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From: cem@intelca.UUCP (Chuck McManis)
Newsgroups: net.micro.amiga
Subject: Re: Re: interlace mode
Message-ID: <200@intelca.UUCP>
Date: Wed, 29-Jan-86 11:17:15 EST
Article-I.D.: intelca.200
Posted: Wed Jan 29 11:17:15 1986
Date-Received: Sat, 1-Feb-86 03:41:21 EST
References: <1096@caip.RUTGERS.EDU>
Organization: Intel, Santa Clara, Ca.
Lines: 41

> ...
> some discussion about bits vs combinations etc
> ...
> 
> 	 Resolution, on the other hand, does not work this way. Inorder to
> double the resolution (display twice the number of pixels on the screen)
> one must double the screen memory (not just add another bit plane, as
> with doubling the number of colors).  In order to double the screen
> resolution the size of the bit planes must be doubled. In order to
> maintain the same display bandwidth (same screen memory size) this
> results in the need to cut the number of bit planes in half.  With the
> example sighted above doubling the resolution required reducing the
> number of bit planes from 4 to 2. Lossing 2 bit planes means cutting you
> color selection to 1/4 of its original size. Thus, the atari ST displays
> 16 colors in low resolution color mode and 4 colors in high resolution
> color mode.
> 	 
> John
> 
> p.s. Sorry if this simple minded discussion of bit planes bored you. As
> for my self, I find it fascanating.

You will note John that a common 'double' the resolution interpretation is
to double *both* X and Y resolutions. This actually displays 4 times the 
number of pixels on the screen. Now in the case of the Atari and the Amiga
they 'double' the resolution from 320 X 200 by only doubling the X direction
to 640. This does not help a lot of graphics applications that would really
like reasonably square pixels. The Amiga will display 640 X 400 (bringing 
it much closer to the 3:2 aspect ratio (or is it 4:3?) of the 'standard'
CRT, to a lot of people this is the only interpretation of the term when
applied to raster displays. Interestingly, the Amiga still displays 16
colors/pixel because it also cuts the bandwidth requirements in half.

--Chuck


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