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From: dave@imax.uucp (Dave Martindale)
Newsgroups: comp.graphics
Subject: Re: Re: Workstations that can record/play realtime video
Message-ID: <1989Nov15.192426.11410@imax.uucp>
Date: 15 Nov 89 19:24:26 GMT
References: <6509@portia.Stanford.EDU> <1360003@hpspcoi.HP.COM>
Reply-To: dave@imax.UUCP (Dave Martindale)
Organization: Imax Systems Corporation, Oakville Ontario
Lines: 29

In article <1360003@hpspcoi.HP.COM> jchristy@hpspcoi.HP.COM (Jim Christy) writes:
>
>> VHS quality 24 bits x 640 pixels x 480 lines x 30 Hertz x 3600 seconds
>> is 100 gigabytes uncompressed.
>
>This would imply that a standard VHS cassette tape has nearly 200 GB of 
>storage capacity.  Your multiplication is OK, but I think that's a little
>high, else we would all be using these as mass storage backup devices.
>Granted, this signal is stored in analog not digital form in the typical
>recorder.  

That computation is really saying that you need 100 Gb to store 1 hour
of video at *better than broadcast quality*.  Your image source needs
to be better than the recording medium.  Even if you used the very
best analog video recorder, you wouldn't expect to get 100 Gb back
from it.

And that figure assumes you store the image as RGB.  If you separate
luminance from chrominance, you can get away with less spatial
resolution in the two colour channels (and probably less intensity
resolution too) while maintaining broadcast quality.

Of course, VHS has poorer S/N and less resolution that broadcast
quality, so fewer bits would be needed for "VHS quality",
(if you can stand to watch VHS quality!).

To come from the other end, there is a digital data recorder that
stores 5 Gb on a VHS cassette, so its storage capacity is definitely
above that.