JPS5938644B2 - Video signal reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a magnetic tape is run in a state of being wrapped around the entire circumference of a guide drum, and one magnetic head is in contact with this magnetic tape. The present invention relates to a video signal reproducing device for reproducing video signals.

As one such video signal reproducing device, as shown in FIG. A rotating magnetic head 3 is in contact with the magnetic tape 2, and one field of video signals which are sequentially FM modulated is recorded as one track on the magnetic tape 2, and during reproduction, the magnetic head 3 sequentially scans this track. ing.

In such a rotating one-head type VTR, during playback, as shown in FIG. 2, the magnetic head 3 plays back the track Ta where the video signal of a certain field is recorded, and then plays back the track Ta where the video signal of the next field is recorded. Seam 4 must be scanned when switching tracks to reproduce track Tb.
Therefore, the signal corresponding to seam 4 is lost in the reproduced video signal, and noise is also generated. For this reason, generally there are four seams within the vertical blanking period of the video signal.
is designed to fit inside. FIG. 3A shows a vertical blanking period of, for example, an odd field of a known video signal, and signal waveforms before and after the vertical blanking period.

In the vertical blanking period, equalization pulses with a period of 0 and 5H (H is the horizontal period) exist before and after the vertical synchronization pulse (3H), and a horizontal synchronization pulse of more than 20 H is also included. . Now, if the seam 4 is made to exist after the vertical synchronization pulse, the reproduction signal from the magnetic head 3 will be
As shown in FIG. B, when the magnetic head 3 passes through the seam 4, the signal is lost for several hours. Therefore, when demodulating the reproduced FM modulated video signal, the third
As shown in FIG. C, not only is the horizontal synchronizing pulse within the vertical blanking period missing, but it is also inserted into the FM demodulation system, and the noise suppression effect of the mitter is lost, resulting in a large level of noise. Therefore, when a reproduced video signal is supplied to a monitor receiver, a phenomenon occurs in which the horizontal synchronization of the reproduced image is disturbed at the beginning of scanning and flicker occurs, resulting in a deterioration in the image quality of the reproduced image. The purpose of the present invention is to eliminate the adverse effects caused by the seam 4 described above, and by knowing the position of the seam 4 in advance,
Before and after the seam 4, a high-quality video signal is forcibly replaced with a reproduced video signal. Hereinafter, one embodiment of the present invention will be described with reference to FIG. supplied to

The signal obtained at the output terminal 8c of the switch circuit 7 is supplied to the buffer amplifier 9, and the output of the buffer amplifier 9 is FM.
The signal is supplied to the demodulator 10 and also to the other input terminal 8b of the switch circuit 7 via the 1H delay line 11.
A video signal is demodulated and obtained at the output terminal 12 of the FM demodulator 10. A vertical synchronization pulse is separated from this video signal by a vertical synchronization separation circuit 13, this vertical synchronization pulse is supplied to a pulse delay circuit 14, and its output is supplied to a pulse width setting circuit 15. A seam processing pulse is obtained, and the switch circuit 7 is controlled by this pulse.

Note that a monostable multivibrator can be used as the pulse delay circuit 14 and the pulse width setting circuit 15. That is, from the vertical synchronizing pulse Pv separated from the reproduced video signal shown in FIG. 5A, for example, 7.5H as shown in FIG.
A delayed pulse P, is formed in the pulse delay circuit 14, and a seam processing pulse P2 having a pulse width of, for example, 7H is formed in the pulse width setting circuit 15 as shown in FIG. The output terminal 8c of the switch circuit 7 is connected to the input terminal 8b only while P2 is occurring.

In the above configuration, if the reproduced signal shown in FIG. 3B is taken out from the magnetic head 3, the switch circuit 7 is switched by the seam processing pulse P2 as shown in FIG. 3D. 1 before it occurs
The reproduction signal for H is circulated through a loop consisting of the buffer amplifier 9, the 1H delay line 11, and the switch circuit 7 for 7H.

This circulating 1H video signal is of high quality,
Even if it is circulated through the 1H delay line 11 during 7H, there will be some jitter.
This is to the extent that it gets worse. Then, when the seam processing pulse P2 disappears, the output terminal 8c of the switch circuit 7 is connected to the input terminal 8a again. As described above, according to the present invention, the seam processing pulse P2 formed from the vertical synchronizing pulse Pv is generated at the position of the seam 4, and this pulse P2 converts the high quality q-determined image signal before 1H into the reproduced video signal at the seam 4. By replacing it with , the negative influence of the seam 4 can be removed.

However, according to the present invention, there is no need to provide a separate rotating magnetic head for seam compensation, and the structure of the apparatus is simple. Additionally, the present invention provides that the track is switched after the vertical sync pulse and the seam 4
It can be applied in exactly the same way not only to the case in which the vertical synchronization pulse arrives, but also to the case in which the seam 4 arrives before the vertical synchronization pulse as shown in FIGS. 3E and F.

In this case, the seam processing pulse P6 as shown in FIG.
can be formed from the previous vertical sync pulse. moreover,
If a 1H delay line of a dropout compensation circuit, which is generally provided in a VTR, is used, there is an advantage that it is not necessary to provide a 1H delay line only for seam compensation.

FIG. 6 shows an embodiment in this case, in which numeral 16 indicates a dropout detection circuit, the detection output of which is supplied to a waveform shaping circuit 17, and the output of the waveform shaping circuit 17 is supplied to an addition circuit 18Vc. The switch circuit 7 is controlled by the output of the circuit 18. Further, this adder circuit 18 is supplied with a seam processing pulse P2 formed in the same manner as in the previous embodiment. The seam compensation effect according to this other embodiment of the present invention is similar to that described above. Note that the seam processing pulse P2 may be formed from a position detection pulse synchronized with the rotational position of the magnetic head 3, in addition to the vertical synchronization pulse Pv separated from the reproduced video signal.

[Brief explanation of the drawing]

1 and 2 are configuration diagrams used to explain a video signal reproducing device to which the present invention can be applied, FIG. 3 is a waveform diagram used to explain the present invention, and FIG. 4 is a system diagram of an embodiment of the present invention. FIG. 5 is a waveform diagram used for the explanation, and FIG. 6 is a system diagram of another embodiment of the present invention. 1 is a guide drum, 2 is a magnetic tape, 3 is a rotating magnetic head, 4 is a seam, and 11 is a 1H delay line.

Claims (1)

[Scope of Claims] 1. A magnetic tape is run in a state where it is wrapped around the circumferential surface of the guide drum, and one rotating magnetic head is placed in contact with this magnetic tape to record an image. In a video signal reproducing device configured to reproduce a signal, when the magnetic head moves from one track to the next track, the reproduced signal of the joint is matched with the high-quality reproduced signal before the joint according to the joint. A video signal reproducing device that can be replaced during a predetermined period of time. 2 Automatically changes to 1 when a level change in the playback signal is detected.
When the magnetic head moves from one track to the next by supplying a seam processing pulse formed by anticipating the seam point to a dropout compensation circuit that inserts a signal before the horizontal period. 2. The video signal reproducing apparatus according to claim 1, wherein the reproduction signal of the seam is replaced with a high-quality reproduction signal before the seam for a predetermined period corresponding to the seam.