GB2229889A

GB2229889A - Videodisc and videodisc player, and vision mixing simulator using the same

Info

Publication number: GB2229889A
Application number: GB9004597A
Authority: GB
Inventors: Andrew Brandon Finney; Francis John David Allen
Original assignee: British Broadcasting Corp
Current assignee: British Broadcasting Corp
Priority date: 1989-03-03
Filing date: 1990-03-01
Publication date: 1990-10-03
Anticipated expiration: 2010-03-01
Also published as: GB9004597D0; GB2260463A; GB2229889B; GB8904906D0; GB9224798D0; GB2260463B

Abstract

An interactive video mixing simulator system uses a videodisc on which the outputs of a plurality of television cameras are recorded in interleaved format. There are three sequences of frames with blocks of 20 frames of each sequence being cyclically interleaved. On replay of one sequence, the read head reads one block and then jumps two blocks (40 frames). To change sequences, the size of the jump is altered for one jump only. By the interleaving of blocks the time interval between discontinuities in the accompanying audio signal is increased from 40ms to 0.8s making them much easier to mask. The blocks may include an extra frame such that the first frame of each block repeats the last frame of the preceding block in the same sequence, thus reducing the visible discontinuities on the jump. <IMAGE>

Description

VIDEODISC AND VIDEODISC PLAYER, AND VISION MIXING SIMULATOR USING THE This invention relates to the storage and replay of changing visual images using a videodisc, that is to say a so-called "laser disc, or a compact disc (CD), or the like, capable of storing visual images in such a way that selected frames of the images can be made available as desired relatively rapidly.

In such a videodisc it has been proposed to record several different sequences of images with the frames of the sequences interleaved. Thus if n video image sequences are interleaved on a frame by frame basis, when reading the disc the videodisc player selects just one in every n frames, so as to present sequentially the frames of just one sequence. The player skips the intervening n - 1 frames. This has the advantage that it is very easy to change from one sequence to another. This is achieved by the player skipping less than n - 1 frames on one occasion only. This then locates it on a frame from a different sequence. After that it continues to skip n - 1 frames until another change of sequence is required.

There are limits on the actual capability of the read head of the player to jump during the conventional frame blanking period of a video signal of broadcasting standard. For example, the Philips 400 series laser disc players can jump plus or minus 50 two-field frames within this period. The jump is in fact achieved by flipping a mirror, and after the jump the main laser carriage has to "relax" or return to its centre position before another 50 frame jump can take place. Practical considerations in fact limit the on-the-fly instant jumps to 20 frames, because of this relaxing of the laser carriage.

Each sequence of frames may conveniently be termed a "universe", and thus the inaxinturn number of universes that can be interleaved on a frame-by-frame basis is about 20, with the player playing one frame and then skipping 19.

we have appreciated that although pictures are relatively easy to handle to produce interleaved sequences, by videotape (VT) editing or by optical film printing, the sound is a far greater problem if this is recorded along with the images. Because the videodisc player gets its sound from exactly the same carrier signal as the pictures, the sound will be played with discontinuities whenever the laser head jumps frames. With the interleave described above these discontinuities occur once per frame period, which, for a 50 field per second picture, is 40ms, and this adds a high level of pulse noise to the sound which it is difficult to remove or mask.

The pulse rate frequency itself is 25Hz, or 30Hz for a U.S. standard player. Also the 40 ms segments are too short for the VT edit to handle; separate sophisticated digital editing techniques would be needed.

In accordance with this invention in a first aspect we propose that the interleaving of frames comprises the interleaving of n blocks of i frames, where j is a number sufficiently greater than one such as to reduce the noise pulse rate in the audio channel to a point where it can adequately be disguised.

The blocks of frames may contain at least four frames in each block. Preferably j will be at least ten, and typically is around 20.

The use of a block size of the order of 20 frames has distinct advantages. On recording of the disc, it is not difficult for the relevant audio to be edited with the video, since 20 frame segments are large enough for a videotape editing facility to edit sound with pictures.

On playback a click every four-fifths of a second is less of a problem than 25 clicks a second. It should be possible to use a device such as those used to "de-click" graophone records to disguise these with little degradation of the final sound.

Interleaving blocks also has the effect of reducing the apparent errors if the videodisc player "mis-jumps".

The invention also provides a videodisc having recorded thereon a plurality of sequences of frames with the sequences being interleaved, the interleaving comprising the interleaving of blocks each of a plurality of frames from each sequence.

