JPS6249792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scan type magnetic recording medium that uses a rotating head to sequentially record and reproduce video signals of one field or an integral multiple thereof as a recording locus inclined with respect to the longitudinal direction of a magnetic tape. This relates to a recording and reproducing system, and is configured so that stable reproduced images can be obtained even when obtaining slow images, still images, or quick images by reproducing at a tape speed different from the tape speed at the time of recording.

Conventionally, in order to perform high-density recording and eliminate crosstalk during reproduction from adjacent tracks, VTRs have been put into practical use in which the azimuth angles of magnetic heads for recording and reproducing adjacent tracks are different.

Figure 1 shows the recording trajectory on the tape of a VTR using two rotary heads A and B with different azimuth angles, A ₁ , A ₂ , A ₃ . . .
B ₁ , B ₂ , B ₃ . . . indicate recording trajectories recorded by rotating head B, respectively.

Now, if we consider the case where this VTR stops running the tape during playback and plays still images, the scanning trajectories of rotating heads A and B during playback are the first.
The result will be as shown in Figure 1, and two tracks with different azimuth angles will be played.

Therefore, half of the screen becomes noise, making it impossible to obtain a good reproduced image. Therefore, if you want to play back with the A head, move the magnetic head in the direction of arrow 2, and if you want to play with the B head, move the magnetic head in the direction of arrow 3.
If B is traced, a good reproduced image without noise can be obtained.

As a method of displacing the magnetic head as described above,
It is common to use a material with a very large piezoelectric effect, such as a piezoceramic element, to create an electro-mechanical transducer that is used as a support arm for the magnetic head to displace the magnetic head.
A description of the above-mentioned electro-mechanical converter will be omitted since it is generally well known.

By using the above method, a good still image without noise can be obtained. However, as shown in FIG. 2, the number of horizontal periods reproduced by one head increases. 1 in Figure 2 shows the head trajectory when the electro-mechanical converter is not used as the support arm of the magnetic head, but if the position of the head is displaced as described above using the electro-mechanical converter, then For example, the scanning locus of the heads will be 4 when the A head is used for reproduction, and 5 when the B head is used for reproduction. Therefore, sections 6 and 7 in the diagram
The number of horizontal synchronization signals increases by the portion indicated by .

For example, the 2nd generation of a VTR called the VHS system.
In the case of time mode, the actual recording tracks A ₂ , B ₁
A horizontal synchronizing signal section (hereinafter referred to as H) of 262.5 is recorded above, and sections 6 and 7 are 1.5H.

In the case of still playback in 2-hour mode on this VHS system VTR, H within the vertical period (1/60 sec)
When we look at the numbers, we get the results shown in Figure 3. 8,
Reference numerals 9 and 10 indicate vertical synchronization signals, section 11 is a period during which the A head reproduces, and section 12 is a period during which the B head reproduces. In addition, each recording track A ₂ , B ₁
It is assumed that the vertical synchronization signal is recorded at the beginning of the video. In the case of still playback above, the interval of vertical sync signals 8 and 9 is 265.5H, and the interval of vertical sync signals 9 and 10 is 265.5H.
The interval is 262.5H and the number of H in the vertical period is 3H
There will be an error of .

In the case of still playback, since the above scanning is repeated, the number of H's within one vertical period is repeated with an error of 3 H, and this causes 3 H's of V-dancing, or 3 H's vertical wobbling, when viewed on the screen.

The present invention attempts to reduce this 3H vertical fluctuation using a time axis correction device.

FIG. 4 shows the basic structure of the time axis correction device according to the present invention. 15 is an input terminal, and 16 is an output terminal. 17, 18, 19, and 20 are delay elements each having a delay time of 0.5H, and in this example,
It uses CCD. 21 is an output switching circuit;
22 is the input signal of the input terminal 15, that is, the undelayed output; 23 to 26 are the delay elements 17 to 2;
0 each delayed output, ie 0.5H delayed output, 1H delayed output, 2H delayed output, etc. Each of these outputs is switched by an output switching circuit 21 to correct the time axis.

