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From: timothym@tekigm.UUCP (Timothy D Margeson)
Newsgroups: net.micro.pc,net.micro
Subject: IBM Graphics improvement
Message-ID: <579@tekigm.UUCP>
Date: Thu, 26-Sep-85 13:30:29 EDT
Article-I.D.: tekigm.579
Posted: Thu Sep 26 13:30:29 1985
Date-Received: Sun, 29-Sep-85 07:52:58 EDT
Distribution: net
Organization: Tektronix, Beaverton OR
Lines: 71
Xref: watmath net.micro.pc:5445 net.micro:12145

Just a short note about the way to do things in color....

In article <372@bbncc5.UUCP> sdyer@bbncc5.UUCP (Steve Dyer) writes:
>> Hmmm... 256 out of 32K colors on a standard PC color display?  Sounds
>> interesting.  I wonder if they're working on a higher resolution version
>> that would run on the EGS (256 by 350 pixels, perhaps?)
> 
>No, on a color composite video monitor or analog RGB display.  It's
>impossible to display more than 16 colors on an IBM-CGA-compatible
>monitor or 64 colors on an Enhanced Color Display: the RGB signals
>are digital, not analog, and there are only 4 separate inputs 
>(or 6, for the ECD).  
>-- 
>/Steve Dyer
>{harvard,seismo}!bbnccv!bbncc5!sdyer
>sdyer@bbncc5.ARPA


Well buddy, you are wrong. For one thing, the RGB inputs, if driven
strictly digital would yield only 8 colors, but with an I input, you
can get 16 colors (both cases include black).

The scheme, or method these others are using to obtain >16 colors is
simple in concept, a little more difficult in scope.   They are pulse
width modulating the different digital lines during the normal pixel
period (or slightly longer than normal, hence 256 bit res.).

This technique will yield MANY more color options on your normal RGBI
monitor.

If it is still not understood how this works, here is an example.

For normal operation (as an IBM color card does it), say we want to
put one violet pixel displayed on the screen. We simply turn on the
red and blue guns for 1 pixel time. Viola, violet is shown.

For this enhanced method, say we want to have a color somewhere between
the violet above and red. In this case we turn on the red gun for one
pixel time as above, BUT, we only turn the blue gun on for 1/2 a pixel
time. This results in our eyes perceiving red-violet in stead of what
we saw above.

IBM Color:        __________
	  R _____|          |______

	  G _______________________
		  __________
          B _____|          |______
                  __________
          I _____|          |______   To give light violet or dim violet.

Improved:         __________
	  R _____|          |______

	  G _______________________
		     _____
          B ________|     |________
		  __________
          I _____|          |______   This line is probably modulated also.


So, I hope you can understand this method better now.




-- 
Tim Margeson (206)253-5240
tektronix!tekigm!timothym                   @@   'Who said that?'  
PO Box 3500  d/s C1-465
Vancouver, WA. 98665


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