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From: rick@hanauma.stanford.edu (Richard Ottolini)
Newsgroups: comp.graphics
Subject: Re: Re: Workstations that can record/play realtime video
Message-ID: <6640@portia.Stanford.EDU>
Date: 14 Nov 89 17:01:18 GMT
References: <6509@portia.Stanford.EDU> <1360003@hpspcoi.HP.COM>
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Reply-To: rick@hanauma.UUCP (Richard Ottolini)
Organization: Stanford University, Dept. of Geophysics
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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.

NTSC is rated at 3.5 MHz or 32 GB / hour given 2bits per Hertz, the
minimum encoding under Nyquist limit.  Most VHS systems barely reach 1 MHz.
NTSC cheats by smearing the spatial intensity resolution a little and color
resolution alot, but it fools the human visual system.  Uncompressed digital 
is 100 GB, but I mention 95% compression schemes are not difficult (SIGGRAPH
talk, Sun TAAC board), reducing the need to about 5 GB / hour.
New mass storage systems such as Exabyte fit 2 GB digital on a standard videotape
and I believe it it is almost 4 GB if one includes all the extra error checking.