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From: matt@karazm.math.uh.edu (Matt Emerson)
Subject: Re: ColorStation questions
Message-ID: <1991Apr25.180420.9712@menudo.uh.edu>
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Organization: University of Houston -- Department of Mathematics
References: <1991Apr24.082948.17763@cs.ucla.edu> <559@rosie.NeXT.COM> <1991Apr24.231003@ece.arizona.edu>
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Date: Thu, 25 Apr 1991 18:04:20 GMT

In article <1991Apr24.231003@ece.arizona.edu> dan@ece.arizona.edu (Dan Filiberti) writes:
>
>Yes, it is, of the 4096 different color values each pixel can take on,
>16 of them are pure gray (Red == Green == Blue). However, PostScript 
>employs dithering to display a lot more colors than can be represented
>
>This is just wonderful! Here, we thought we were getting a good price
>on a workstation, and 4096 simultaneous colors to boot.  Now, we find
>that the price isn't the only thing that is cheap.  Let's look at the
>bigger picture.  NeXT claims that it can "display" 4096 colors on the
>screen at one time.  What they don't tell you, is that you really have
>control over only 16 colors!.  The rest are all permutations of the
>six that you pick!  You know that is just lovely...once again research
>succumbs to the will of the masses.

There are pros and cons to having a static color palette. It seems to me that
there has been a lot of discussion on the bad aspects, but little mention
of the benefits.

Dan points out the cons of this arrangement. In certain applications, it may
be useful to restrict attention to a particular subset of colors. One thing
that comes to mind is greyscale work.

However, I simply cannot agree that having a static palette is "cheap." The
main idea behind NeXT's display philosophy is *device independence*. This is
at the heart of the whole idea of Display PostScript. A static palette can
guarantee an even distribution of colors for the PS interpreter to choose
from -- this results in better color fidelity *in general*.

To elaborate:
  With a color look-up table, you select your palette of colors (say 256) and
draw to your heart's content. But now what happens when you move your program
to hardware that supports more colors? You still only use the same 256 you
selected. And what if you want to run your program on hardware that supports
only 16 colors?  Undoubtedly, it'll have some noticable flaws.
  With static palettes, you just ask for any color you want.  If you have
hardware that supports full color, you obviously get exactly what you asked
for. If you don't, you get the hardware's best approximation, be that a dither
pattern of 4096 colors, 256 colors, 4 greys, whatever. And you, the programmer,
don't have to worry about it one bit. You just say: gimme rgb(123,54,90).

Sun's NeWS server also uses a static palette for these same reasons.

>Our research deals with images of skin, which unfortunately, may contain
>over 256 shades of red, pink, various browns, greys, blues, and who
>knows what else.  We are trying to determine which colors are important,
>and which aren't in the diagnosis of skin disorders.  How can we do
>this on the NeXT ColorStation, everything is dithered, and most colors
>probably won't be represented.

I find this complaint to be a little unreasonable. If very subtle color
reproduction is an imprrtant requirement for your application, you should get
some hardware that supports that.

--
Matt Emerson
matt@karazm.math.uh.edu