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From: lilley@v5.cgu.mcc.ac.uk (Chris Lilley)
Subject: Re: 48-bit graphics...
Message-ID: <1993Apr27.151405.11576@nessie.mcc.ac.uk>
Keywords: 48-bit alpha channel IMAGE
Lines: 41
Sender: lilley@umrcc.cgu.mcc.ac.uk (Chris Lilley)
Reply-To: C.C.Lilley@mcc.ac.uk
Organization: Computer Graphics Unit, MCC
References:  <1993Apr24.201117.26232@cs.wisc.edu>
Date: Tue, 27 Apr 1993 15:14:05 GMT


In article <1993Apr24.201117.26232@cs.wisc.edu>, oehler@yar.cs.wisc.edu (Wonko
the Sane) writes:

>	I was recently talking to a possible employer ( mine! :-) ) and he made a
>reference to a 48-bit graphics computer/image processing system.  I seem to
>remember it being called IMAGE or something akin to that.  Anyway, he claimed
>it had 48-bit color + a 12-bit alpha channel.  That's 60 bits of info--what
>could that possibly be for?  Specifically the 48-bit color?  That's 280
>trillion colors, many more than the human eye can resolve.  Is this an
>anti-aliasing thing?  Or is this just some magic number to make it work better
>with a certain processor.

Well 48 bit colour *could* be for improved resolution but 16 bits per channel
seems like a bit excessive. I have seen a paper that quoted 10 bits per channel
of 12 bits for computational precision. More than that would seem to be wasted.

Perhaps the frame buffer uses another colourspace which needs more bits to
represent the full range - RGB is a cube so it is a compact encoding.

Most likely however is that there are two separate 24 bit (8 bits per component)
frame buffers. This set up, called double buffering, allows a complex 3d picture
to be built up on one buffer while the other buffer (containing the previous
frame) is displayed. This makes for smoother animation.

>(sadly, I have access to none of them.  Just a DEC 5000/25.  Sigh.)

Well hey if you want to brag about numbers, the 5000 range can take a PXG Turbo+
card with 96 bits per pixel. Full double buffering (Two 24 bit buffers), a 24
bit Z buffer and an extra 24 bit buffer for off screen image storage.

Mind you the card costs more than your workstation.

--
Chris Lilley
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