates the color signal, and then uses a signal that is returned to the composite video signal as the replacement signal. It is an object of the present invention to provide a dropout correction device that can sufficiently perform time axis correction.

Means for Solving the Problems The present invention provides 111
A dropout correction device that replaces a delayed composite video signal with a reproduced composite video signal includes a YC separation circuit that separates the composite video signal from YC (Y: luminance signal, C: chrominance signal) and a chrominance signal from the chrominance signal. a chrominance demodulation circuit for demodulating the 1H delayed composite video signal, a sync/color carrier regeneration circuit for reproducing the sync signal and color subcarrier from the composite video signal in which dropout has occurred, and a 1H-delayed composite video signal from the luminance signal and color difference signal. T S C National Television
This is a dropout correction device equipped with a sionSystem Comm1tee (current color television system) encoder.

Effect of the Invention With the above-described configuration, the present invention separates a composite video signal delayed by 1H by YC as a replacement signal when a dropout occurs, and further converts a color demodulated color difference signal and a luminance signal into a composite signal in which a dropout occurs. By using a 1H-delayed composite video signal that is re-encoded as a composite video signal using the synchronization signal and color subcarrier reproduced from the video signal, deterioration in image quality on the playback screen can be replaced with only the luminance signal described above. This makes it possible to minimize the impact of dropout. Furthermore, even when a dropout occurs during a color burst period, the color burst of the composite video signal delayed by 1H to be replaced is created from the color subcarrier reproduced from the composite video signal in which the dropout has occurred, so their phases are the same. As described above, stable time axis correction is realized without interfering with the operation of time axis correction using color bursts.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a drop-out correction device according to the first embodiment of the present invention, in which 1 is an input terminal, 2 is an FM demodulation circuit, 3 is a 1H delay circuit, 4 is a yc separation circuit, and 5 is a color demodulation circuit, 6 is an NTSC encoder, and 7 is a color demodulation circuit.
8 is a synchronization/color subcarrier regeneration circuit, and 8 is a switch (a, b,
(c indicates each contact), 9 is a dropout detection circuit, and 10 is an output terminal.

The operation of the dropout correction device of the present invention configured as described above will be described below with reference to FIG.

A reproduced high frequency signal reproduced from a VTR, video disc, etc. passes through an input terminal l, and is applied to the FM demodulation circuit 2 on one side and the dropout detection circuit 9 on the other side. The reproduced high frequency signal is demodulated into a composite video signal by the FM demodulation circuit 2,
It is applied to the IH delay circuit 3, the synchronization/color subcarrier regeneration circuit 7, and the contacts of the switch 8. 1 with 1H delay circuit 3
The H-delayed composite video signal is separated into a luminance signal and a color signal by a YC separation circuit 4, where the luminance signal is directly demodulated and the color signal is demodulated into a color difference signal by a color demodulation circuit 5, which is then applied to an NTSC encoder 6. . The synchronization/color subcarrier reproducing circuit 7 reproduces various synchronization signals and color subcarriers from the input composite video signal and supplies them to the NTSC encoder. N.T.
The SC encoder converts the luminance signal output from the YC separation circuit 4, the color difference signal output from the color demodulation circuit 5, the color subcarrier from the synchronization/color subcarrier regeneration circuit 7, and various synchronization signals into NTSC signals. The color signal, that is, the 1H delayed composite video signal is recombined and applied to the contact a of the switch 8.

On the other hand, the dropout detection circuit 9 detects dropout from the reproduced high frequency signal and applies the dropout detection signal to the switch 8. Switch 8 switches the signals at contact A and contact S according to this dropout detection signal, and when a dropout occurs, the signal at contact A side (recombined composite video signal delayed by 1H) is not generated. At this time, the signal on the contact side is passed through contact C and output to the outside. The dropout-corrected composite video signal outputted from the switch 8 in this manner is outputted from the output terminal 10.

As described above, according to this embodiment, as the 1H delayed signal to be replaced at the time of dropout, the luminance signal and color difference signal after YC separation and color demodulation of the IH delayed signal are not delayed. Good dropout correction can be achieved by using the reproduced color subcarrier and synchronization signal of the directly reproduced composite video signal to reconstitute the composite video signal. Furthermore, as described above, since the color burst of the replaced composite video signal is in phase (continuous) with that of the directly reproduced composite video signal, stable time axis correction is also possible.

In this embodiment, the 1H delay circuit is inserted before the YC separation circuit, but the luminance signal, two-color signal, and
Alternatively, it is also possible to insert it into the color difference signal after the luminance signal single color demodulation circuit.

Further, in this configuration, the time difference between the luminance signal and one color signal (or color difference signal) can be easily corrected.

As described in detail, according to the present invention, it is possible not only to perform dropout correction that does not cause color shift or color streaks during dropout correction, but also to compensate for time axis fluctuations in a reproduced composite video signal. It is possible to achieve stable performance even at low temperatures, and its practical value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a dropout correction device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional dropout correction device. 2.22...FM demodulation circuit, 3,23...
...1H delay circuit, 4...yc separation circuit, 5.
... Color demodulation circuit, 6 ... NTSC encoder, 7 ... Synchronization/color subcarrier regeneration circuit, 9.
25...Dropout detection circuit. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2

Claims (1)

[Claims] In a dropout correction device that replaces a composite video signal delayed by 1H with a composite video signal in which a dropout has occurred only during a significant period of a dropout detection signal, a YC separation circuit that separates a luminance signal and a color signal from the composite video signal; a color demodulation circuit that demodulates a color difference signal from the color signal; a synchronization/color subcarrier regeneration circuit that reproduces continuous color subcarriers and a synchronization signal from the dropout-generated composite video signal; A dropout correction device comprising: an NTSC encoder that creates a composite video signal delayed by 1H.