From: lowen@lorc.UUCP (Lamar Owen)
Newsgroups: alt.folklore.computers,rec.games.int-fiction
Subject: Re: Screen colors (Was Re: Zork/Dungeon)
Date: Fri, 09 Oct 92 12:46:11 EDT
Organization: LORC Enterprises

xeno@iastate.edu (Gary L Snethen) writes:
> In <Xs76RB1w164w@lorc.UUCP> lowen@lorc.UUCP (Lamar Owen) writes:
> >xeno@iastate.edu (Gary L Snethen) writes:
> >> That would be 4096 x 4096 resolution...  Pretty snazzy monitor!
> >This is very true.  But, even with a 4096x4096 screen, you still couldn't se
> >16 million colors.  Why?  The eye can only distinguish about 4 milllion colo
> >So, those other 12 million are just useless baggage.  Although using 24 bits
> >for color info is easy on the hardware and the programmer, these days, due t
> >IBM's success at pushing 8-bit bytes.
> 
> Interesting observation...
> 
> However, with 24 bits, you can only represent 256 different values of
> true grey...  and I assure you that my eye can distinguish more than 256
> shades of grey, so therefore either more bits are needed or the bits availabl
> must be used more effectively to cover the entire spectrum that the human
> eye can distinguish.

Also an interesting observation.  The eye, due to its dual nature, is very 
sensitive to intensity variations in the GREY realm.  Why? Due to the splitting
of the retina into cones and rods.  If I am not mistaken, cones perceive hue
mostly, and rods perceive intensity.  Now, for survival, it is important to
be able to distinguish an object even in low light levels.  This either implies
a logarithmic scaling of intensity, or a generally better resolution of
intensity.  Note that, at low light levels, everything is grey.  Very little
color, since the cones don't do as well in low light.

In fact, the eye is more sensitive to some color frequencies than others.  I
do not remember exactly which right at this moment, but the very act of
color combining in a TV set makes use of this property to get the best
possible perceived chroma resolution.  Acckk!  I wish I could remember my
chroma bandpass filter gain ratios!  (NTSC, of course.  PAL uses a different
ratio set because of the different modulation technique).

Note also that the eye doesn't really use a primary color model for sight. As
far as the eye is concerned, there is only a frequency continuum, not three
primaries.  Although, if you look at a color spectrum, the three traditional
primaries are by far the most noticeable colors.  How then does the combination
of RGB produce such a wide range of color?  Well, in this case a process which
is normally not ever desired produces a desireable effect: Intermodulation
distortion allows RGB devices (or CYMK) to emulate a real color picture.  You
combine the three primary frequencies in various ratios, and you end up with 
some very complex intermod products.  However, an intermod white isn't quite as
WHITE as a _real_ white, which would be an even frquency distribution from red
to blue  in real light.  However, the phosphors in most CRT's are wideband 
enough to cause the intermod to nearly spread across the whole spectrum.

So, to really produce real color, you would need more than just RGB.  The CYMK
system is closer--with 65535 shades of grey available.  In fact, CYMK can be
fit into 24 bits by noting which color the eye is the most sensitive to.

Now, the possible combinations of CYMK would, to an extent overlap.  In fact,
there are lots of overlap.  By reducing the matrix to the eye's real color
range, a true color system could be built that would match the eye's response
exactly.  Basically, your pixel bit values would point to the proper color in
the palette of the eye's possible colors.  Now, all we need is a largish ROM
and a 32-bit RAMDAC to get what we want out of 4 million colors.  This
4 million color figure was quoted from a doctor.


> ---Xeno

--

Lamar Owen, Systems Consultant, GE Lighting Systems, Hendersonville, NC
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 Opinions expressed herein are the author's and do not reflect policy
   or opinions of the General Electric Company or its subsidiaries.
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Newsgroups: alt.folklore.computers,comp.unix.admin