JPS6268382A - Compensating method for speed error in video signal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The invention relates to a method for compensating speed errors in a video signal.

When reproducing a video signal, such as a color television signal, from a prior art record carrier, the reproduction quality is as good as possible.
There are various errors in the signal that must be compensated for to a large extent. For example, various mechanical errors in the scanning device and the tape feeding device (tape running mechanism) cause variations in the time base (time axis) during recording and during reproduction. This time error, also called timebase error, occurs only at the end or beginning of each scan line, e.g. horizontally in the reproduced video signal, since no other suitable time markers are present in the video signal. It can be determined by comparing the phase of the synchronization pulse with that of a horizontal frequency comparison pulse. In the known time error compensator, the delay of the video signal is controlled according to the result of this measurement so as to compensate for the one hour error.

Similarly, in known digital time error compensators, video signals obtained by scanning a magnetic tape are written into a memory together with the clock pulses derived from these video signals and thus with the associated time errors; From this memory the video signal is read out with the clock pulses having time errors removed. Even in these time error compensators, the time error is measured only at the end or beginning of the scan line. However, various methods are known which make it possible to compensate for changes in time errors during the scanning of the respective scan line, so-called speed errors.

In these methods, used to compensate for time errors, the delay of the video signal is gradually changed toward the time error at the beginning of each scan line. For this purpose, known methods measure the time errors in successive horizontal blanking periods and compare them with one another.

The subsequent processing of the velocity error signal obtained from this comparison depends on the recording method used. The four magnetic heads sequentially write tracks on the tape surface, and these tracks are aligned with the edges of the tape. In magnetic tape devices using the almost perpendicular track method, and in the so-called segmented diagonal track method, scan lines are each scanned by the same head and each have the same position relative to the edge of the tape. A speed error compensator is used in which the speed error is averaged by means of an error signal over a plurality of revolutions of the spatula wheel. Mainly in connection with other diagonal track recording methods, the velocity error is determined for each one scan line, and the video signal is delayed by one scan line to transfer the error signal to the same scan line. It is known that it can be used.

PROBLEM TO BE SOLVED BY THE INVENTION Both known methods have drawbacks in the context of digital video processing devices such as magnetic tape devices operating with a segmented diagonal track recording method.

Effects of the Invention The method according to the present invention, which has the configuration described in the characteristic part of claim 1, has the following advantages over the first above-mentioned method:
It has the advantage that it is possible to compensate for speed errors during scanning in the first scan line of a so-called scan line package as well as during scanning in other scan lines. That is, detailed investigation shows that the time error when reproducing a video signal recorded by the segmented diagonal track method has a relatively low frequency component that extends over multiple revolutions of the head wheel. However, it has been found that the relative changes in the respective transitions from one segment to another remain approximately constant.

Compared to other known methods for compensating time errors, the method according to the invention has the advantage that the time errors can be determined simply and accurately. Despite being primarily used in magnetic tape devices that record fields in segments,
It is equally suitable for use in magnetic tape drives that record one field on each track.

Example An embodiment of the present invention will now be described in detail with reference to the drawings.

The diagram shown in FIG. 1 shows the speed error as a function of time for a magnetic tape device that performs segment scanning.

The curve shows the course of the velocity error during the scanning of four segments 1° 2.3.4. While each jump A or B occurs at the beginning of a segment, the change in velocity error is small within a segment of 52 scan lines. Segments 1 and 3 are reproduced by the first magnetic head 1, and segments 2 and 4 are reproduced by the second magnetic head.

It has been found that the jump in velocity error when passing from one head to another is approximately constant. However, the height of the speed error is generally subject to statistical fluctuations.

In the method according to the invention, the velocity error within a segment is determined starting from a scanning assumption in a known manner. However, for the modification of the first scanline, similar values from the previous scanline cannot be used, so
Jump change A or B from previous head change in the same direction
By using the height of , the value from the last scan line of one segment can be used to estimate the 15 positive values of the first scan line of the next segment.

In many embodiments, the values of jumps A and B are approximately the same, so that it is sufficient to estimate from one segment alternation the next. In a known magnetic tape device that performs segment scanning, no signal for determining the length of the last scanning line of each segment is generated at the end of the last scanning line during reproduction. Therefore, in the improvement of the method according to the invention, the speed error of the previous scan line is changed by the jump A
and B, and also for the velocity error of the first scan line of the next segment.