In the case of still playback in the 2-hour mode of the above-mentioned VHS VTR, 3H V dancing occurs as described above.

Therefore, by outputting the outputs of the A head and B head as appropriately delayed outputs, the time axis can be corrected and the vertical fluctuation can be reduced. In other words, in the above example, during period 11 when the A head is playing, output 24 is delayed by 1H, and
By providing the output 22 which remains undelayed during the period 12 played in the B head, the vertical period 14A
is 264.5H, the next vertical period 14B is 263.5H, and the error in the number of H within both vertical periods is 1H.
In this case, a vertical shake of 1H will occur, but when viewed with the human eye, a vertical shake of about 1H will not be noticeable.

When the tape speed is lower than the normal speed, so-called slow playback, the same thing as still playback can be performed.

However, as mentioned above, when the delayed outputs from each delay element are combined to form the overall output, if the levels of the video signals transmitted to the delay elements are not completely aligned, the overall output will fluctuate in level. occurs, causing flickering on the screen.

Therefore, the luminance signal of the video signal is FM modulated, the carrier color signal is converted to a low frequency, the above signals are added and recorded, and the reproduced FM modulated signal and the low frequency converted carrier color signal are added. In recording and reproducing devices that separate signals and perform signal processing to restore the original luminance signal and carrier color signal, time axis correction for still, slow, and double-speed playback is performed using the above-mentioned FM modulation signal and low-frequency conversion. By performing this before separating the added signal of the carrier color signal and performing signal processing, it is possible to eliminate flickering that occurs on the screen.

That is, in the time base correction device as shown in FIG. 4, since the signal transmitted to the delay elements is an FM signal, there is no need to accurately align the output levels of each delay element.

As described above, in a helical scan type video signal recording and reproducing apparatus, when the video signal is reproduced at a tape speed different from the standard tape speed, the number of horizontal scans within the vertical period of the reproduced video signal is different. By providing a plurality of delay means that delay a certain period of time and an output signal switching circuit that sequentially switches the output of each delay means according to the playback tape speed, it is possible to change the delay time in units of vertical periods by simple switching control. By combining the delayed signals, the error in the number of horizontal scan lines within each vertical period is corrected to a maximum of 1H, and a stable reproduced image can be obtained.

Furthermore, in the present invention, since the frequency modulated and recorded video signal is configured to be delayed by a delay element without being demodulated, the level of the video signal does not change due to the difference in delay time. be.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the recording pattern on a magnetic tape by a helical scan VTR and the head scanning locus during still playback, and Figure 2 is a diagram showing the relationship between the head scanning locus and recording pattern during still playback. This figure shows the relationship between the reproduction period of each head and the vertical synchronization signal period during still reproduction, and FIG. 4 is a block diagram showing one embodiment of the present invention. 15...Input terminal, 16...Output terminal, 17,
18, 19, 20...Delay circuit, 21...Switching circuit.

Claims (1)

[Claims] 1. The tape speed at the time of recording is determined by a magnetic tape on which one field of video signals frequency-modulated is sequentially recorded as one recording trajectory by a rotating magnetic head as a recording trajectory inclined with respect to the longitudinal direction of the magnetic tape. and a plurality of delay means for delaying the video signal for a certain period of time when the recorded video signal is played back at different tape speeds, and an output signal switching circuit that sequentially switches the output of each delay means in accordance with the playback tape speed. and without frequency demodulating the reproduced signal from the rotating magnetic head,
The above-mentioned delay means and output signal switching circuit selectively delay the vertical synchronization signal by varying the delay time in time units, and reduce the difference in the number of horizontal scanning lines within each vertical synchronization signal period to one horizontal scanning line. A magnetic recording/playback method characterized by demodulating after the following: