JPS61218282A - Inserting circuit for video tape recorder - Google Patents

Abstract

PURPOSE:To superimpose only by characters by providing a signal comparing means that outputs a clamping signal only when it is over a reference level and providing a signal clamping means that clamps to a regulated level and outputs a reproducing video signal only when the clamping signal is inputted. CONSTITUTION:The reproducing signal of the video track of a channel B is inputted to a reproducing circuit 7 and the reproducing signal that reproduces the PCM track of a channel A is inputted to a luminance signal processing circuit 8. Also, when a clamp pulse 200 is inputted to a clamping circuit 9, the clamping circuit 9 outputs a signal that an input video signal 100 is clamped at a regulated level as an output video signal 300. An insert video signal that is recorded on the PCM track of the tape is demodulated and only when the level of a returned luminance signal VIN over a prescribed level is detected, the video signal 100 which is reproduced from the video track of the tape is outputted as the signal that is clamped at the regulated level. Thus, only white characters are superimposed on a screen with the reproducing signal from the video track by corresponding the insert video signal with the characters.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an insert circuit for a video tape recorder (VTR).

[Technical background of the invention]

In the so-called 8 m VTR, which uses 8 mm wide tape, the tape is wrapped around the cylinder at an angle of 180 degrees or more.
The 180 degree portion is a video area (video track), the portion within the winding beyond that is a PCM (phase change m) area (PCM track), and an audio signal converted into VCPCM can be recorded in this portion. By the way, if you want to insert a part of the video into a tape with a video signal recorded in the video area of the tape mentioned above, you can record the video signal of the video you want to insert again into the video area (record it, or erase it and then record it). This is done on a monthly basis.

[Problems with background technology]

However, the above-mentioned insert method had a drawback in that the screen was completely replaced and, for example, it was not possible to superimpose only subtitles on the screen.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, it is an object of the present invention to provide an insert circuit for a video tape recorder that allows only characters to be superimposed on the screen.

[Summary of the invention]

In a video tape recorder in which a PCM track is formed as an extension of a video track, the present invention provides means for recording a signal to be inserted into the PCM track as a video signal, and a means for recording a first playback signal obtained by playing back the video track. a first reproduction circuit that generates a reproduced video signal by inputting the input signal and subjecting it to luminance signal processing and color signal processing;
Extract and restore the luminance signal from the second reproduced signal obtained by reproducing the PCM trap! ! 4 brightness (2nd to produce 1st
a reproducing circuit, a signal comparison means for comparing the demodulated luminance signal inputted from the second reproducing circuit with a reference level, and outputting a clamp signal only when the demodulated luminance signal is equal to or higher than the reference level;
A signal clamp means is provided for inputting the reproduced video signal output from the reproduction circuit and outputting it normally, but clamping the reproduced video signal to a constant level and outputting it only when the clamp signal is input. By doing so, the above objective is achieved.

(Embodiment of the invention) An embodiment of the invention will be described below with reference to the drawings.Cylinder 1
The figure is a block diagram showing an embodiment of an insert circuit for a VTR according to the present invention. Video head 1 is channel /I/
A is played back, and video head 2 plays back channel B. Reproduction signals reproduced by video heads 1 and 2 are independently amplified by reproduction amplifiers 3 and 4, respectively, and then input to movable terminals C of switches 5 and 6. These switches 5.6 are switched by head switching pulses 400. Terminal H of switch 5.6
The signal obtained from the terminal of the switch 5.6 is input to the reproducing circuit (@1 reproducing circuit) 7, and the signal obtained from the terminal of the switch 5.6 is input to the luminance signal processing circuit (fourth reproducing circuit) 8. The reproduced signal input to the reproduction circuit 7 is processed by a luminance signal processing section 71 and a color signal processing section 72, and these processed signals are further added by an adder 73 to produce a reproduced video signal 10.
0, p, which is output to the crank circuit 9. The reproduced signal input to the luminance signal processing circuit 8 now contains only the demodulated luminance signal component, and this is 01! The signal VAN is input to the signal level comparator 10Vc. Note that this signal level comparator 1
0, the reference voltage v1 is applied. The signal level comparator IO outputs a clamp pulse 200 to the crank circuit 9 as a result of comparing the input signal and the reference signal. The R2 amplifier circuit 9 normally passes the reproduced video signal Zoo output from the reproducing circuit 1 to the next stage as it is as the output video signal 300, but when the R2 amplifier pulse 20G is input, the input video signal Zoo is kept at a certain level. This clamped signal is output as an output video signal 300.

