JPH04346588A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To execute skew correction and color sequence correction with simple configuration at the VTR of a VHS-PAL system or the like without using any 0.25H delay lines. CONSTITUTION:The time delay of 0.75H, 0.5H and 0.25H is required continuing horizontal synchronizing signals and concerning the 0.25H delay, however, the delay time of 1/25H is obtained by serially connecting a 0.5H delay line 7 and a 0.75H delay line 9. Further, by separately using a 1H delay line 5, the delay time of 0.25H as the difference is realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit for a video tape recorder at a playback speed different from that during recording.

0002

2. Description of the Related Art In the LP (long time) mode of a VHS-PAL VTR (video tape recorder), the deviation amount αH between adjacent tracks in a recording track on a tape is equal to 0.75H (H is a horizontal (corresponds to the period of the synchronization signal). When performing field still playback using the main head and sub-head (reverse azimuth) shifted by 2H from 180 degrees on a tape recorded in such a format, the horizontal synchronization signal changes at the switching point of each field. A discontinuity of 0.25H occurs. As a result, skew distortion and color fading phenomena occur on the playback screen.

Therefore, in the past, 0.25H (glass delay line) and 0.5H (CCD delay line) were used to
By sequentially applying delays of 5H, 0.5H, 0.25H, and 0H to the reproduced signal, discontinuity in the horizontal synchronization signal is prevented from occurring.

Next, the above operation will be explained based on FIG. FIG. 3 is an explanatory diagram showing the sequence of the horizontal synchronization signal and color signal of the video signal to be reproduced. A shows the signal as it is being reproduced. When field still playback is performed, there are 313.25 horizontal synchronization signals included in the head switching period. Therefore, when using a main head and a sub-head that are provided 2H apart from each other by 180 degrees, a deviation of 0.25H occurs. That is, the signal of the next field is delayed by 0.25H (leads by 0.75H) with respect to the expected phase. Note that * is added to indicate the color signal sequence; in this example, it is a PAL signal, so during the period marked *, for example, the RY component is in a negative state with respect to the u axis. It is shown that.

[0005] B is sequentially 0.75H for the signal A.
, 0.5H, 0.25H, and 0H are shown. At timing a, there is a deviation of 0.25H as shown in b, so here, 0.75H.
By providing a delay time of H, the horizontal synchronization signal is continuous. At the next timing b, 0.75 at timing a
Since a delay of H is given, a lead of 0.5H occurs, so the horizontal synchronization signal can be made continuous by giving a delay time of 0.5H.

At the next timing c, 0 at timing b
．． Since a delay of 5H is given, an advance of 0.25H has occurred. Therefore, by providing a delay of 0.25H, the horizontal synchronization signal can be made continuous. At the next timing d, since a delay of 0.25H was given at timing c, there is no deviation, so the necessary delay amount is 0H.

By changing the delay time in this way,
Horizontal synchronization signals can be made continuous. However, as is clear from (b), the color signal sequence remains deviated. Therefore, in (b), by further providing a delay time of 1H to the periods indicated by A and B, the sequence of color signals can be made continuous.

[0008] Regarding skew correction, for example,
This is disclosed in Japanese Patent Application Laid-Open No. 55-33316 (H04N5/93).

[0009]

However, although the above method uses 0.25H and 0.75H delay lines, only the glass delay line can be used for the 0.25H delay line. The circuit scale becomes large. This is because the passband of the glass delay line is narrow, and when trying to pass a video signal, the frequency range from 13MHz to 18MHz
This is because it must be converted into a signal. On the other hand, with a delay line using a CCD, this is not necessary because the band is wide.

0010

[Means for solving the problem] In the present invention, 0.75H
A delay time of 1.25H is created using a 0.5H delay line and a 0.5H delay line, and by using this, the 0.25H delay line is unnecessary. That is, 1.25H
By using the delayed signal and the 1H delayed signal, the relative amount of delay is 0.25H.

[0011]

[Function] Since a 0.25H delay line is not used, there is no need to use a glass delay line, a frequency conversion circuit or a modulation circuit, etc. are not required, and the configuration can be simplified.

0012

[Embodiment] An embodiment will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment, and FIG. 2 is an explanatory diagram showing the operation of the embodiment.

Of the reproduced video signals, the luminance signal is input from terminal 1, and the color signal is input from terminal 2. 4 is a circuit for controlling the color signal sequence;
Correct discontinuities in color signals. The input luminance signal and color signal are mixed in a mixing circuit 3 and then supplied to a 1H/CCD delay circuit 5 and a first changeover switch 6. Therefore, the first
The changeover switch 6 controls whether or not to give a 1H delay to the video signal.

The output of the first changeover switch 6 is applied to a second changeover switch 8, a 0.5H CCD delay line 7, and a fifth changeover switch 12. The second changeover switch 8 selects the output of the first changeover switch and the output of the 0.5H CCD delay line 7. The output of the second changeover switch 8 is 0.75H・
After being delayed by the CCD delay line 9, the third changeover switch 10
given to. The third changeover switch 10 has this 0.75
Select H・CCD delay line 9 output and 0.5H・CCD delay line 7 output.

