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From: bard@jessica.stanford.edu (David Hopper)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: NeXT/Amiga Flamage: Get a life.
Message-ID: <1991Apr10.043022.20442@leland.Stanford.EDU>
Date: 10 Apr 91 04:30:22 GMT
References: <10902@uwm.edu> <&5aGlabl1@cs.psu.edu> <1991Apr10.005729.22997@cunixf.cc.columbia.edu> <1991Apr10.035203.3854@mintaka.lcs.mit.edu>
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In article <1991Apr10.035203.3854@mintaka.lcs.mit.edu> rjc@geech.gnu.ai.mit.edu (Ray Cromwell) writes:

> From what I understand, alpha channel is transparency. I'm not used to
>it in a 2d sense, but in a high end z-buffered graphics system, Alpha
>channel specifies how much color to borrow from the pixel underneath.
>So if you have a blue sphere behind a red sphere, an alpha channel
>value of 128 (with 8 bits of alpha) specifies a 50% blending (im guessing
>here. I don't know how the real implementation of alpha works). So
>in theory, 50% of the color of the blue pixels would "show thru" the red's
>causing the red sphere to be partially transparent.

The Alpha channel also holds heirarchical information (i.e. which pixels
are above/below each other)-- using this with transparency, you can get
great effects like when you move an object behind a picture of a car,
for instance, you can see the object through the window; dimmed, as it
would be in real life.

>|n|   rjc@albert.ai.mit.edu   Amiga, the computer for the creative mind.  |n|

Dave Hopper      |     /// Anthro Creep  | Academic Info Resources, Stanford
                 |__  ///     .   .      | Macincrap/UNIX Consultant
bard@jessica.    |\\\///     Ia! Ia!     | -- Just remember: love is life, and
   Stanford.EDU  | \XX/  Shub-Niggurath! | hate is living death. :Black Sabbath