FR2587867A1 - METHOD FOR COMPENSATING FOR SPEED ERRORS IN VIDEO SIGNALS - Google Patents

Abstract

A.PROCEDE FOR COMPENSATING SPEED ERRORS IN VIDEO SIGNALS. B. PROCESS CHARACTERIZED IN THAT FIRST ERROR SIGNALS, CORRESPONDING TO SPEED ERRORS, ARE DETECTED PER LINE AND ARE USED TO COMPENSATE THE SPEED ERRORS OF THE RESPECTIVE FOLLOWING LINE, WHILE COMPENSATION FOR SPEED ERRORS OF THE RESPECTIVE FIRST LINE OF A TRACK, SECOND ERROR SIGNALS ARE DETECTED AT THE BEGINNING OF THE TRACK UNDER CONSIDERED AND ARE USED TO COMPENSATE THE SPEED ERRORS OF THE FIRST LINE OF THE IMMEDIATELY NEXT TRACK OR OF THE TRACK COMING IMMEDIATELY AFTER. C. THE INVENTION RELATES TO METHODS FOR COMPENSATING FOR SPEED ERRORS IN VIDEO SIGNALS.

Description

1.a- "Method for compensating for speed errors in

video signals ".

________________

  The invention relates to a method for compensating

  speed errors in video signals taken from a recording medium, preferably a

  magnetic tape, and recorded on several tracks

  obliquely in relation to the longitudinal extension

of this recording medium.

  When reproducing video signals, including color television signals, from

  of a recording medium, various defects appear-

  in the signals, which must be compensated to a large extent for

  as good as possible. In particular, because of different

  mechanical precisions of the scanning device and the

  positive for the transport of the band, fluc-

  of the time base during playback in relation to the time base during the recording. These time errors, also called time base errors, can not be, in the absence of other appropriate time references in the video signal, measured at the end or at the beginning of each of the lines, for example

  by a phase comparison of the synchronization pulses

  Horizon frequency frequency of the reproduced video signal 2.-

  with horizontal frequency comparison pulses

  tale. In the known time error compensators,

  a delay of the video signals is controlled according to the result.

  state of this measure in the sense of compensation for time errors. -

  In digital compensators

  known errors of time, the video signals

  surveyed from a magnetic tape are entered,

  with synchronization pulses derived from

  video signals, and also time error-related, in a memory from which they are read with timing pulses which are free from time errors. Even in these time error comparators, time errors can only be measured at the beginning or at the end of the lines. However, to compensate for changes in time errors

  during a line, modification called speed error

  se, different processes are known. In these processes,

  the delay of video signals used to compensate for

  time, is gradually modified during the

  each of the lines in the direction of the er-

  time to wait at the beginning of the next line.

  For this purpose, in known methods, time errors are measured in the suppression intervals

  horizontally successive and compared with each other.

  The subsequent processing of error signals

  speed data obtained by this comparison, is adjusted according to the recording method used. In the case of magnetic tape apparatus, according to the method,

  transversal tracks in which four magnetic heads

  ticks successively register on the strip tracks that are located almost perpendicular to the edge of the strip, and in the case of so-called processes

  segmented oblique tracks, compensations are

  speed errors in which the average of the 3.-

  speed defects of the lines which are scanned respectively

  by the same head and which have respectively the same position relative to the edge of the magnetic strip, these are

  established on several revolutions of the heads wheel. spring

  cipally correlated with other oblique track recording methods, it is known to detect the speed errors for one line respectively and to delay the video signals of a line, so that

  the error signal can be used for the same line.

  Including in correlation with a digital video processor for a magnetic tape apparatus that operates according to the segmented recording method

  on oblique tracks, the known methods have disadvantages

vantages.

