GB2126831A

GB2126831A - Method of and apparatus for phase compensation for still picture and slow motion functions in video equipment

Info

Publication number: GB2126831A
Application number: GB08323245A
Authority: GB
Inventors: Reinhard Schulein
Original assignee: Grundig EMV Elektromechanische Versuchsanstalt Max Grundig GmbH
Current assignee: Grundig EMV Elektromechanische Versuchsanstalt Max Grundig GmbH
Priority date: 1982-09-04
Filing date: 1983-08-30
Publication date: 1984-03-28
Also published as: DE3232886A1; DE3232886C2; FR2532804A1; GB2126831B; GB8323245D0; FR2532804B1

Abstract

A method of and apparatus for compensating the phase modulation of the vertical sync pulse during the auxiliary functions of still picture and slow motion in video recording and/or reproduction equipment, without using a delay line. This is achieved in that an artificial vertical sync pulse is used which alters appropriately and compensates the phase jump. Depending on the video system, the invention can be embodied in a simple manner according to the track displacement specific to the system and the switching over of the video heads for the auxiliary functions, the position of the artificial vertical sync pulse being switched over alternately and adapted to the particular system. A microcomputer may be provided in a particularly advantageous and simplifying manner for the production of the alternating artificial vertical sync pulses and at the same time also renders possible the production of a key-in pulse, the production of the video-head switching pulses, a drop- out recognition and a time-lapse operation. <IMAGE>

Description

SPECIFICATION Method of and apparatus for phase compensation for still picture and slow motion functions in video equipment This invention relates to a method of and apparatus for compensating the phase modulation of the vertical sync pulse for the auxiliary functions of still picture and slow motion in video recording and reproduction equipment.

Apart from the standard functions, such as recording, reproduction, high speed, video recording and reproduction equipment which is extended in its technical functions, also comprises auxiliary functions such as slow-motion, timelapse and still picture. During the still-picture and slow-motion reproduction, errors in vertical synchronisation may occur as a result of the fact that during still-picture reproduction, one video head, for example of a video recorder, or, during slow-motion reproduction, at times both video heads sink too early into the magnetic tape used, because of the altered tape speed in comparison with the recording, and the vertical sync pulse present on the magnetic tape is read correspondingly earlier.The difference in time of the vertical sync pulses between two fields is then so great that a jump of the picture in the vertical direction is to be seen on the television screen. In order to compensate for this synchronisation error which occurs, it is known to provide a delay module with a delay network consisting of an amplifier, an analogue switch and a glass delay line. In this case, the glass delay line delays the FM signal read from the tape by one line. The corrected FM signal is supplied to the luminance circuit of the video equipment for further processing (GRUNDIG Technische Informationen, No. 6/1980, pages 290 to 292).

The keying in of an artificial vertical sync pulse is also known, for example, from GRUNDIG Technische Informationen, No. 3/1970, page 804.

We have now devised a system to compensate the phase delay distortion occurring in video recording and reproduction equipment, without using a delay line.

In accordance with this invention, there is provided a method of or apparatus for compensating the phase modulation of the vertical sync pulse for the auxiliary functions of still picture and slow-motion in video recording and/or reproduction equipment, wherein an appropriate artificial vertical sync pulse is used which compensates the phase modulation.

With the method and apparatus according to the invention, the phase modulation of the vertical syric pulse occurring through the track displacement in the case of a still picture and slow motion is compensating by using an alternating artificial vertical sync pulse according to the invention, in a simple manner. In order to avoid faulty synchronisation of the television receiver connected to the video equipment, the composite synchronisation signal of the television signal may advantageously be blanked out by a key-in pulse, which preferably lies in the "black region", from the moment of the change-over of the video head to the artifical vertical sync pulse.Depending on the video recording and reproduction system, the method according to the invention can be used in a simple manner, according to the switching over of the video heads specific to the system and the track displacement for the still-picture function and slow-motion function specific to the system, the position of the artificial vertical sync pulse being switched over alternately and adapted to the particular system. A sequential network or a microcomputer may be produced to produce the alternating artificial vertical sync pulses. In this case, it proves advantageous and simplifying for the microcomputer to be provided not only for the production of the artificial vertical sync pulse and supplying it to the luminance signal circuit of the video recorder, but also, at the same time, for producing the key-in pulse and the production of the switching pulses for the video head.In addition, the microcomputer may be provided for time-lapse operation and drop-out scanning.