The fourth changeover switch 11 selects the output of the third changeover switch 10 and the output of the 0.75H CCD delay line 9. The output is the other input of the fifth changeover switch. A control circuit 14 controls the first to fifth changeover switches. In each changeover switch circuit, when the control pulse from the control circuit is at L level, the terminal on the black circle side is selected. The control circuit 14 also controls the color sequence control circuit 4.

Next, the operation will be explained with reference to FIG. A in Figure 2 is a VTR of VHS-PAL system, same as A in Figure 3.
This shows a signal during field still playback in LP mode. As described above, in this signal, there is a discontinuity in the horizontal synchronizing signal at the joint of one field, and a discontinuity in the sequence of the color signal also occurs. Further, F to N are control pulses from the control circuit.

The signal B in FIG. 2 is the signal A delayed by 1H, and represents the signal that has passed through the 1H CCD delay line 5. C shows the signal at the terminal 13, when only the succession of horizontal synchronizing signals is considered.

In the first field in FIG.
The first changeover switch 6 selects the black circle side, the second changeover switch 8 and the third changeover switch 10 select the black circle side, the fourth changeover switch 11 selects the black circle side, and the fifth changeover switch 12 selects the white circle side. Therefore, on the output terminal 13, a reproduced signal delayed by 1H is generated. In the next field, select the first changeover switch 6 to the black circle side, the second changeover switch 8, the third changeover switch 10 to the black circle side, the fourth changeover switch 11 to the white circle side, and the fifth changeover switch 12 to the black circle side. There is. In other words,
The output of the first changeover switch 7 is the output of the second changeover switch 8, 0.
．． In order to appear at the terminal 13 via the 75H CCD delay line 9, a delay time of 0.75H is given. Therefore, the horizontal synchronization signal at point e is continuous.

In the next field, the first changeover switch 6
is the black circle side, the second changeover switch 8, the third changeover switch 10
, the fourth changeover switch 11 selects the black circle side, and the fifth changeover switch 12 selects the black circle side. That is, the output of the first changeover switch 6 passes through the 0.5H CCD delay line 7 and appears at the terminal 13. The second field is 0.
This eliminates the 0.5H shift at point f caused by the 75H delay.

In the next field, the first changeover switch 6
is white circle side, second changeover switch 8, third changeover switch 10
, the fourth changeover switch 11 selects the white circle side, and the fifth changeover switch 12 selects the black circle side. In other words, 1H・C
The 1H delay by the CD delay line is not performed, and the output of the mixing circuit 3 is given a delay time of 1.25H by the 0.5H delay line 7 and the 0.75H delay line 9. In the previous field, the delay time of 1H + 0.5H was essentially given, so the 0.25H deviation that occurs due to this is canceled by the difference between the 1.5H delay and the 1.25H delay. Ru. Therefore, the horizontal synchronization signal is continuous at point g.

Although the continuity of the horizontal synchronizing signal can be maintained by the above operations, the discontinuity of the color signal sequence is not eliminated. That is, in periods D and E, the sequence of color signals is reversed. To undo this,
Correction is performed using a control pulse such as nu. For example, the color signal correction circuit 4 is configured to delay the color signal by 1H when the control pulse 4 is at H level. By this processing, as shown in E, it is possible to make the horizontal synchronization signal continuous and the color signal sequence continuous during field still playback. The actual processing output is expressed here.

[0022] Care must be taken with the timing of the control pulses, except for the control pulse shown in Fig. 2, in relation to the vertical synchronization signal of the original video signal (A in Fig.
It must be delayed by 1H.

Note that a 0.75H delay line can be realized by multiplying the clock frequency of a CCD delay line with a wide variable range for TBC (time base collector) by 4/3 using a 1H delay line. . Therefore, the only types of delay lines that are actually required are 0.5H and 1H delay lines.

[0024]

[Effects of the Invention] As described above, in the present invention, 0.2
Since skew correction in the LP mode of the VHS-PAL system can be realized without using a 5H delay line, the configuration is simplified and the effect is great.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment.

FIG. 2 is an explanatory diagram showing the operation of the embodiment.

FIG. 3 is an explanatory diagram showing the operation of a conventional example.

[Explanation of symbols]

4 Color signal correction circuit 5 1H・CCD delay circuit 6 First selector switch 7 0.5H・CCD delay line 8 Second selector switch 9 0.75H・CCD delay line 10 3rd selector switch 11 4th changeover switch 12 5th changeover switch

Claims (1)

[Claims] Claim 1. A video signal processing circuit that processes a video signal in which a discontinuity of at least 0.25H exists in a horizontal synchronizing signal at a joint between fields.
corresponds to the period of the horizontal synchronizing signal), and a delay means of 0.
5H delay means, 0.75H delay means, and this 0.75H delay means.
A means for obtaining a delay time of 1.25H by connecting a 5H delay means and a 0.75H delay means in a subordinate manner, and a means for obtaining a delay time of 1.25H with the 1H delay means and a means for obtaining a delay time of 1.25H are used to produce an image. A video signal processing circuit comprising: switch means for giving a signal a delay time of 0.25H.