  To remedy these drawbacks, the

  The invention provides a method characterized in that first error signals, corresponding to the speed errors, are detected per line and used for

  compensate for the speed errors of the respective line

  next, while for the compensation of speed errors of the respective first line of a track, second error signals are detected at the beginning of the track in question and are used to compensate for

  speed errors of the first line of the immediate runway

  next or from the next. The method according to the invention with the characteristics defined above has, with respect to the above-mentioned first method, the advantage that both the speed errors during the first line of what is called a packet of lines and during also

  the other lines can be compensated advantageously

  is lying. In particular, it proved to be very

  accurate, that time errors during reproduction

  In the case of video signals recorded according to the method of the segmented oblique tracks, there is a relatively low frequency component which extends over several head revolutions, but the relative changes during the transition from one segment to the other. , then remain in practice constant. Compared with other known methods for time error compensation, the method according to the invention has the advantage that simple and accurate detection of time errors is possible. Although it is mainly intended for use in the case

  of magnetic tape devices with a seg-

  frames, use with magnetic stripe devices which respectively record a frame

  on a track, can also be advantageous.

  Other features of the invention make it possible to envisage advantageous supplements and

  improvements of the process defined above.

  According to a characteristic of the invention, the signals forming respectively part of a frame are recorded on several tracks (segments) which are scanned successively by several magnetic heads arranged

  on the periphery of a wheel of heads.

  According to another characteristic of the invention

  the second error signal is obtained by forming the difference between the first error signals for the first line of a segment and for the last

line of previous segments.

  According to yet another characteristic of

  the invention, the first error signal for the front

  line of a segment, is used for training

of the difference.

  According to another characteristic of the invention

  to correct the first line of a segment, the se-

  cond error signal from the preceding or preceding segment is added to the first signal 5.-

  of the last line of the previous segment.

  According to another characteristic of the invention

  tion, the second error signal is obtained by forming the difference between the first error signals for the first line of a track and for the last line

from the previous track.

  Finally, according to another characteristic of the invention, to correct the first line of a track,

  the second error signal from the pre-existing track

  cedente or the one preceding it, is added to the first

  first error signal from the last line of the pre-

  cedente. An exemplary embodiment of the invention is shown in the accompanying drawings and will be shown

  in more detail in the description below.

  FIG. 1 is a diagram of the voltage as a function of time as an example for a possible presentation of speed error, FIG. 2 is a block diagram of a device for carrying out the method according to FIG. invention. The diagram shown in FIG. 1 shows speed versus time errors as an example of a magnetic stripe apparatus with segmented scanning. The curve represents the evolution of errors

  speed during the scanning of 4 segments 1, 2, 3 and 4.

  At the beginning of each segment, there is a sharp variation A or B, while the speed error inside

  a segment consisting of 52 lines changes only slightly.

  Segments 1 and 3 are reproduced by a first magnetic head, while segments 2 and 4 are reproduced

by a second magnetic head.

  It then became clear that sudden variations

  of the speed error when moving from one head to the other, remain in practice constant. The level of 6.- the speed error as a whole is however subject

  among other things, statistical fluctuations.

  In the process according to the invention, it is assumed that, within a segment, a speed error is detected in a manner known in itself by measuring the length of a line and can be used

  for correction in the next line. As though

  For the correction of the first line, there is no analogous value available from a preceding line, the height of the abrupt change A or B of the change of head of the same preceding direction.

  is used to be able, with the help of the ex-

  deals with the last line of one of the segments, shoot

  conclusions as to the value of correcting

  for the first line of the next second segment.

  In many cases of application, the values of the abrupt variations A and B are almost identical, so that it suffices to draw conclusions from one segment change to the next. In known magnetic stripe devices with segmented scanning, there is then no reproduction after the last line of a

  segment of available signal to determine the length of

  this line. Consequently, in a complement of the method according to the invention, the speed error of the penultimate line is used for the determination of sudden variations A and B as well as for the error

  speed of the first line of the next segment.

  The process according to the invention will be further described in a little more detail below with the aid of a

  digital example. A correction value must be

  terminated for the first line of segment 4. For this purpose, the value measured for the fifty-first line of the preceding segment 3, which is used in the fifty-second line also as a correction value, is added to the quantity A. A is calculated from 7.- the difference of the values determined for the first

  line of segment 2 and the fifty-second line of the seg-

  1, this last value being derived from the length

  of the fifty-first line of the first segment.

