JPH055437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dropout compensation device included in a playback system of a recording/playback device such as a video tape recorder.

[Conventional technology]

Video tape recorder (hereinafter referred to as VTR)
A playback system of a recording/playback device such as the above is equipped with a line memory that stores data for one scanning line obtained by A/D conversion of an input playback signal, and the line memory is activated depending on whether or not a dropout occurs in the input playback signal. As a device for controlling and compensating for dropout, there is, for example, a device disclosed in "Broadcasting Technology" Vol. 37, No. 11, p. 176.

FIG. 3 is a block diagram of the configuration of the dropout compensator according to the prior art. In the figure,
1 is a line memory that stores one scanning line of A/D-converted data of the input playback signal, 2 is a bypass line that bypasses line memory 1, and 3 is a memory write gate that controls the write operation of line memory 1. The circuit 4 is a dropout compensator output switching circuit that selects the output of the dropout compensator depending on whether or not a dropout occurs.

Next, the operation will be explained. The A/D converted data of the input reproduction signal is input into the line memory 1 and the bypass line 2 in parallel. Whether or not a dropout has occurred in the input playback signal can be determined by checking, for example, a VTR.
In the FM demodulation system, it is detected from the envelope of the reproduced FM signal and sent to the dropout compensation device as a dropout detection signal. In this example, if the dropout detection signal is at the "H" level when a dropout occurs, and the dropout detection signal is at the "L" level otherwise, then if there is no dropout in the input playback signal, the memory write gate circuit Since the gate 3 is open and a memory write pulse is input to the line memory 1, input data is written to the line memory 1 every moment. When the line memory 1 becomes full, it returns to the starting address of the line and rewrites new data. On the other hand, the dropout compensator output switching circuit 4 selects the output of the bypass line 2 when the dropout detection signal is at the "L" level, and the output of the dropout compensator becomes data through which the input data passes through.

When a dropout occurs in the input reproduction signal, the dropout detection signal becomes "H" level, and the gate of the memory write gate circuit 3 is closed. Then, since the memory write pulse cannot pass through the memory write gate circuit 3, the line memory 1
Write operations to are prohibited. That is, when a dropout occurs, image information from one horizontal scanning period before is stored in the line memory 1 for the part where the dropout occurs. The dropout compensator output switching circuit 4 selects the readout output of the line memory 1 when the dropout detection signal is at the "H" level, and instead of the dropout signal as the output of the dropout compensator, This is supplemented with the signal stored in the line memory 1 from the previous horizontal scanning period. In this way, when a dropout occurs, the part where the dropout occurs is always compensated for with the signal from one horizontal scanning period ago.

[Problem that the invention seeks to solve]

As mentioned above, the conventional dropout compensator is configured to always compensate for the dropout portion with the signal from one horizontal scanning period before, so the screen where one field's worth of image information is divided into multiple tracks and recorded and played back. In the case of split-type VTRs, there was a problem in that dropout compensation could not be performed using appropriately correlated signals.

This will be explained in detail with reference to FIG. FIG. 4 is a timing chart showing the time axis shift process of a split-screen VTR described, for example, in "Hitachi Hyoron, Vol. 67, No. 5," pages 63 to 66. Figure a shows a video signal for about one field, and the shaded portion VBL is the vertical blanking period. In the example shown in FIG. 4, the video signal for one field is divided into four parts and recorded on four tracks. To this end, as shown in Section 4b, a time axis shift process is performed to remove and distribute the vertical blanking period between each of the four divided image information, and a no-signal period is applied between each divided image information. and then record it. During playback, the head is switched during this no-signal period to prevent image information from being lost due to skew at the head switching point, and the time axis fluctuation correction device restores the time axis as shown in c in the same figure. .

However, when the dropout compensation device described as a conventional technique is used in such a split-screen VTR, the conventional dropout compensation device always compensates for the dropout portion with a signal from one horizontal scanning period earlier. If a dropout occurs in the first scanning line of the divided image information, the dropout portion is compensated for by a signal from one horizontal scanning period before, that is, a no-signal period, and a signal with an appropriate correlation is used to compensate for the dropout. There was a problem with not being able to compensate for dropouts.

This invention was made to solve the above-mentioned problem, and even if a dropout occurs in the first scanning line of divided image information in a split-screen VTR, it is possible to maintain appropriate correlation. The object of the present invention is to obtain a dropout compensator capable of compensating dropout for a certain signal.

[Means for solving problems]

The dropout compensation device according to the present invention includes a line memory that stores input image information, and a case where a dropout occurs in the input image information or when a blanking portion corresponding to a joint section of each divided image information divided into a plurality of pieces is input. includes a memory write gate circuit that prohibits write operations to the line memory, and selects and outputs the read output from the line memory when dropout occurs, and outputs the input image as it is when there is no dropout. It is equipped with a dropout compensator output switching circuit.

[Effect]

In this invention, while input image information is stored in a line memory, if there is no dropout in the input image information, the image information is output as is through the bypass line, and on the other hand, if dropout occurs in the input image information or it is divided into multiple pieces. When the blanking portion corresponding to the joint section of each divided image information is input, the write operation to the line memory is prohibited by the memory write gate circuit, and furthermore, when the dropout occurs, the dropout compensator output switching circuit The read output of the line memory is selected as the dropout compensator output.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of a dropout compensator in one embodiment of the present invention. In this figure, the same reference numerals as in FIG. 3 indicate the same parts. 5 is a write gate circuit of the line memory 1, and unlike the conventional example shown in FIG. 3, a blanking pulse is added as a gate input. 6 is an inverter that inverts the level of the blanking pulse;
7 is an AND gate which receives the output of the inverter 6 and the dropout detection signal as input;
The output of the gate 7 serves as a control input of the dropout compensator output switching circuit 4.

Next, the operation will be explained. The blanking pulse is a signal that is at "H" level during a blanking period corresponding to a joint section of divided image information divided into a plurality of pieces, and is at "L" level during other periods. For example, when a predetermined number of horizontal synchronizing signals separated from the reproduced signal are counted, that is, when the horizontal synchronizing signals are counted by the number of horizontal scanning lines constituting the divided image information, the output is set to "H" level. When the ranking period ends and the first horizontal synchronization signal of the next divided image information is detected, this can be generated with a circuit configuration that outputs an "L" level.

Therefore, during the period when the blanking pulse is at the "H" level, that is, during the blanking period corresponding to the joint section of divided image information divided into a plurality of pieces, the memory write gate 5 is closed, so no write operation to the line memory 1 is performed, and Since the output of the inverter 6 is at the "L" level and the output of the AND gate 7 is also at the "L" level, the dropout compensation output switching circuit 4 selects the output of the bypass line 2. Therefore, during the blanking period, no write operation is performed to the line memory 1, and the output of the bypass line 2 is used as the output of the dropout compensator, regardless of whether a dropout has occurred.

Next, during the period when the blanking pulse is at the "L" level, that is, during the video period other than the blanking period corresponding to the joint section of the divided image information divided into a plurality of parts, the memory write pulse is input to the run-in memory 1 through the memory write gate 5. Whether the dropout detection pulse is "H" or "L" depends only on whether the dropout detection pulse is "H" or "L". Also, at this time, the output of inverter 6 becomes "H", and the AND
Since the gate 7 is open, the control input of the dropout compensator output switching circuit 4 is also
It depends only on whether the dropout detection pulse is "H" or "L".

Therefore, when the dropout detection pulse is at the "L" level, that is, when no dropout has occurred, the memory write pulse is input to the line memory 1 through the memory write gate 5.
As a result, the write operation of the line memory 1 is performed, and at the same time, the output of the AND gate 7 becomes "L" level, so the dropout compensator output switching circuit 4 selects the output of the bypass line 2.
As before, the input data passes through as is and becomes the output of the dropout compensator.

