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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!uccba!uceng!mfinegan
From: mfinegan@uceng.UC.EDU (michael k finegan)
Newsgroups: comp.sys.ibm.pc,comp.graphics
Subject: Re: VGA palette & memory: HOW??
Summary: 256 color <> 256 grey scale
Keywords: vga, palette
Message-ID: <643@uceng.UC.EDU>
Date: 2 Feb 89 16:50:15 GMT
References: <109@jarthur.Claremont.EDU> <15102@oberon.USC.EDU>
Distribution: na
Organization: Univ. of Cincinnati, College of Engg.
Lines: 17

In article <15102@oberon.USC.EDU>, annala@neuro.usc.edu (A J Annala) writes:
> I thought the CGA adaptor was capable of 256 simultaneous colors ... or
		VGA
> Can it generate 256 grey scales ... 256 independently controlled colors ...
  While 256 colors are available in 320 x 200 (columns x rows) mode, the
  IBM VGA uses 6 bit DAC's, so it is impossible to get more than 64 grey
  shades, since grey implies R = G = B, leaving 0 to 2^6 - 1 as possible
  unique LUT locations ...
  An excellent reference (complete w/ source code to program palette's,
  etc., etc.) is : Programmer's Guide to PC & PS/2 VIDEO SYSTEMS by
  Richard Wilton (Microsoft Press). I had to use a current ROM BIOS
  reference (Ray Duncan -- also Microsoft Press) for the VGA palette
  save/load routines, but it was fast enough for what I wanted ...

					Hope this helps,
					Mike Finegan
					mfinegan@uceng.uc.edu