cranmer@trwrba.UUCP (Daniel N. Cranmer) (10/26/84)
Hello, Does any one know of a set up that allows one to use a video cassette recorder to record graphics directly from the computer. One of the problems we have noted is that our high resolution graphics monitors are too high-res for normal TV. Also the problem of recording via a camera leaves a lot to be desired. Any help would be appreciated. (Thanks!) TRW Dan Cranmer One Space Park 92/3385 Redondo Beach, CA 90278 (213)535-4509
herbie@watdcsu.UUCP (Herb Chong, Computing Services) (10/28/84)
As far I as know, using a VTR/VCR designed for the NTSC broadcast system
will not record to high enough resolution to use even on an IBM PC screen
at high res. It limits you to about 300 by 200 pixel resolution unless
you have an exceptional VTR/VCR. Most people that I have heard of doing this
use special recorders. I don't know whether these are custom built or modified.The bandwith of signal of a VTR/VCR isn't high enough unless you do things like
increase the speed of tape and/or the head rotation.
Herb...
I'm user-friendly -- I don't byte, I nybble....
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BITNET: herbie at watdcs,herbie at watdcsudmmartindale@watcgl.UUCP (Dave Martindale) (10/29/84)
There are at least three different issues involved when trying to record computer graphics output on VTR's. The first is matching the format of the frame buffer to the NTSC video standard, in terms of the number of pixels displayed. NTSC provides 484 full lines of video, interlaced. You thus need a frame buffer that displays about that many lines. 1024x1024 displays just cannot be encoded directly into NTSC format. Also, the frame buffer has to be able to put out the data in an interlaced format: all the even lines in one field, all the odd ones in the next field. The number of pixels horizontally doesn't matter as much, as long as the horizontal sweep rate is about 15.73KHz. However, the resolution that will actually be visible on the screen in the horizontal direction will be between 300-400 pixels in luminance (brightness) with somewhat less colour resolution. So displaying a vertical line that is only one pixel wide will not look very good if it is a different colour from the background. These are fundamental (bandwidth) limitations of the NTSC standard and cannot be bypassed if you are using standard video equipment. The next problem is synchronization. NTSC specifies a horizontal sweep of 15734 Hz, a vertical sweep of 59.94Hz, a particular number of lines of vertical blanking, and a particular structure of the pulses during the vertical interval. Some frame buffers don't put out video that looks anything like this standard at all; 1000-line systems usually use a 32KHz horizontal sweep, for example. Some frame buffers that are designed to be displayed on standard TV have the rates "about right" and may be good enough for the TV to lock onto, but not good enough for a VTR to handle. Only a few frame buffers provide real, RS170 (NTSC) sync in their video signals. Another way of getting good sync is to use a standard TV sync generator, and lock your frame buffer to it; again only a few frame buffers seem to provide external sync capability. The last problem is encoded signal quality. The TV encoders that generate RF for feeding to a TV set seem to be pretty awful. Even the cheap (all-in-one) RGB-to-NTSC encoders are not very good. But if you get a broadcast quality NTSC encoder (intended for encoding the output of a studio colour camera) and your frame buffer puts out RGB signals compatible with this encoder, you can get quite good results (subject to the bandwidth limitations mentioned above). In the computer graphics lab at Waterloo, we have a Leitch sync generator and a Cox NTSC encoder (both intended for TV studio use). The frame buffer in use is an Adage/Ikonas RDS3000, which handles external sync plus has enough flexibility in its video timing to fit either a 512x484 or 640x484 into the video frame. We record on an ordinary Sony U-Matic 3/4 inch recorder, though the video produced is standard so any sort of NTSC VTR would work. The quality is surprisingly good. However, for this quality of equipment, you'll have to spend $5K+, and it takes an oscilloscope to set it up properly. And, of course, the Ikonas is not included in that price. Generating good-quality video is not cheap, at the moment. If you have a graphics system of some sort that cannot be coerced into producing NTSC timing of its signal at all, then there are "black boxes" that can convert video from a variety of formats to NTSC video. They are basically frame buffers in their own right, which digitize the incoming signal and store it in memory using the timing of the incoming signal, simultaneous with the contents of memory being scanned and turned back into video at NTSC rates. Cox makes one; other manufacturers must do so as well. They are all likely to cost $10K+. To understand better what is going on in the process of generating video signals, try borrowing a book on television engineering from your nearby university library. Dave Martindale Computer Graphics Lab University of Waterloo
keithd@cadovax.UUCP (Keith Doyle) (10/31/84)
A cheaper, but perhaps not as effective method would be to go to film
first and then convert back to video. Unfortunately it may be necessary
to single frame the film in order to avoid obnoxious sync bars on the film.
If the computer can control the shutter of the camera, and can 'single shot'
or accurately control the video output so that each camera exposure contains
a consistant number of vertical sweeps of the picture, the entire process
can then be automated via program control. It's concievable that this
could be done with very low budget equipment, (super 8 etc..) if price
is important, and the resultant film can then be transferred to whatever
format video you like by local film or video labs.
However, I have no idea what effect this will have on the resultant resolution
of the final video tape. Turn around time is also very long, but you get
what you can pay for.
Keith Doyle
{ucbvax,decvax}!trwrb!cadovax!keithddmmartindale@watcgl.UUCP (Dave Martindale) (11/02/84)
Re using colour film as a way of getting good video: There definitely is equipment around that will do high-quality transfer from film to video. The equipment itself is very expensive, but you should be able to pay someone to do the transfer. However, getting good images on film isn't easy. Just photographing the face of the monitor doesn't work too well - the colours seem to desaturate a lot (we tried doing some animation tests using exactly this technique). There are devices around that are designed specifically for producing good-quality photographic images; typically they use a black&white CRT and colour filters to generate colour images. One real advantage of such equipment over video equipment that generates NTSC directly is that your frame buffer doesn't need to accept an external sync signal. Anything that the camera's monitor will lock to is fine. On the other hand, to produce good, stable animation on film, you need a film transport for your camera which holds a fair length of film and uses pin registration of the film for precise positioning from one frame to the next. Such a camera might cost you almost as much as the video equipment I mentioned, but in cases where you can use the final output on film, the quality can be much better than standard television can ever provide even on the best possible equipment. A difference between this approach and generating video directly is that the direct-to-video approach allows you to record in real time and only in real time (unless you have a VTR which can record single frames, still a very expensive item - $75000), while a film cameras allows you to record only in non-real time. So the video approach allows you to record interaction as it happens, while film is much better for recording animation.