In accordance with a further aspect of the invention we provide an interactive video mixing simulator system comprising a videodisc having recorded thereon a plurality of video signals, such as the output of a plurality of television cameras, in a plurality of sequences in interleaved format, a videodisc player for replaying the recorded images such that one of the interleaved sequences is replayed at a time, and manually operable means for changing the selected sequence being replayed, such as to simulate a cut from one camera to another.

One example of the use of such a system will now be briefly described with reference to the drawings, in which: Figure 1 is a diagram illustrating the sequence of frames on a videodisc and the manner in which the jumps are made; and Figure 2 is a detail illustrating a modification of the system in which certain frames are duplicated.

The example to be described is concerned with the simulation of a television control gallery which allows interactive training of directors, production assistants, vision mixers, and others. The system uses a Philips 400 series 12 inch videodisc player. The disc holds pictures from three cameras together with a sound channel and allows trainees to cut between the camera outputs to produce an edited result.

The outputs of the three cameras are recorded in cyclically interleaved fashion with blocks of 20 frames from each camera being interleaved. Normally the camera outputs will be recorded on tape and the tapes edited to produce a recording with the interleaved blocks of frames. The interleaving is produced on a final tape which becomes the master from which the videodisc is pressed. When the trainee is steadily using the output of one camera, the player skips 40 frames at the end of each block so as to pick up again at the start of the next block from the same camera.

If the trainee indicates that a change of camera is required, the player instead may make a once-only jump of 20 frames or omit the jump altogether, depending on which of the other cameras is now required to be fed to the output. More generally, a jump of plus or minus 20 or plus or minus 40 may be used. It will be appreciated that the cut may be initiated at any point in the replay of a block, in which case a different number of frames may be jumped so as to pick up at the start of the next block from another camera, or at the corresponding point in the next block.

Figure 1 illustrates such a system. In this illustrative system only ten frames are shown as constituting each block so as to show the frames mDre clearly. The frames are shown at the top of the figure in their arrangement on the videodisc track. At (a) is illustrated the sequence of jumps when the output of camera 1 is being displayed continuously. The head reads the j (ten) frames from camera 1 and then jumps (n-l)j frames, i.e. twenty frames, so as to pick up at the start of the next block of frames fram camera 1.

At (b) and (c) are illustrated the sequences of jumps at the point where the output of camera 1 is changed to select the output of camera 3 or camera 2 respectively. In (b) there is one jump of ten frames instead of the usual twenty, and at (c) the jump reduces to a jump of zero frames, i.e. no jump at all.

The recorded frames in fact are each split. The greater part of the frame area comprises the output of the designated camera, but a small part of the frame, in fact the bottom of the frame, is used to show the outputs of all three cameras including the two "non-selected" cameras. In this way a single CRT display can be used to display the outputs of all three cameras to the trainee.

This also means that the bottom portion of each displayed frame is the same. This helps to make the jump less visible, for the following reason. In fact there remains a small problem caused by the exact timing of the jump that takes place. Although in theory the jump should all take place within field blanking, in practice it is carried out a little before the field blanking so that the read head will be able to read a 24 bit code in the next blanking period.

This read is needed to confirm that the jump has been successful.

Therefore the read head leaves the "departure" field before it has completely finished and lands before the intended "arrival" field has started. This shows as a small portion of the field before the intended arrival field, visible mamentarily at the bottom of the frame. If the bottom part of the frame of each of the sequences (universes) is the same, this will be barely noticeable.

An alternative way of overcoming this problem is to record an additional frame at the start of each block, this frame being the same as the last frame of the previous block from that universe.

This means that each block is now one frame longer than previously, so a 20 frame block now becomes a 21 frame block. The read head then jumps from near the end of the last frame of one block to the corresponding point near the end of the first frame of the next block of the same universe, as illustrated in Figure 2. The actual "landing" field will thus be identical to the "take-off" field and so will minimi6e visible discontinuity. Figure 2 shows part of the sequence of frames from cameras 1, 2 and 3. Any remaining portion of the actual landing field that is displayed is from the correct camera and not from camera 3 instead, as would happen if the duplicate field were not present. As it is impractical to duplicate a single field the whole of the relevant frame (both fields) is duplicated instead.This has the added benefit of removing discontinuities caused by premature jumping from the first field of the take-of f frame. The continuous play algorithm can now be written as play j frames; jump [ (n-l)j+n) frames.

