JPH0153834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a still image reproduction circuit for a two-head helical scan VTR.

(b) Prior art 2-head helical scan for recording azimuth
When a VTR stops running the tape, it is possible to alternately interlace playback of the video tracks of odd and even fields. In particular, as shown in FIG. It is well known that if the tape running is stopped so that the values match, it is possible to display a stable still image playback screen free of noise. However, it is also known that still images reproduced in this manner cause skew distortion and vertical shaking. Skew distortion occurs because the horizontal synchronization period of the interlaced playback output is discontinuous at the switching part of the head output, and it causes a shift in the scanning direction of the video track (α _H ).
If it is set to an integral multiple of 0.5H (where H is the horizontal synchronization period), skew distortion can be eliminated. Therefore, in many standards regarding recording patterns, (α _H ) is selected as 0.5H or 1.5H for the deviation in the scanning direction. Furthermore,
The standard called 8mm video also sets the scanning direction deviation (α _H ) to 1H in accordance with the NTSC recording pattern.

Further, it is known that vertical vibration during still playback is caused by fluctuations in the vertical synchronization period. For example, in FIG. 1, when the video head scans from the playback start end of A track ( _TA ) to the playback end of B track (T _B ), the video head scans the outside of the A track end and B track start end. Because the extra scanning is done by exactly _2αH , the vertical synchronization signal on the B track side is
It will be delayed by 2α _H. Therefore, in a VTR with a large deviation in the scanning direction, the amount of shaking will also be large.
Therefore, it has been proposed in the past to insert a pseudo vertical synchronization signal in place of the original vertical synchronization signal when reproducing the B-side track (Japanese Patent Application Laid-Open No. 163966/1983).
However, simply correcting the vertical synchronization period will not eliminate the misalignment of the horizontal scanning lines on the playback screen.
One field remains vertically offset relative to the other field.

(c) Purpose of the Invention The present invention has been made in view of the above-mentioned points, and is directed to a VTR in which the deviation in the scanning direction of the video track is 1H. This eliminates the vertical shaking and vertical shift that occur during image playback.

(d) Structure of the Invention The present invention is characterized in that a 1H delay line in the dropout correction circuit is used to delay the head output during still image reproduction.

(E) Embodiment Hereinafter, an embodiment will be described in which the present invention is applied to an 8 mm video in which the deviation in the scanning direction is 1H when recording an NTSC color signal.

In the 8 mm video of this embodiment, the reproduction output switching circuit 1 alternately selects the reproduction output of the A head H _A and the _B head HB based on the head output switching signal RF, and the selected output is sent to the reproduction amplifier 2. After amplification, the signal is distributed and supplied to a color signal processing system, a brightness processing system, and a tracking control system. The brightness processing system first inputs the amplified output (FM modulated video signal) to the first switching circuit 3 and dropout detection circuit 4 in order to perform dropout compensation, and the switching output inputs the amplified output (FM modulated video signal) to the 1H delay circuit (glass delay line) 5. It is fed back as another input to the first switching circuit 3 via the input signal. The switching output and the 1H delay output are input to the next stage noise canceller circuit 6, where they are converted into a noise-free FM demodulated video signal. Note that the noise canceller circuit is a well-known circuit that is often used in β-type VTRs, so a description of its operation will be omitted. The noise canceller output passes through the next stage de-emphasis circuit 7 and is then mixed with the color signal derived from the color signal processing circuit. On the other hand, the tracking control system separates the reproduced pilot signal containing the crosstalk component from the amplified output via the low-pass filter 8. This reproduction pilot signal is input to a mixing circuit 11 together with a reference signal derived from a reference signal generating circuit 10 based on the output of a system controller 9 which inputs a head output switching signal RF. The mixed output is input to the tracking control circuit to realize video head height control (DTF control) and capstan rotation control ATF.

The circuit operation described above is a well-known normal playback operation for 8 mm video, and is not a feature of this embodiment.