The invention is explained in more detail below, by way of example, with reference to the Figures of the drawing.

Figure 1 shows a diagrammatic illustration of the phase modulation during the auxiliary functions still picture and slow motion in conjuction with a pulse diagram to explain the method according to the invention, Figure 2 shows a pulse diagram for a key-in pulse blanking in connection with the method according to the invention, and Figure 3 shows diagrammatically a solution with regard to equipment for the pulse production for the method according to the invention.

In Figure 1 ,the phase modulation in a video recording and reproduction system with reversible cassette (in which there is a magnetic tape) and automatic track follow-up of the video heads is illustrated diagrammatically in connection with a pulse diagram. In this case, the upper diagram for the auxiliary function, still picture, shows, for the first video head K1, the phase position corresponding to 0 lines and the position of the vertical sync pulse 8 lines after the head change and for the second video head K2 and the phase position of 1.5 lines, the position of the artificial vertical sync pulse at 8 3/4 lines.

The lower diagram of Figure 1 shows, for the auxiliary function, slow motion, for the two video heads K1 and K2 switched alternately, the phase position corresponding to 0 lines for the video head K 1, one line for the video head K2 and two lines for the video head K 1. The position of the alternating artificial vertical sync pulse is illustrated at 8 lines for the switched-on video head K 1, at (8 + 0.5) lines for the video head K2 which is then switched on and at (8 + 1) lines for the video head K1 which is switched on (again).

As illustrated in Figure 1 therefore, the phase time error resulting through the track displacement of 1.5 lines specific to the system during a still picture and slow motion is compensated again by using an alternating, artificial vertical sync pulse, the alternation corresponding to half the phase jump. If, in the above-mentioned video recording and reproduction system, the position of the vertical sync pulse, at normal tape speed, is 8 lines after the moment of switching over the video heads, then the position of the artificial vertical sync pulse for the auxiliary function still picture is switched over alternately from 8 lines to 8 3/4 lines, specifically to the system, while for the auxiliary function slow motion, the positioning of the artificial vertical sync pulse lies alternately at 8 lines, 8 1/2 lines and 9 lines.

In order to avoid a faulty synchronisation of the television receiver connected to the video recording or reproduction equipment, the composite synchronisation signal of the television signal is blanked by a key-in pulse from the moment of switching over the video heads until the appearance of the alternating artificial vertical synchronisation signal, as illustrated in more detail in the pulse diagram of Figure 2. There, in the first line, beginning at the moment of switching over the video heads distinguished by a broken vertical line, a key-in pulse is illustrated which lasts, in time, up to the beginning of the artificial vertical sync pulse illustrated in the second line in Figure 2. Line 3 of Figure 2 shows the FBAS signal after the keying in of the pulse. The key-in pulse preferably lies in the "black region" (black key-in pulse).

Accordingly to the diagrammatic illustration of Figure 3, the alternating artificial vertical sync pulses are produced in a unit 1 and supplied to the Y assembly 2 (luminance-signal processing circuit) of the video recording or reproduction equipment.

The Y assembly 2 also receives from the unit 1 the key-in pulses explained in more detail above as well as pulses for switching over the video head. A drop-out recognition is intended to symbolize a connection from the Y assembly 2 to the unit 1 which renders possible an automatic recognition.

At normal speed of the video recording or reproduction equipment, the artificial vertical sync pulse may be used never, permanently or only in the absence of the original vertical sync pulse.