Next, the operation of this embodiment will be explained with reference to the switching timing chart of the switches 5 and 6 shown in FIG.

When the head switching pulse 400 is at a high level, the switch 5 is switched to the H side and the switch 6 is switched to the L side. Also, at this time, the head 1 is reproducing the video signal of the video track of the A channel, and the head 2 is playing the PCMo of the B channel (no signal during the remaining period). Therefore, the reproduction circuit 7Vc receives the reproduction signal of the video track of the A channel (the first reproduction signal), and the luminance signal processing circuit 8 receives the reproduction signal of the PCM track of the B channel (the second reproduction signal) for a predetermined period. is input.

The luminance signal processing circuit 8 extracts a luminance signal from the input reproduced signal, demodulates it to obtain a demodulated luminance signal VIN, and inputs this to the signal level comparator IO. - 10,000, the reproduction signal input to the reproduction circuit 7 is converted into a video signal by the luminance signal processing section 71 and the color signal processing section 72, and this video signal Zo
o is input to the clamp circuit 9. Signal level comparator 1
0 is the input demodulated luminance signal VIN and reference level VII
When Vx*)VampO, a clamp pulse of 200 is output to the clamp circuit 9. Clamp circuit 9
When the clamp pulse 200 is not input, the input video signal 100 is output as is as the output video signal 300, and when the clamp pulse 200 is input, the input video signal 4i is set to a certain level (for example, the white level of the video signal). ) is output as an output video (No.N 300).Next, when the switching pulse 400 becomes low level, the switch 5 is switched to the terminal LOW side and the switch 6 is switched to the terminal H side. The video track of the B channel is played back, and the heptl plays the PCM track of the A channel for a predetermined period of time. Therefore, the playback key signal (first playback signal) of the B channel video track is input to the playback circuit 7. , the luminance signal processing circuit 8 has A
The playback signal that played back the PCM track of the channel (second
playback signal) is input. Other operation lines The operation is exactly the same as that described above, and when the clamp pulse 200 is input to the second ring j89, the clamp circuit 89 receives the input video signal Zoo
The output video signal 30 is a signal clamped to a constant level.
Output as 0.

According to this embodiment, an insert video signal recorded on a PCM track of a tape is demodulated, and a demodulated I! 14 only when the luminance signal vtrt is detected,
The video signal played from the video track of the tape is output as signal 30.
0 to a certain level (white level) K/? In order to output it as a sampled signal, if you associate the insert video signal with the text (for example, when you sweep white text on paper with a dark background), the screen will be output as a video signal played back from the video track. It is possible to superimpose only the

〔Effect of the invention〕

As described above, according to the insert circuit of the video tape recorder of the present invention, the video signal of the video recorder and the P
The video signal of the CM track is reproduced separately, and when the demodulated luminance signal of the video signal reproduced from the PCM track is above a predetermined level, the video signal reproduced from the video track is output as a signal clamped to a constant level. In particular, it has the effect of superimposing only a small amount of text on the screen.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an insert circuit of a video tape recorder according to the present invention. FIG. 2 is a switching timing chart of the switch shown in FIG. 1.2... Head 5.6 - Switch 7 - Reproduction circuit 8 - Luminance signal processing circuit 9 - Clamp circuit 1 G
---Signal level comparator representative Patent attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2 Switch + 6

Claims (1)

[Claims] In a video tape recorder in which a PCM track is formed as an extension of a video track, the first playback signal obtained by playing back the video track is input and subjected to luminance signal processing and color signal processing to generate a playback video signal. a first reproducing circuit that generates a demodulated luminance signal, a second reproducing circuit that extracts a luminance signal from a second reproduced signal obtained by reproducing a PCM track, and generates a demodulated luminance signal; signal comparison means for comparing the demodulated luminance signal with a reference level and outputting a clamp signal only when the demodulated luminance signal is equal to or higher than the reference level; 1. An insert circuit for a video tape recorder, comprising signal clamping means for clamping an input reproduced video signal to a constant level and outputting the same only when the clamp signal is input.