In this embodiment, a command signal to stop the tape is issued from the system controller circuit 9 to which the head output switching signal RF is input, and the command signal is issued in anticipation of a mechanical delay when tape running is stopped. Therefore, the positional relationship between the head and the video track when the tape stops running is specified as shown in FIG. 1, and the reproduction pilot signal of the corresponding track is also specified as the first signal _f1 . Therefore, the reproduction pilot signal of the _B track reproduced by the B head HB is specified as the fourth signal _f4 .

Therefore, when the tape is stopped running, the first signal and the fourth signal are alternately derived from the reference signal generating circuit 10 controlled by the system control circuit 9, and the first signal and the fourth signal are alternately outputted to each video track of both heads H _A and H _B A and B.
Play 100%.

In the case of the 8mm video in this example, that is, when recording an NTSC color signal in standard mode, the A head
When switching the playback output of H _A to the playback output of B head H _B , an extra range of 2H is played back, so the field on the A track side becomes 2H longer.

Therefore, in this embodiment, the FM reproduction brightness signal of head _A is delayed by 1H. Because of this delay, a dropout compensation device that also doubles as a noise canceller
A 1H delay circuit 5 is used. Therefore, the second switching circuit 12 inputs the output of the latter stage of the first switching circuit 3 and the output of the latter stage of the 1H delay circuit 5, and outputs a delayed signal or a non-delayed signal according to the control signal derived from the system control circuit 9. Selected. This control signal is the head output switching signal RF
If the reproduction output switching circuit 1 selects the A head output when a high level signal is input, the control signal may be in phase, but if polarity reversal is required, the system controller This can be done using circuit 9.

Note that when the first switching circuit 3 or the second switching circuit 12 selects the delayed signal, the same signal is input to the noise canceller circuit 6 at the subsequent stage, so that noise is not canceled.
Therefore, according to the present embodiment, since the luminance signal component is delayed by one field, the vertical synchronization period becomes constant and the deviation of the horizontal scanning line is also eliminated.
Note that the color signal components are not delayed, and the luminance and color are shifted by two horizontal scanning lines in one field, but there is no visual problem with the color shift. Also, in the above explanation, DTF
I explained using an 8mm video with a servo as an example.
Even with 8mm video without DTF servo,
If the tape is stopped at the noise tracking position as shown in FIG. 1, the above-described still image reproduction circuit can be applied as is. Further, in the above explanation, a track pattern recorded in the standard mode of the NTSC color signal is reproduced, but since α _H is 1H in the CCIR long-time recording mode, the above-mentioned circuit can be applied as is. However, since the CCIR standard mode track pattern has _αH of 2H, the vertical shift will not be eliminated even if the circuit described above is used, but it will be reduced. Furthermore, in this embodiment, in order to stop the tape running in accordance with a specific video track,
Although the switching phase of the second switching circuit 12 is specified without identifying the playback output, if the video track is not specified, the pilot signal frequency, playback output level, vertical synchronization period, etc. during the playback output are detected. , just specify the switching phase, and DTF
Especially for 8 mm videos that do not have a servo, the simplest method is to detect and specify the playback output level.

(f) Effects of the Invention Therefore, according to the present invention, a clear and stable still image can be projected by using the 1H delay circuit for dropout compensation, and the effect is great.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the relationship between a video track and a still image reproduction scan trace, and FIG. 2 is a block diagram of an embodiment of the present invention. Explanation of main drawing numbers 5...1H delay circuit, 3...1st
Switching circuit, 12...second switching circuit.

Claims (1)

[Claims] 1. A video track of a field unit for 1H in the scanning direction using two heads with different azimuths.
Azimuth recording is performed while shifting the head, and the playback output of each head is alternately selected based on a head output switching signal that is inverted at the field period during normal playback to form a continuous playback FM video signal, and the playback FM
In a two-head helical scan VTR which derives a video signal through a dropout compensation circuit, each head is configured to alternately play back two adjacent video tracks at a field period when playing still images, and A still image reproducing circuit comprising a switching circuit that alternately selects an input and an output to a 1H delay circuit constituting a dropout compensation circuit in synchronization with the head output switching signal.