Accordingly, the absence if notified by a drop-out circuit of the pulse-producing unit 1.

According to Figure 3, status signals for still picture, reproduction, slow motion etc, are supplied to the unit 1 as input signals for the selection of the alternation and the vertical sync pulses from the transmitter. The vertical sync pulses from the transmitter and the production of the artificial vertical sync pulses at the unit 1 drop out, for example, during the recording function of the video recording and/or reproduction equipment.

A sequential network or a microcomputer may be provided as the unit 1 for the production of the alternating artificial vertical sync pulse.

In the case of a time-lapse operation provided in the video recording and/or reproduction equipment, a vertical displacement of the television picture occurs as a result of the follow up of the video head wheel speed. This effect is also compensated again by the artificial vertical sync pulse, in that the time lag between the moment of switching over the video heads and the artificial vertical sync pulse is adjusted.

Accordingly, a microcomputer provided for the production of the alternating artificial sync pulse can also be used at the same time for producing the key-in pulse, producing the video-head switching pulse, the drop-out recognition and the time-lapse operation just outlined.

Claims

1. A method of or apparatus for compensating the phase modulation of the vertical sync pulse for the auxiliary functions of still picture and slowmotion in video recording and/or reproduction equipment, wherein an appropriate artificial vertical sync pulse is used which compensates the phase modulation.

2. A method or apparatus as claimed in Claim 1, wherein the displacement of the artificial vertical sync pulse, relative to the moment of switching of the head, in relation to the vertical sync pulse received from the recording medium corresponds to half the amplitude of the phase modulation.

3. A method or apparatus as claimed in Claim 1, wherein the composite synchronisation signal is blanked by a key-in pulse before the vertical sync pulse in time.

4. A method or apparatus as claimed in Claim 3, wherein the key-in pulse preferably lies in the "black region".

5. A method or apparatus as claimed in claim 1, 2, 3 or 4 for use in a video recording and/or reproduction system wherein the position of the vertical sync pulse lies, at normal tape speed, a specific number of lines after the switching over of the video heads and there is a track displacement corresponding to a multiple -- possibly not integral - of lines, wherein for the still-picture function and the slow-motion function, the position in time of the artificial vertical sync pulse is switched over alternatively in relation to the moment of switching the head.

6. A method or apparatus as claimed in Claim 5 for use in a video recording and/or reproduction system wherein the position of the vertical sync pulse lies, at normal tape speed, eight lines after the switching over of the video heads and there is a track displacement of 1.5 lines, wherein for the still-picture function, the position of the artificial vertical sync pulse is switched over alternately from 8 lines to 8 3/4 lines in relation to the moment of switching the head.

7. A method or apparatus as claimed in Claim 5 for use in a video recording and/or reproduction system wherein the position of the vertical sync pulse lies, at normal tape speed, 8 lines after the switching over of the video heads and there is a track displacement of 1.5 lines, wherein for the flow-motion function, the position of the artificial vertical sync pulse is switched over alternatively to 8 lines, 8 1/2 lines and 9 lines.

8. A method or apparatus as claimed in one of the preceding Claims 1 to 7, wherein a microcomputer is provided to produce the alternating artificial vertical sync pulse.

9. A method or apparatus as claimed in Claim 8 appended to claim 3 or 4, wherein the microcomputer is also provided for producing the key-in pulse as well as producing the video-head switching pulse, a time-lapse operation and a drop-out scanning, status signals for still picture, reproduction, slow-motion etc. being supplied to the microcomputer as input signals for the selection of the alternating.

10. A method or apparatus as claimed in one of the preceding Claims 1 to 7, wherein a sequential network is provided to produce the alternating artificial vertical sync pulse.

11. A method as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

12. Apparatus for compensating the phase modulation of the vertical sync pulse for still picture and slow motion functions in a video recording and/or reproduction equipment, said apparatus being substantially as herein described with reference to the accompanying drawings.