JPH0520035B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a helical scan video tape recorder (hereinafter abbreviated as VTR), and in particular provides a method that enables good variable speed playback when one field is divided into multiple tracks and recorded. It is. Conventional technology Rotating 2-head helical scan VTR is VHS
This method is used as a basic method in many VTRs, such as the β method and the β method. In this system, magnetic heads are mounted on a rotating drum at 180 degrees from each other, and two fields (one frame) are recorded on the tape as two tracks during one revolution of the drum. Using the above-mentioned VTR for recording standard format television signals, a wideband video signal n times that of the standard format is divided into n channels of narrowband signals.
There is a way to record channels simultaneously. This will be explained for the case where n=2. The methods for dividing the video signal into two-channel narrowband signals include: (1) Dividing each sample point into two streams. (2) Divided into two series every 1H (horizontal scanning period). There is a method (1985 National Conference of the Institute of Electronics and Communication Engineers)
239), but here we will explain method (2).
As an actual example, a 4MHz band NTSC VTR
It is a band compression method for high-definition television.
The case of recording a video signal using the MUSE method (8MHz band) will be explained. Table 1 shows a comparison of both methods.

[Table] As can be seen from Table 1, if 1H of the MUSE method is expanded twice on the time axis, it becomes almost equivalent to NTSC. Figure 2 shows this situation. a
is the horizontal scanning line number of the MUSE video signal, b,
c indicates the horizontal scanning line number of the video signal expanded and divided into two channels. With such processing, one frame can be recorded in one rotation of the drum by simultaneously recording two tracks in parallel as one field. Note that the 1125th line is omitted because it is a blanking period. In this case, the drum rotation speed is 1800r.pm. Therefore, special playback is also possible using the same concept as for NTSC VCRs. FIG. 3 is a schematic diagram of the format on the tape. In the figure, A and B indicate the top scanning lines of the screen, and C and D indicate the bottom scanning lines. In contrast, the baseband signal of high-definition television has a 20MHz band. For example 16MHz
Even if the band is limited and recorded, it is four times faster than NTSC.
A method of recording using the same concept with n=4 can be considered, but it is necessary to record four tracks per field at the same time. That is, eight heads are attached to one cylinder, and problems such as accuracy, difference in characteristics, contact of the heads with respect to the tape, etc., increase due to the multi-channel head. On the other hand, there is a method of recording a broadband signal by rotating the drum at high speed and increasing the relative speed of the head tape. According to this method, in the above example, the drum rotation will be increased four times, that is, 7200 rpm, and it will be necessary to rotate at a very high speed. This poses new challenges in terms of mechanical system reliability and the like. Therefore, in this case, a practical method would be to use the first method and the second method together. That is, this method divides the signal into two channels and doubles the rotation of the drum. In this case, 2
Channel recording is 3600 rpm, so the number of heads and drum rotation speed are not too big of a problem. The problem with this method is that special playback becomes inconvenient. The recording format on the tape at this time is as shown in FIG. 4, since one frame is recorded every two revolutions of the drum. In the figure, A and B indicate the scanning lines at the top of the screen, and G and H indicate the scanning lines at the bottom. Therefore, in the case of special reproduction, a signal is reproduced in which an image that should appear in the upper half of the screen and an image that should appear in the lower half of the screen are mixed with each other. Problems to be Solved by the Invention As mentioned above, when the drum rotation speed of a VTR is set to N times the frame frequency, the vertical positional relationship on the screen becomes confused during special playback. Means for Solving the Problems In order to solve the above-mentioned problems, the present invention has the following features:
The time axis of the field video signal is expanded by approximately n times, divided into n channels, recorded on n tracks simultaneously, and when one field is sequentially recorded on the tape by N scans, one field is constructed ( The scanning lines from the beginning to the end of the screen are sequentially recorded from the scanning start position to the scanning end position for all of the (n×N) tracks. Effects According to the present invention, with the above-described configuration, a normal screen can be obtained by performing relatively simple processing during special playback. Embodiment An embodiment of the present invention is shown in FIG. This embodiment uses the two-channel division described in the conventional example section, 3600 r.p.
The case of m will be explained. a indicates a horizontal scanning line number of a video signal of high-definition television. b, c
By extending the time axis of the information in a in units of 1H and rearranging it within one field, the scanning line at the top of the screen is recorded at the scanning start position of all tracks, and then the scanning line is recorded at the bottom of the screen as the head advances on the tape. , and the scan line at the bottom of the screen is recorded at the scanning end position. By rearranging the signals in this manner, it is possible to record the track pattern as shown in FIG. When the pattern shown in this figure is specially reproduced, the top and bottom of the screen will not be played back in a jumbled manner. Since information about the entire screen can be obtained in one scan, a normal screen can be reproduced by performing the same processing as in normal reproduction. Furthermore, the rearrangement of the scanning lines shown in Fig. 1 is as follows:
This can be easily realized by using two field memories. Note that the method of extending the time axis of the input video signal and rearranging it in units of scanning lines is not limited to the above embodiment, but the method of extending the time axis in units of 2H, the method of extending the time axis in units of 2H, and the method of extending the time axis in units of 2H, and rearranging odd lines and even lines between b and c. Any method may be used, such as replacing the images, as long as the order of the scanning lines within each track satisfies the condition that the order of the original image is preserved.
Although this embodiment has been described for the case of 2-channel division and double rotation of the drum, similar effects can generally be expected by similar processing for n-channel division and N-times rotation. Effects of the Invention As described above, according to the present invention, in a helical scan VTR, a video signal is time-axis expanded and divided into n channels, n tracks are recorded simultaneously in one scan, and n tracks are recorded in sequential order in N scans. Special playback can be made possible by simple processing when recording one field.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a method according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of a method of time-axis expanding a high-visibility signal of the MUSE system and dividing it into two channels for recording. A schematic diagram of the tape format and screen for the method shown in Figure 2, and Figure 4 shows a baseband high-definition signal that is time-axis expanded and divided into two channels, and the drum is rotated twice to repeat one field twice. FIG. 5 is a schematic diagram of a tape format and screen of an embodiment of the method of recording by scanning.

Claims (1)

[Claims] 1. When recording a video signal as a set of diagonal marks on the magnetic tape by scanning the magnetic tape with a magnetic head, an input video signal with K effective scanning lines per field is provided. a step of extending the time axis approximately n times (n is an integer of 2 or more) using a horizontal scanning line as a unit, and dividing the signal into n channels, and a scanning line thinning operation process based on a predetermined rule for the signals of each channel. Therefore, the video signal is divided into N sets (N is an integer of 2 or more) of video signals, each of which contains information for the entire screen and is composed of approximately K/(n·N) scanning lines. n
Video signal recording characterized in that the video signals of the channels are simultaneously recorded on n tracks that are parallel to each other, and the video signal of one field is divided into n×N tracks by successive N scans and recorded in parallel. Method. 2. The scanning line thinning operation process based on a predetermined rule is characterized in that consecutive (n·N) scanning lines of the input video signal are recorded on mutually different tracks. Video signal recording method. 3. The (n/N) set of video signals obtained by the scanning line thinning operation process preserves the order of the horizontal scanning lines of the input video signal. video signal recording method.