JPH0531877B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to color image reproduction of digital video signals, and particularly to reproduction of slow and slow images in digital VTRs.
The present invention relates to image reproduction suitable for variable speed reproduction of still images and the like.

Digital VTRs record and reproduce digitized video signals, but because the number of recording bits increases, multichannel recording is performed in which data is divided into multiple channels and recorded. An example of a recording format on a helical scan type tape is shown in FIG. 1a. In this example, the data is divided into 1/3 of the screen and recorded. For example, channel A records data on the left side of the screen, channel B records data on the center of the screen, and channel C records data on the right side of the screen. In normal playback, in which the tape is played back at the same tape speed as during recording, the data of each channel is played back along the solid line arrows in FIG. 1a.
On the other hand, in variable speed playback such as slow, still, and fast forward playback, which is played back at a tape speed different from that during recording, the signal is played back along the dotted arrow. Therefore, the reproduced image obtained by variable speed reproduction is as shown in Fig. 1b.
As shown in the figure, the image is a composite of signals from multiple fields. On the image, the cross-hatched area is a region called a noise band that occurs between tracks, and it is impossible to reproduce the image in this area.
Therefore, this area is modified to be replaced with a highly correlated signal to reproduce an image with less deterioration in image quality.

In digital VTRs, corrections are made even during normal playback, but the situations of corrections are different between normal playback and variable speed playback. In normal playback, the signal of the entire screen can be played back, so it is extremely rare to modify several fields in the same place continuously. However, for example, in the case of stills with variable speed playback, the nozzle band is Since it occurs at a fixed location, it is necessary to continuously modify the same location. Therefore, even if a retouching method is effective during normal playback, there is a problem in that when the retouching method is applied during variable speed playback, image quality deterioration due to the retouching becomes extremely large.

For an NTSC composite format television signal, for example, as shown in Figure 2a, when a line that has an error and needs correction is corrected using the signal of an adjacent line whose color subcarrier phase matches that of the previous field, For stills during variable speed playback, for example, each line of the first field in the first frame (combined initial first field and second field) (in the figure, each line is ) is used as a modification signal for the next field, and is modified one after another as shown in the figure. Therefore, in variable-speed playback of still images, the image quality deteriorates significantly because the modified data moves from the bottom to the top on the screen, as shown by the dots in FIG. 2a. In other words, even if the modification causes little deterioration in image quality during normal playback, the modification results in significant deterioration in image quality during variable speed playback.

An object of the present invention is to provide means for reducing image quality deterioration due to noise in a digital video signal reproducing apparatus that performs normal reproduction and variable speed reproduction.

In order to achieve the above object, the present invention provides a digital video signal playback device that performs normal playback and variable speed playback.
The present invention includes a plurality of different types of correction circuits, and is configured to switch between the plurality of correction circuits for normal playback where the tape speed is the same during recording and variable speed playback where the tape speed is different during recording.

Hereinafter, the present invention will be explained in detail based on Examples.

FIG. 3 is a diagram showing the main part of an embodiment of the present invention. In this embodiment, the modified signal for normal reproduction is obtained from the output of switch B, and the modified signal for variable speed reproduction is obtained from the output of switch A. Next, the operation of this embodiment will be explained. The video signal, in which the video signal S is replaced by the modified signal Sr by the switch D in accordance with the modification control signal Sc, is written into the field memory 3. On the other hand, the modified signal Sr is a video signal delayed by one field in the field memory 3.
The signals passed through line memories 1 and 2 are selected by switch A and switch B. Switch B selects and outputs a and b for each field, and the modification signal Sr obtained from this is the one explained in FIG. 2 and is used for modification during normal playback. On the other hand, switch A selects and outputs b, a, b, and c with a period of 4 fields, and produces a correction signal as shown by the dotted line in Figure 2a, which is used for correction during variable speed playback. It will be done. In this case, since the modified signal Sr returns to its original position every four fields, the problem of the modified signal moving from the bottom to the top as described above is solved. Specifically, as shown in FIG. 2b, in order to control the correction signal so that it returns to its original position every four fields,
This prevents the noise band from rising higher (or lower). Then, in the selection circuit 4, an identification signal Sr for normal playback and variable speed playback is provided.
Select and connect switch C to the output of switch B or switch A according to . Note that normal playback and variable speed playback can be easily distinguished by, for example, detecting the tape speed.

