JPS6217432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scan type azimuth recording magnetic recording/reproducing device in which the video head gap angle is slightly different between the A and B heads. The present invention provides a recording still image reproducing device.

An embodiment of the present invention will be described below in comparison with a conventional example.

Conventionally, when a still image is reproduced in a two-head helical scan type azimuth recording magnetic recording/reproducing apparatus, the phase of the vertical synchronization signal of the reproduced video signal with respect to the head switching pulse differs for each field. This phase relationship shifts as the head tracking phase deviates, becomes reversed between the A and B heads when exactly one track (field) deviates, and returns to its original state when it further deviates by one track. 1st
The figure shows the recording pattern and still image reproduction locus in azimuth recording, where a ₁ , a ₂ , and b ₁ , b ₂ indicate the recording patterns of heads A and B, respectively. 2A to 2D show the phase relationship between the synchronization signal of the reproduced video signal and the head switching pulse during the still image reproduction trajectory on the pattern of FIG. 1. In FIG. 2, a indicates a head switching pulse, and a and b indicate an A head section and a B head section, respectively. B, C, and D indicate the trajectories of No. 1, No. 2, and No. 3 in Fig. 1, respectively. This phenomenon results in a phase shift of α _H between adjacent tracks. In the case of _αH , the phase of the vertical synchronizing signal V _S varies by a width of 3H with respect to the head switching pulse.
When a still image is reproduced with the noise band within the vertical blanking interval, the phase of the synchronization signal changes by 1.5H for each field. By the way, in order to prevent vertical synchronization signals from being disturbed by noise bands when still images are reproduced, a pseudo synchronization signal is usually inserted. This synchronization signal is generated with a phase delay compared to the head switching pulse. At this time, as mentioned above, the phase of the synchronization signal of the video signal being reproduced is ± for each field with respect to the periodic switching pulse phase.
It has changed for 1.5H. Therefore, it is desirable that the optimum phase of the pseudo synchronization signal be generated in relation to the periodic phase of the reproduced video signal. Therefore, the pseudo synchronization signal has frame periodicity. Above ±
The polarity of 1.5H changes depending on the position of the noise band during still image playback. In other words, when the noise band is brought close to the vertical synchronization signal, one side of the noise band is ±1.5H, and the other side is -1.5H.
It is becoming. For this reason, originally it would be sufficient to generate the pseudo synchronizing pulse in accordance with the polarity of the ±, but currently the polarity is assigned by fixing it to the phase of the head switching pulse. Therefore, in order to perform still image playback with the optimal phase of the pseudo synchronization signal, the tape is stopped from normal playback and the still image is played back, and the noise band is moved to the vertical blanking section to achieve complete still image playback. There are times when it is necessary to move by one frame in order to make a picture. This is extremely troublesome.

The present invention has been made to solve the above-mentioned drawbacks, and is characterized in that the phase of the pseudo synchronization signal is selected by detecting the position of the nozzle band during still image reproduction.