  The device according to FIG. 2 is applied by means of a register D 5 synchronized by a pulse of horizontal frequency, the speed errors determined essentially by the measurement of the

  line lengths and put in the form of digital

  range of 9 binary digits. For the value determined at the end of the fifty-first line

  not only available for correction

  in the fifty-second line, but also for the determination of sudden variations A or B, the impulse

  N is not applied to the synchronization input of the re-

  D5 at the beginning of the first line.

  The digital signals representing the

  their correction through a totalizer 6 thanks to-

  which only in the first lines, the values A or B are added. At totalizer 6, connects

  a limiter 7 which guarantees that the maximum or minimum value

  given by the 9-digit binary number, is transmitted

  put when due to the addition in the totalizer 6,

  there would be a surplus or a disability.

  At the limiter 7 is connected, via

  of a register 8, which is synchronized with

  horizontal frequency pulses, the output 9 from which the correction signals can be applied

  to correction circuits known per se.

  The output signals of the limiter 7 are in

  addition, applied to another register 10 which stores the value

  their correction for the fifty-second line of each segment until the next correction value obtained by measuring the length of the first line. The signals thus sotcked are taken from the register 10 in the inverted form, from

  so that in the totalizer 11 the difference in

  their correction of the first line of a segment and

  from the last line of the previous segment, is formed.

  These values A and B are separately stored in the registers 12 and 13, respectively for the duration of two segments and, when shifted by one segment, applied

  respectively at the beginning of the next second segment

user 6.

  Registers 12 and 13 are synchronized

  with a pulse H of horizontal frequency. Leu, sor

  are respectively controlled via an input OC with appropriate signals 001 and 002, so that no signal is applied to the totalizer 6

  from registers 12 and 13 during the second jus-

than at the fifty-second line.

  As already mentioned above, the values of the abrupt changes A and B of the signal can be practically mimics under these determined conditions

  and in this case, only one of the registers 12 or 13 is sufficient.

  To facilitate understanding of the invention

  2, the essential constituent groups of a circuit device for carrying out the method according to FIG.

  the invention. Similarly, the nutrition of the groups

  with synchronization signals and signals

  switching has been shown in a simplified way.

  Thus, for example, the horizontal frequency pulses designated by H may include expanses

  and quite different phase positions.

9._

Claims (7)

CLAIMS R E V E N D I C A T I 0 N 8   1.- Method for compensating for speed errors in video signals taken from a   recording medium, preferably a magnetic tape   tick, and recorded on several tracks extending obliquely with respect to the longitudinal extension of this recording medium, characterized in that first error signals, corresponding to the   speed errors, are detected per line and are used   to compensate for the speed errors of the   next, while for the compensation of the speed errors of the respective first line of a track, second error signals are detected at   beginning of the track in question and are used to   think the speed mistakes of the first line of the   immediately following one or the one immediately mediately after.   2. A process according to claim 1,   characterized in that the signals forming respectively part of a frame are recorded on several tracks (segments) which are successively scanned by several magnetic heads disposed at the periphery of a wheel heads.   3. Process according to claim 2,   characterized in that the second error signal is obtained by forming the difference between the first error signals for the first line of a segment and for the   last line of previous segments.   4. Process according to claim 3,   characterized in that the first error signal for the front   last line of a segment is used for difference.   5. A process according to claim 3, characterized   in that, to correct the first line of a segment, the second error signal from the segment 10.-   precedent or precedent is added to the first   first error signal from the last line of the pre- yield.   6. A process according to claim 1, characterized   characterized in that the second error signal is obtained by forming the difference between the first error signals for the first line of a track and for the   last line of the previous track.   7. A process according to claim 6, characterized   in that in order to correct the first line of a track, the second error signal from the preceding or preceding track is added to the first error signal of the last line of the previous track.