FIG. 4 is a block diagram of main parts of another embodiment of the present invention. Switch F is switched from video signal S to modified signal Sr by a modified control signal. In this embodiment, during normal playback, signals are always written into the field memory 6 with switches G and H always closed to create a modified signal Sr, and during variable speed playback, for example, the noise band area is written with switches G and H closed.
A plurality of types of modification signals are used by generating modification signals from a state in which H is turned off and writing to the field memory 6 is prohibited. Next, the operation will be explained. The output signal of the field memory 6 is a signal whose chroma phase polarity has been inverted by the chroma inversion circuit 5, and a signal of the field memory 6, which are selected by switch E, and the signal of the line of the previous field having the same line number as the current field. Alternatively, the chroma-inverted signal can be converted into a modified signal Sr.
shall be. Switch E selection is made by switch control circuit 7.
This is controlled by comparing the field information Sf stored in the field memory 6 with the field information of the current image and selecting a signal so that the color subcarrier phase matches.

Note that the switches G and H are controlled by the selection circuit 8 during normal playback and variable speed playback, and as mentioned earlier, the switches are open in the nozzle band area during variable speed playback. control. This is because, for example, when the nozzle band area is fixed, such as in still shooting, if the switch is closed, the correction signal will become more and more degraded by the chroma inversion circuit each time it passes through the chroma inversion circuit. This is to avoid That is,
By passing the information stored in the field memory through the chroma inversion circuit only once at most, a good corrected signal that prevents this deterioration can be obtained. Note that the identification signal R for normal playback and variable speed playback can be easily identified by, for example, the tape speed. Furthermore, since the noise band portion is also concentratedly modified, it is possible to determine whether it is a noise band or not by looking at the modified region, for example, in units of several lines.

As described above, according to the present invention, it is possible to reproduce an image with less deterioration due to correction in both normal reproduction and variable speed reproduction, and the obtained effects are significant.

In the embodiment described in this text, the information of the previous field is used for the modified signal during normal playback, but it is clear that this may be information such as one line or two lines before the current field.
Furthermore, in the present invention, a method has been described in which the correction is switched according to the normal playback mode and the variable speed playback mode. It is also possible to reduce image quality deterioration by switching and correcting.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the recording format on tape and variable speed playback images in a digital VTR.
FIG. 2 is a diagram of a modification method using information of the previous field, and FIGS. 3 and 4 are configuration diagrams of essential parts of an embodiment of the present invention. 1, 2... 1 line memory, 3, 6... Field memory, 4, 8... Selection circuit, 5... Chroma inversion circuit, 7... Switch control circuit.

Claims (1)

[Scope of Claims] 1. A digital video signal reproducing device for reproducing a digitally recorded image signal, comprising: 1
A field memory for temporarily storing image data for a field, and a signal for a code error that cannot be corrected during normal playback, which is played back at a playback speed equal to the tape speed at the time of recording, to the image data of one field before. Alternatively, a first modification circuit for replacing image data with a first modification code that is image data of one field and one line before, and a variable speed playback that reproduces at a playback speed different from the tape speed during recording, error correction is not performed. The possible sign error signal is 1
The first modification code is the image data before the field, or the image data from one field and one line before, or the second modification code is the image data from one field and two lines before. a selection circuit that selectively outputs the output of the first modification circuit and the output of the second modification signal according to the playback speed; and a modification control signal that is generated according to the playback speed. 1. A digital video signal reproducing device comprising: a first switch that selectively outputs the output from the selection circuit and the image data read from the magnetic tape in accordance with the above. 2. The first modification circuit includes a line memory for temporarily storing one line of output from the field memory, and a line memory for selectively outputting the output from the field memory and the output from the line memory. 2. The digital video signal reproducing apparatus according to claim 1, further comprising a second switch. 3 The second modification circuit includes a line memory for temporarily storing one line of output from the first modification circuit, and an output from the field memory and an output from the first modification circuit. 3. The digital video signal reproducing apparatus according to claim 2, further comprising: a third switch for selectively outputting the output from the line memory. 4. In a digital video signal reproducing device that reproduces a digitally recorded image signal, 1
A field memory for temporarily storing image data for a field, and a signal of a code error that cannot be corrected as image data from one field before, an image obtained by chroma inverting the image data from one field before. A correction circuit for outputting instead of the correction code that is data compares the field information stored in the field memory with the field information of the current image, and adjusts the output of the correction circuit so that the color subcarrier phase matches. a first switch for selectively outputting the output of the switch control circuit and the image data read from the tape in accordance with a selected switch control circuit and a modification control signal generated in accordance with a playback speed; During normal playback, the output signal selected by the first switch is written into the field memory and simultaneously output as an output signal, and during variable speed playback, the output signal selected by the first switch is written into the field memory and simultaneously output as an output signal.
1. A reproducing device for a digital video signal, comprising a selection circuit for inhibiting writing of an output signal selected by a switch into the field memory.