Path: utzoo!attcan!utgpu!watmath!watdragon!dahlia!rsingh1
From: rsingh1@dahlia.waterloo.edu
Newsgroups: comp.graphics
Subject: Re: Color perception (Was another @#*! VGA article)
Summary: Colour perception junk (my thoughts)
Message-ID: <18219@watdragon.waterloo.edu>
Date: 16 Nov 89 03:34:57 GMT
References: <824@uwm.edu> <391@ucsvc.ucs.unimelb.edu.au> <3667@celit.fps.com>
Sender: daemon@watdragon.waterloo.edu
Reply-To: rsingh1@dahlia.waterloo.edu ()
Organization: U. of Waterloo, Ontario
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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.

This makes it dificult to define limits of sombodies ability to do
something or other.  But a way to tackle the colour question would be
to use an analogy like this:

Weight ratio detection stuff.  That is, if you have to weights, one in
each hand, and they were both equal.  Your brain might fool you into
thinking one is heavier, or you might just say you can't really tell.
Subsequently, if you increase the weight by one gram, and the initial
weight was about 1kg, would you notice?  Doubtful.  But once one weight
is x% heavier than the other, you notice.
 
Likewise, if one colour is x% brighter than the other, you notice.
 
Just like the stars in the sky at daytime.  While they are still there,
as well as the ambient lighting present at night, you can't see them.
Our visual sensibilities have been thrown out of balance.
 
Also you have to take into account that the eye has the rods, cones and
other junk, with each component reacting to different stimuli.  You also
should know that the monitor doesn't re-produce the entire spectrum.  It
lacks in quite a few extremes, most notably in the greens with a bit in the
violet and crimson.  Compound this with the different sensetivity ranges
of different intensities of the colour and you can see that it all gets
very very complicated.
 
In simple grey-scale, it's good to have plenty (256 shades, for me, is a 
decent working number) of greys available.  Why?  Well, because for images,
you want a good range for the overall ambiance of the image.  EX. If the
image was a photograph, well ballanced, with a high-spread of greys ranging
from bright to quite dark, then fewer greys could actualy do.  But if the
image is basicaly dark, then it would never use the brighter greys, so your
palette of 64 greys now becomes a palette of around 10 greys.  Here, the eye
picks up lots of stair-casing.
 
The effect is worse with colour displays.  Consider graphics by an amiga,
compared with a VGA.  That's just the difference between 4 and 6 bit.
(4096 and 262144 colours (or shades/tint's/tones/whatevermakesyouhappy),
But pictures done on the VGA, even at the lower resolutions appear MUCH
less grainy.  Because the shadows and dark regions have more degrees that
they can fade through than the amiga (dozens more).  Where on the amiga,
a shadow would be 2 shades (an obvious staircase), vga has a smoother one.
 
It's just the simple fact that most people can tell the difference.  A
trained eye (like mine :-) can tell the # of pixels or resolution of
scann's and things about as well as a printer can tell what one kind of
offset type from another, one version of a font from another.  And while
most of us won't pick up on it consiously, we do 'see it'.  And as time
goes on, and you happen to be walking by a display where Itarbm computers
are sold, you'll notice if the Itarbm computer is using only 16 bit
graphics, and your workstation has 32.  Just wait and see!

--------------------------
Paul Sop - Prez #2 of Spaghetti Western Words and Images