The method according to the invention will now be explained in more detail using numerical examples. Suppose we want to find the 1 positive value for the first scan line of segment 4. For this, the preceding segment 3
Similarly, in the 52nd scanning line, 1 measurement period for the 51st scanning line, which is used as each positive value, is added to itA. The quantity A is calculated as the difference between the value determined for the first scan line of segment 2 and the value determined for the 52nd scan line of segment 1, with the latter value being equal to the value determined for the first scan line. is derived from the length of the 51st scan line of the segment.

The system shown in FIG. 2 is run through a D-register 5 which is clocked by horizontal synchronization pulses.

The velocity error, approximately determined by measuring the scan line length, is sent out as a 9-bit wide digital signal. The horizontal sync pulse is set at the At the beginning of one scan line, the clock input of the D-register 5 is not supplied.

The digital signal indicating the proverbial value passes through an adder 6, which calculates the value A in each tenth scan line.
Or -B is added. A limiter 7 is connected to the adder 6, and the limiter 9 outputs a maximum value or a minimum value given by a 9-digit binary number when an overflow or underflow occurs due to addition in the adder 6. so that

An output 9 is connected to the limiter 7 via a register 8 clocked by horizontal frequency pulses, from which a correction signal is sent to a correction circuit known as 9M.

The output signal of the limiter 7 further records the correction value for the 52nd scan line of each segment until the next correction value obtained by measuring the length of the first scan line is provided. Another register 10 is supplied. From the register 10, the stored signal is taken in inverted form, so that
In adder 11 a difference of 14 positive values is formed between the first scan line of one segment and the last scan line of the preceding segment. These values A and B are stored separately in register 12.
and 13, respectively, for the duration of two segments, one in each case offset by one segment, and fed to the adder 6 at the beginning of the next segment.

Registers 12 and 13 are clocked by a horizontal frequency clock H. Their outputs are applied to registers 12 and 1 during scanning from the second to the 52nd scan line to the adder 6.
3 is controlled by the corresponding signals oc1 and oa2 via the OC input/output side, respectively, so that no signals are sent from the OC input/output sides.

As mentioned above, under certain preconditions, the values of signal jumps A and B may be approximately the same, in which case the registers 12 and 13 are the same as the circuit for implementing the method of the invention. Only the main circuit elements of the device are shown. The manner in which clock signals and switching signals are supplied to the circuit elements is also briefly shown. Thus, for example, the horizontal frequency pulses designated H can have different widths and phases.

[Brief explanation of drawings]

FIG. 1 is a voltage one-hour diagram showing an example of the course of speed error. FIG. 2 is a block circuit diagram of an apparatus for carrying out the method of the invention. 1.2.3.4... Segment, 5... D-register, 6... Adder, γ... Limiter, 8... Register, 9... Output side, 10...・Register, 11...
Adder, 12.13...Register FIG, 1

Claims (1)

[Claims] 1. A method for scanning a record carrier and compensating for speed errors in a video signal recorded on a plurality of tracks running diagonally in the longitudinal direction of the record carrier, comprising: , a first error signal corresponding to the velocity error is determined and used to compensate for the velocity error of each subsequent scan line, and a second error signal is determined for compensating the velocity error of each first scan line of one track. 1. A method for compensating velocity errors in a video signal, characterized in that an error signal of is determined at the beginning of each track and used to compensate for velocity errors in the next or subsequent tracks. 2. A plurality of tracks (segments) in which signals, each belonging to one field, are sequentially scanned by a plurality of magnetic heads attached to the periphery of one head ring.
A method for compensating speed errors in a video signal as claimed in claim 1, as recorded by. 3. forming a second error signal the difference between the first error signal for the first scan line of each segment and the first error signal for the last scan line of the respective preceding segment; A method for compensating for speed errors in a video signal according to claim 2. 4. A method for compensating for velocity errors in a video signal as claimed in claim 3, in which the first error signal for the previous last scan line of each segment is used for forming the difference. 5. For the modification of the first scanline of each segment, the first of the last scanline of the respective preceding segment.
4. A device for compensating for speed errors in a video signal as claimed in claim 3, wherein a second error signal from each preceding or immediately preceding segment is added to the error signal of each of the first and last segments. 6. forming a second error signal the difference between the first error signal for the first scan line of each track and the first error signal for the last scan line of the respective preceding track; A device for compensating speed errors in a video signal as claimed in claim 1, obtained by: 7. For modification of each first scan line of the track,
7. A video recording medium according to claim 6, wherein a second error signal from each preceding track or one preceding track is added to the first error signal of the last scan line of each preceding track. A method of compensating for velocity errors in a signal.