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From: marmoset@mondo.engin.umich.edu (Dave Walker)
Newsgroups: comp.sys.mac.misc
Subject: Re: 24-bit color
Message-ID: <1990Dec5.165012.24188@engin.umich.edu>
Date: 5 Dec 90 16:50:12 GMT
References: <6110@crash.cts.com>
Sender: news@engin.umich.edu (CAEN Netnews)
Organization: Computer Aided Engineering Network (CAEN), University of Michigan
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In article <6110@crash.cts.com> bill@pro-gateway.cts.com (Bill Long, SysOp) writes:
>I'm an Apple II user and try to somewhat keep up with the Mac world, and I
>have a couple of questions about 24-bit graphics.
>
>1) Why is 24-bit better than 32-bit?
>
Actually, it's not.  The confusion arises because people sometimes use
24-bit and 32-bit to describe the same products.   Apple's 32-bit
Quickdraw system software supports pixels with as much as 32 bits of
information each.  These pixels are broken down as follows:

-8 bits of red
-8 bits of green
-8 bits of blue
-8 undefined bits (known as the "alpha channel") which can be used for
 video compositing, transparency information, etc.  Some video overlaying
 hardware and image manipulation programs use the alpha channel for their
 own purposes.

Most video boards currently ownly deal with the red, green, and blue channels.

>2) How many of the 16 million colors can be on-screen at once?
>
It depends on your monitor's size.  A 640X480 monitor, like Apple's 13" 
High-Resolution Color Monitor, can display 640*480= 307200 colors,
while a 1024X768 19" monitor could display 1024*768=  786432 colors.

>Thanx...
>
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+------------------------------------------------------------------------+
| Dave Walker, Detroit Art Services (DAS)                                |
| marmoset@ub.cc.umich.edu                 "I don't read, I just guess"  |
| marmoset@mondo.engin.umich.edu       -Happy Mondays, "Wrote For Luck"  |
+------------------------------------------------------------------------+