On the other hand, when the dropout detection pulse is at the "H" level, that is, when a dropout occurs, the memory write gate 5 closes and the write operation to the line memory 1 is prohibited.
The output of the AND gate 7 becomes "H" level, and the dropout compensator output switching circuit 4 selects the readout output of the line memory 1. At this time, if the dropout occurs in a scanning line other than the first scanning line of the divided image information, the dropout portion is compensated for with a signal from one horizontal scanning period earlier, as in the conventional method. Furthermore, if the dropout occurs in the first scanning line of the divided image information, the line memory 1 is not written to the line memory 1 during the blanking period as described above. The data of the last scan line of the previous divided image information is retained, so that the drop-out portion can be compensated for with appropriately correlated signals.

In the above embodiment, the output of the bypass line 2 is selected as the output of the dropout compensator regardless of the presence or absence of dropout during the blanking period. It may be configured to select a certain level. FIG. 2 shows the configuration in this case, and in the figure, the same reference numerals as in FIG. 1 indicate the same parts. Reference numeral 8 denotes a dropout compensator which receives two control inputs, a dropout detection signal and a blanking pulse, and selects one from the following three: the readout output of the line memory 1, the output of the bypass line 2, and a constant level such as the black level. This is an output switching circuit. This dropout compensator output switching circuit 8 outputs a signal at a constant level when the blanking pulse is at the "H" level, regardless of whether the dropout detection signal is at the "L" level or the "H" level. select. If the blanking pulse is “L” level,
When the dropout detection signal is at the "L" level, the output of the bypass line 2 is selected, and when the dropout detection signal is at the "H" level, the read output of the line memory 1 is selected. The writing operation to the line memory 1 is exactly the same as in the above embodiment.

The embodiment shown in FIG. 2 is exactly the same as the embodiment shown in FIG. 1 above in that even if a dropout occurs in the first scanning line of the divided image information, this can be well compensated for. Furthermore, even if a dropout occurs during the blanking period, a signal below the black level is not output as the output of the dropout compensator, so there is no adverse effect on the synchronization detection circuit at the subsequent stage.

Furthermore, in the above two embodiments, a dropout compensation device for a recording/playback device using a split screen method has been described, but the present invention provides a dropout compensation device for a recording/playback device using a channel splitting method as well as a split screen method. It can also be applied when
The same effects as in the above embodiment are achieved.

〔Effect of the invention〕

As described above, according to the present invention, in a split-screen recording/playback device, a line memory for storing input image information, and a line memory for storing input image information, and a line memory for storing input image information, A memory write gate circuit is provided which prohibits the write operation to the line memory when the blanking part corresponding to the seam section is input, and when there is no dropout, the input image is output as is, and when dropout occurs, the above-mentioned memory write gate circuit is provided. Since the readout output from the line memory is selected and output, even if a dropout occurs in the first scanning line of the divided image information divided into a plurality of parts, it can be compensated for with an appropriately correlated signal. It has the effect of

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a dropout compensation device according to one embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a dropout compensation device according to another embodiment of the invention, and FIG. 3 is a block diagram showing the configuration of a dropout compensation device according to another embodiment of the invention. A block diagram showing the configuration of the compensation device,
FIG. 4 is a timing chart showing the time axis shift process of a split-screen VTR. FIG. 4a is a schematic diagram of a video signal for one field, FIG. FIG. 4c is a schematic diagram of the time axis restored signal. 1...Line memory, 2...Bypass line,
4... Dropout compensator output switching circuit, 5... Memory write gate circuit, 6... Inverter, 7... AND gate. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. In a dropout compensation device included in the playback system of a split-screen recording and playback device that records and plays back video signals for one field divided into multiple tracks, a predetermined amount of input image information is sequentially updated. When a dropout occurs in the input image information, or when the input is a blanking part corresponding to a seam section of each divided image information divided into a plurality of pieces, the write operation to the memory is prohibited. a memory write gate circuit; and a dropout compensator output switching circuit that selects and outputs the read output from the memory as the output of the dropout compensator when the dropout occurs, and outputs the input image as it is when there is no dropout. A dropout compensator comprising: 2. The dropout compensator output switching circuit selects a constant level equal to or higher than the black level for the period of the blanking portion when a blanking portion corresponding to a seam section of each of the plurality of divided image information is input. The dropout compensating device according to claim 1, wherein the dropout compensating device outputs an output.