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From: thant@horus.sgi.com (Thant Tessman)
Newsgroups: comp.graphics
Subject: Re: Color perception (Was another @#*! VGA article)
Message-ID: <1503@odin.SGI.COM>
Date: 17 Nov 89 16:51:43 GMT
References: <18219@watdragon.waterloo.edu> <824@uwm.edu> <391@ucsvc.ucs.unimelb.edu.au> <3667@celit.fps.com>
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Reply-To: thant@horus.sgi.com (Thant Tessman)
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In article <18219@watdragon.waterloo.edu>, rsingh1@dahlia.waterloo.edu writes:
> So.. What was this all started by?  64 shades of grey enough?
> 
> Ok.  First, people talk about bits and things, but you have to understand
> that the human body is analog, and organic.  Which means that in some
> situations, it is more responsive to certain things than at others.
> 

Actually, the human brain isn't really analog or digital in the sense
that humans like to think when they build machines.  Inputs into
a neuron are 'digitized'  in the sense that the neuron either fires or
it doesn't.  (This seems to be a very important trick for maintaining
signal quality.)  The information transmitted is contained in the 
rate at which cells fire.  In this sense the brain is (sort of) analog.

I don't know if someone has come out and stated it outright yet,
but the eye is not only not very good at telling the difference between
absolute brightness levels, but it doesn't even seem like it tries to be.

What the eye does very well is judge relative changes in brightness
(and colors) and turn that information into edges and surfaces.  This
makes sense because the important information to gather from
the environment is information independent of the lighting conditions.

So if one block at a certain brightness is shown next to *but not touching*
another block at a different brightness, the eye will be much less sensitive
to the difference in brightnesses.  If, however, they are touching, it is
easy to see very small differences in brightness as a line running
between them.

I'm pretty sure (although  I have no proof) that the people who make 
claims like "64 shades of grey are enough" are doing the first kind
of test, not the second.

It is possible to tell a difference between an image using 36 bits
of color and the same image using 24 bits of color, let alone the
difference between a 6 bit and an 8 bit monochrome image.

thant

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There are 336 dimples on the standard golf ball.