Path: utzoo!mnetor!uunet!husc6!rutgers!mtunx!lzaz!mtunb!dmt
From: dmt@mtunb.ATT.COM (Dave Tutelman)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MCGA/VGA 320X200 256 Color mode
Message-ID: <1207@mtunb.ATT.COM>
Date: 28 Apr 88 22:17:44 GMT
References: <496@sdics.ucsd.EDU> <45900124@uxe.cso.uiuc.edu>
Reply-To: dmt@mtunb.UUCP (Dave Tutelman)
Organization: AT&T Information Systems - Lincroft, NJ
Lines: 47

I originally mailed this, but it bounced.  However, the posting may not
be entirely inappropriate...

Steve Lau wrote:
>>    It may be low-res, but the number of colors available more than makes
>>up for the difference. By blending many of the colors the appearance of
>>a higher resolution can be generated.

In article <45900124@uxe.cso.uiuc.edu> Doug McDonald responded:
>
>Steve, I don't see your point. I certainly see how I can take a high res
>16 color display and get the impression of a larger palette by dithering,
>but I don't see how low res can be fixed. How would you simulate 80
>column text on a 320 pixel wide display? Your statement isn't logical.

Actually, logical or not, it has a certain truth.  

Doug talks about using 
	SPACIAL dithering to make up for coarse COLOR quantization.
Think about the converse, using
	COLOR dithering to make up for coarse SPACIAL quantization.

What this CAN do is eliminate the "jaggies" from sloped edges on the
screen, by modulating ("dithering") the color of each coarse pixel
to weight each color by the amount the edge protrudes into the coarse pixel.
What it CAN'T do, as Doug correctly points out, is 80-column text.

So why use it at all?  To give the APPEARANCE of high resolution in
a picture that:
   -	has low detail, so you don't need the REAL spacial resolution,
	but can afford to simulate it with color modulation ("dithering").
   -	requires smooth color transitions (shading), thus requiring
	more colors than the video RAM could support at high res.
Either color dither or spacial dither would suit such images when viewed
at a distance, and either technique falls apart when viewed close up.
But the color dither seems to work better than spacial dither at
middle distances.  And it's especially good at continuous color transition
across a "curved" surface (2D representation).

Hope this helps.

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