Path: utzoo!attcan!utgpu!watmath!watserv1!magore
From: magore@watserv1.waterloo.edu (Mike Gore, Institute Computer Research - ICR)
Newsgroups: comp.graphics
Subject: Re: VGA Colors
Message-ID: <119@watserv1.waterloo.edu>
Date: 10 Nov 89 18:05:02 GMT
References: <824@uwm.edu>
Reply-To: magore@watserv1.waterloo.edu (Mike Gore, Institute Computer Research - ICR)
Organization: U. of Waterloo, Ontario
Lines: 38

Hi,

In article <824@uwm.edu> jrn@csd4.csd.uwm.edu (James Ray Norton) writes:
[ re: VGA palette ]
>I've got another question.
...
>      for i:=0 to 255 do
>         SetRGBPalette(i,i,i,i);
>
>I would assume that I should have gotten 256 varying shades of grey.
>But I didn't.  I got 4 sections of 64 shades of grey,  were each section
>had the same 64 colors.
>
>How would I get 256 DIFFERENT shades of grey?

	Although the DACs on each of THE R B G channels are 6 bits you can 
fudge the palettes to get a better aproximation the 64 with just a bit of color
offset for some entries. 

	If you keep each of the 64 palette entries for R G & B within
+/-1 of each other and then consider the sum of R G & B as the actual output 
you can get 192 values out of 256. This works because near output values of 0
the colors resulting from the offsets are so dark as not to be very visible 
and for high values of output the color offset does not contribute much to the 
overall brightness.
	I have used this method with good results. For better results
one should adapt the palette for the monitor being used since each
channel of R G & B on most all monitors have slightly differing transfer 
functions for each channel anyway. In otherwords given a pure gray signal you
will still likely get slight changes of color in the "grey" with just changes 
in brightness alone - tweeking the palette can avoid most of this.

Good luck!,

# Mike Gore, Technical Support, Institute for Computer Research
# Internet: magore@watserv1.waterloo.edu   or   magore@watserv1.uwaterloo.ca
# UUCP:     uunet!watmath!watserv1!magore
# These ideas/concepts do *not* imply views held by the University of Waterloo.