Appropriate software to control the videodisc player can readily be written by those skilled in the art. The user uses a keyboard to interrupt a control loop so as to intercut between universes.

Instead of feeding the output to videotape, the system can simply keep a record of the cuts made by the trainee. In a replay mode the trainee's outputs can then be reproduced exactly for training purposes.

It may be possible to incorporate digital special effects to provide a zoom effect for example, or the use of additional still frames. Other supporting material may be recorded such as captions, photographs, floor plans, the control gallery talk-back, scripts, and so on. Using advanced image processing techniques it may be possible to allow the trainee to re-position cameras on the floorplan, with the system simulating the view of the set from that camera position. Camera moves may similarly be simulated.

The system can, of course, be adapted for the simulation of other real-time systems than that described.

Claims

ClAIMS

1. A videodisc having recorded thereon a plurality of sequences of frames with the sequences being interleaved, the interleaving comprising the interleaving of blocks each of a plurality of frames from each sequence.

2. A videodisc according to claim 1, in which each block comprises at least four frames.

3. A videodisc according to claim 1, in which each block comprises at least ten frames.

4. A videodisc according to claim 1, in which each block comprises not more than 50 frames.

5. A videodisc according to any preceding claim, in which there are at least three interleaved sequences.

6. A videodisc according to any preceding claim in which the bottom portion of the images of each of the sequences is the same.

7. A videodisc according to any preceding claim, in which the first frame or field of each block repeats the last frame or field of the preceding block in the same sequence.

8. An interactive video mixing simulator system comprising a videodisc having recorded thereon a plurality of video signals in a plurality of sequences in interleaved format, a videodisc player for replaying the recorded images such that one of the interleaved sequences is replayed at a time, and manually operable means for changing the selected sequence being replayed, such as to simulate a cut from one camera to another.

9. A system according to claim 8, in which the videodisc has recorded thereon the outputs of a plurality of television cameras.

10. A system according to claim 8 or 9, in which the interleaved format comprises the interleaving of blocks each of a plurality of frames from each sequence.

11. A system according to claim 10, in which the first frame or field of each block repeats the last frame or field of the preceding block in the same sequence.

12. A system according to any of claims 8 to 11, in which in normal operation the player reads the frames from one sequence only and jumps over the intervening sequences, and including means, responsive to the manually-operable means for changing the selected sequence, which means changes the jump size for one jump so as to read a different one of the sequences.

13. A method of storing a plurality of sequences of changing visual images on a videodisc, comprising storing successive frames of the sequences in interleaved format, the interleaving comprising the interleaving of blocks each of a plurality of frames from each sequence, the number of frames in each block being sufficient to reduce the noise pulse rate in the audio channel on replay of the disc.

14. A method according to claim 13, in which each block comprises at least four frames.

15. A method according to claim 13, in which each block comprises at least ten frames.

16. A method according to claim 13, in which each block comprises not more than 50 frames.

17. A method according to any of claims 13 to 16, in which there are at least three interleaved sequences.

18. A method according to any of claims 13 to 17, in which the

19. A method according to any of claims 13 to 18, in which the first frame or field of each block repeats the last frame or field of the preceding block in the same sequence.

20. A method according to any of claims 13 to 19, in which the sequences comprise the outputs of a plurality of respective television cameras.

21. A method of selectively replaying a plurality of sequences of changing visual images recorded on a videodisc, successive frames of the sequences being recorded in interleaved format with the interleaving comprising the interleaving of blocks each comprising a plurality of frames from each sequence, the method comprising in normal operation reading the frames from one sequence only and jumping over the intervening sequences, and when a change of sequence is required altering the jump size for one jump so as to read a different one of the sequences.

22. A method according to claim 21, in which each block comprises at least four frames.

23. A method according to claim 21, in which each block comprises at least ten frames.

24. A method according to claim 2i, in which each block comprises not more than 50 frames.

25. A method according to any of claims 21 to 24, in which there are at least three interleaved sequences.

26. A method according to any of claims 21 to 25, in which the bottom portion of the images of each of the sequences is the same.

27. A method according to any of claims 21 to 26, in which the first frame or field of each block repeats the last frame or field of the preceding block in the same sequence.

28. A videodisc substantially as herein described with reference to the drawings.

29. An interactive video mixing simulator system substantially as herein described with reference to the drawings.

30. A method of storing visual images substantially as herein described with reference to the drawings.

31. A method of selectively replaying visual images substantially as herein described with reference to the drawings.