Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!mit-eddie!uw-beaver!cornell!johnhlee
From: johnhlee@bass.cs.cornell.edu (John H. Lee)
Newsgroups: comp.sys.amiga
Subject: Re: 24/32 Bit Color
Message-ID: <47229@cornell.UUCP>
Date: 17 Oct 90 21:26:49 GMT
References: <33786@nigel.ee.udel.edu>
Sender: nobody@cornell.UUCP
Reply-To: johnhlee@cs.cornell.edu (John H. Lee)
Organization: Cornell Univ. CS Dept, Ithaca NY
Lines: 40
Summary:
Followup-To:

In article <33786@nigel.ee.udel.edu> byrne@muppet.dnet.ge.com writes:
>
>I think I need some education.  I was under the (false?) assumption that the
>human eye could not distinguish 16 million colors (24 bit).  I assumed 24 bits
>was decided as number because it was an even multiple of a byte given the 3
>color components (RGB).  Since most displays don't have 16 million pixels, this
>gives you a great big palette.  But why 32 bit?  Is 32 bit color used because
>it is the word size of most of the popular high performance microprocessors
>(i.e 68020+)?  I don't see it buying you anything from a color stand point
>because who could distinguish adjacent colors from either 24 or 32 bit
>palettes?  Does it help in shading or is it just for data movement speed?
>Seems like overkill.  Thanks,
>
>                        -FB

True, the human eye cannot distinguish 16 million colors individually, but
it can distinquish the difference in shades when placed right next to each
other even when 24 bits are used (8 bits per RGB) and the shades differ by
only one bit.  Human vision enhances contrast at edges, causing a phenomenon
called Mach Bands (I think that's how its spelled) where the lighter side
of an edge seems brighter and the darker side darker.  When the patches of
color are viewed separately, you couldn't tell the difference.

This is especially a problem when trying to do shading, like for the sky
from a dark horizon to a brighter zenith when even with 24 bit resolution
people can see bands of different shades.  32 bit resolution would help
eliminate this.  Why 32 bits?  Because it's a nice multiple of 8 bit bytes
and most processors these days (not just the 680x0 family) handle 32 bit
longwords as a natural data type.  Too bad it's not a nice multiple of 3.

Of course, 32 bit graphics vs. 24 bits won't matter the slightist bit to
anyone except mostly computer graphics and image processing people.  I
doubt that most professional video production people will ever need it.
It makes no difference to 95% of the common PC users out there, despite
what Marc Bennett says.  :-)

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The DiskDoctor threatens the crew!  Next time on AmigaDos: The Next Generation.
	John Lee		Internet: johnhlee@cs.cornell.edu
The above opinions of those of the user, and not of this machine.