Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!jarthur!nntp-server.caltech.edu!madler
From: madler@nntp-server.caltech.edu (Mark Adler)
Newsgroups: comp.sys.next
Subject: Re: NeXTStation Color (again)
Message-ID: <1991Apr25.221324.3202@nntp-server.caltech.edu>
Date: 25 Apr 91 22:13:24 GMT
References: <1991Apr25.181814.19762@ux1.cso.uiuc.edu> <1991Apr25.195907.29367@ni.umd.edu>
Organization: California Institute of Technology, Pasadena
Lines: 31

In article <1991Apr25.195907.29367@ni.umd.edu> louie@sayshell.umd.edu (Louis A. Mamakos) writes:
>This can't possibly be this hard to understand.  The user-level model
>for color is you have 4 bits each R, G and B, plus 4 bits for the
>alpha channel.  Deep in the guts of the hardware there is a mapping
>function which takes the "ideal" RGB values and transforms them to
>accomodate the non-linearity of the phosphers on the screen.  This
>isn't something that user-level code gets to diddle or even see.
>
>User-accessable Color pallettes are a kludge anyway IMHO.  I think
>that its wonderful that you don't have to worry about screwing with
>them in the first place on the NeXT.

I agree that CLUT's are a kludge.  However, what people want to know
is if they can look at 256-gray level images on a (much cheaper than
NeXTdimension) color slab, without dithering.  (For example, 800x800
JPL images.)  The first question is, "can the hardware do it?".  The
second is "will the software let me?".  If those are "yes, no", then
the third question is "how can I get around it (there's always a way
for the persistent hacker)?".

There is a CLUT in the color slabs, but to answer the first question
you need to know if the chip has three 16x8 rams or one 4Kx24 ram to
feed the three 8 bit D/A converters.  This determines if the machine
is capable of 16 or 256 shades of gray.

Even if it is 4Kx24, the answer to the second question is no.  So an
answer to the first question is needed before hacking away at how to
get around the restrictions and answer question three.

Mark Adler
madler@pooh.caltech.edu