FIG. 3 shows the configuration of an embodiment of the present invention, in which a motor control signal Mc controls a capstan motor 5 via a motor drive circuit 3 during normal reproduction. When the switching signal (PLAY/STILL) switches to STILL, the differentiating circuit 4 detects this and instantaneously cuts it off, and also applies an electromagnetic brake to the capstan motor 5 via the motor brake circuit 6 to stop the magnetic tape. Stop running. Thereafter, the rotation of the capstan motor is controlled via the gate 2. Control at this time is performed by a slow volume 7 that divides the voltage by +12 [V]. The head switching pulse Sp of 30 [Hz] is divided into 15 [Hz] through a 1/2 frequency divider 9, and further divided into 15 [Hz] with a constant pulse width through a monomulti (hereinafter referred to as MM) 8. Convert to [Hz] pulse signal. The signal of this MM8 output is mixed with the DC output of the slow volume 7 via the diode D and supplied to the capstan motor 5, and the position of the noise band is moved by the slow volume 7.
Further, the MMs 10, 11, and 12 are triggered by both the positive edge and the negative edge of the head switching pulse Sp and operate at 60 Hz. MM1
2 is shifted by 1/120 seconds, as shown in FIG. 4d, and triggers the 1/2 counter 15. The 1/2 counter 15 is shifted in phase and produces two pulses f, g (FIG. 4 f, g) in an inverse relationship to each other at 30 Hz. These two pulses f and g control gates 14 and 13, respectively, and gates 14 and 1
Gates 13 and 14 output synchronizing signals of the MM11 and 10 outputs, respectively. The output signals are input to the MM16 in parallel and trigger the MM16, which generates a pseudo pulse h.
[Figure 4h] is output. FIG. 4i shows an envelope signal for still image reproduction in azimuth recording, where noise occurs near zero where the envelope from the video head output becomes small. The noise band detection circuit 17 consists of a limiter circuit and an AM detection circuit, and detects the noise band e (FIG. 4e) by passing the envelope signal i through the limiter circuit and further performing AM detection. Here, if the output e of the noise band detection circuit 17 does not match the operating state of the 1/2 counter 15 in phase, the output e is reset R. That is, Fig. 4 b, c, e,
It can be seen from f, g, and h that the phase of the synchronization signal where the noise band occurs moves in the delay direction.
When a noise band occurs near the reproduced vertical synchronization signal, a signal of Δt ₁ with a large phase delay is assigned as a pseudo synchronization signal V _D to one field of the vertical synchronization signal, and a signal of Δt with a small phase delay is assigned to the other field. ₂ signals are assigned. Therefore, the phase of the pseudo synchronization signal is selectively determined by determining the phase of the noise band, and the mixture of the vertical synchronization signal and the pseudo synchronization signal is as shown in Fig. 4j. Even if , the optimum phase is reached,
A completely still image is obtained. Further, there is no need to shift the phase by one frame with the slow volume as in the conventional method, and it can be done by one field. Note that although the above embodiment has been established for still image playback, slow playback can also be handled in the same manner. Also, during slow playback, if the reset signal input terminal of the 1/2 counter 15 is connected to the power supply via the resistor r as shown by the broken line in FIG. 3, and the reset signal is continuously input via the slow switch 18, The operation of the 1/2 counter 15 is prohibited and only the synchronizing signal output from the MM10 is input to the MM16. Therefore, a pseudo synchronization signal with a constant phase is provided, the phase variation of the reproduced synchronization signal with respect to the pseudo synchronization signal is within 1.5H, and the vertical variation is averaged within 1.5H. If the reset signal of the 1/2 counter 15 is not switched during slow playback, the noise band will fluctuate by 3H in the process of moving to the vertical blanking section, making it difficult to see. Therefore, the averaging pulse is effective during slow playback. In addition, in the above embodiment, MM10 and 11
MM12 and gate 1 act as synchronizing signal generating means to generate two types of phase signals with large and small phase delays with respect to the video head switching pulse.
3 and 14 and the 1/2 counter 15 act as gate means for determining the phase of the noise band and selectively determining the phase of the pseudo synchronization signal.

As explained above, according to the present invention, since the phase of the noise band is determined and the phase of the pseudo synchronization signal is selectively determined, the phase of the still image of any field is easily set to the optimum phase, and the still image is completely still. You can obtain a clear image.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the pattern in azimuth recording and the still image playback trajectory, and Figure 2 A to D are the phases of the synchronization signal and head switching pulse of the reproduced video signal during the still image trajectory on the pattern in Figure 1. FIG. 3 is a diagram showing the main part of a magnetic recording/reproducing apparatus according to an embodiment of the present invention, and FIGS. 4 a to 4 j are waveform diagrams showing the main part of FIG. 3. 10, 11, 12, 16... Mono multivibrator, 13, 14... Gate, 15... 1/2 counter, 17... Noise band detection circuit, V _S ... Vertical synchronization signal, V _D ... Pseudo synchronization signal.

Claims (1)

[Scope of Claims] 1. A means for detecting a noise band from an envelope signal of a video head output, a synchronizing signal generating means for generating two types of phase signals with large and small phase delays with respect to a video head switching pulse, and a reproduction output. Assigning the phase signal with the larger phase delay to the vertical synchronization signal of the field closer to the noise band appearing on the signal as a pseudo synchronization signal,
An azimuth recording still image reproducing apparatus characterized in that it has gate means for allocating the phase signal having a smaller phase delay as a pseudo synchronization signal to the other field and selectively determining the phase of the pseudo synchronization signal. 2. The gate means is configured to prohibit selection of the phase of the pseudo synchronization signal during slow playback,
The azimuth recording still image reproducing apparatus according to claim 1, characterized in that a synchronization signal whose phase is fixed is used.