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From: gerhard@cs.arizona.edu (Gerhard Mehldau)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Query:  question about color on the mac...
Message-ID: <23451@megaron.cs.arizona.edu>
Date: 24 Jul 90 17:23:32 GMT
References: <10754@odin.corp.sgi.com> <23410@megaron.cs.arizona.edu> <139442@sun.Eng.Sun.COM>
Organization: U of Arizona CS Dept, Tucson
Lines: 47

In article <139442@sun.Eng.Sun.COM>, johnston@adhawk.Eng.Sun.COM (Scott Johnston) writes:

> >The code for the color table/palette stuff should
> >look like this (note that this code requires 32-Bit
> >QuickDraw to be installed):

> >CTabHandle gTable;
> >PaletteHandle gPalette;
> >gTable = GetCTable(kColorTable);	    /* read in from resource file */
> >gPalette = NewPalette((*gTable)->ctSize+1,gTable,pmTolerant+pmExplicit,0);
> >SetPalette((WindowPtr)(-1),gPalette,TRUE);  /* make default palette */

> I have been flailing miserably with this, too, so correct me if
> I am wrong.  Isn't the color table created with the above set of 
> commands still dependent upon the underlying device CLUT?  And
> this device CLUT has not changed?  So, the way I understand it,
> the Color Manager will attempt to find the closest RGB matches
> between this newly created CLUT and the device CLUT.

  No, it doesn't.  If you set the tolerance to 'pmTolerant+pmExplicit',
  the palette manager will do all the ugly work of modifying the CLUT
  for you - and, even better, will switch back to the old CLUT when
  your application quits.  And you do get the exact colors you want
  in exactly the locations you requested them.

> What if you wanted to do 256-tone Gray Scale?  Wouldn't you need
> to go in and modify the device's CLUT directly in order to get
> this wide range of grays?

  Again, no.  I've been using the above code to create a palette
  with a 128-level grayscale, and 128 colors (for an image processing
  application), and it works just fine...

> Just worth mentioning:  modifying the device CLUT gets ugly.

  It certainly does.  I should know - this was also one of my
  earlier attempts at solving the problem (before 32-Bit QuickDraw
  was released).

> sj

- Gerhard
-- 
-> Gerhard Mehldau
   Dept. of Computer Science	internet: gerhard@cs.arizona.edu
   University of Arizona	uucp:     {cmcl2,noao,uunet}!arizona!gerhard
   Tucson, AZ 85721, U.S.A.	at&t:     +1 (602) 621-4632