Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!emory!mephisto!mcnc!rti!bcw
From: bcw@rti.UUCP (Bruce Wright)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Super Duper VGA boards
Summary: Video Lookup Tables (LUT)
Message-ID: <3300@rti.UUCP>
Date: 1 Dec 89 02:04:51 GMT
References: <8911250811.AA26716@cie.uoregon.edu> <10401@attctc.Dallas.TX.US> <4033@peora.ccur.com>
Organization: Research Triangle Institute, RTP, NC
Lines: 30

In article <4033@peora.ccur.com>, joel@peora.ccur.com (Joel Upchurch) writes:
> It seems to me that if a board supports 16-bits/pixel that it would be
> better to have the colors map directly rather than going through a
> mapping table. With 5 bits each for red, green and blue that would
> give you 32k colors to work with one bit left over. This would eliminate
> the overhead of setting up the color mapping table as well the
> hardware to do the mapping.

This is certainly true for some applications, but if you want to do
image processing it can be *VERY* useful to be able to play around 
with a video lookup table.  For example, you can quickly and easily
highlight a portion of the image that has a particular range of values,
change the brightness mapping scale to provide better definition,
and so forth.  It saves having to manipulate the image in your program
and reload it onto the screen (saving both execution time and programming
time, at least for large classes of display devices).

Also, if the predefined colors aren't enough (for example, many images
are processed with between 256 and 2048 shades of grey, which exceeds
what you can get with 5 bits each for R,G,B = 32 shades of grey unless
you get a monitor that can combine the signals from more than one of
the color guns), you can always re-arrange the color map to get more
of the types of colors you need and fewer of the ones you don't need.

Again, however, you are right that for a good many PC applications
(=text, charts, "business graphics", etc) 32k colors with 5 bits each
for R,G, and B is more than enough.  For that matter, for many PC
applications 16 or 4 or even 2 is enough!

					Bruce C. Wright