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From: madler@piglet.caltech.edu (Mark Adler)
Newsgroups: comp.graphics,comp.sys.next
Subject: Re: Next machine as animation platform
Keywords: NeXTdimension, JPEG
Message-ID: <1990Nov17.234727.10513@nntp-server.caltech.edu>
Date: 17 Nov 90 23:47:27 GMT
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Dermot Tynan (dtynan@zorba.Tynan.COM) notices:
>> Actually, referring to the American Cinematographers Manual (which I
>> *don't* have in front of me, so forgive any roundoff (?) errors), not
>> only is the definition for "broadcast quality" defined as 720x484, it
>> also requires "from 8 to 12 bits" per color!  Seeing as they only used
>> approximately 5 bits per color, they probably figured they had
>> compromised anyway, and might as well use 640x480, which seems to be
>> deep-rooted in ancient mysticism, along with 80-characters per line,
>> and 24 lines per screen (monitor bandwidth and P31 resolution black-
>> magic incantations heard in the background).

Well, sort of.  Computing 5.3 bits per color is misleading.  There are
still 8 bits each for Y, U, and V---it's just that there are half as
many U's and V's.  I said there was an average of 16 bits per pixel,
but really there are 32 bits per two pixels.  The YUV gets converted
to RGB in a way that gives a full eight bits of resolution to R, G, and
B for each pixel, except that there is a subtle correlation between
adjacent even and odd pixels.

As someone else pointed out, U and V combined get the same bandwidth that
Y does on an NTSC broadcast, which is how this elementary compression
of RGB by 3:2 retains broadcast quality.  However, one might consider
"broadcast quality" to be an oxymoron.

The numbers 480 and 640 do seem to have Kabbalistic origins, along with
24 and 80.

Mark Adler
madler@piglet.caltech.edu