Compositing with alpha

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#1859

From: Grant J. Munsey
Date: Fri, 20 Nov 1992 23:26

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Anyone know what the formula is for determining the value of a pixel
when a color is composited into it. I'm talking about the case where
both pixels have rgb and alpha channels. I understand how to do the
color components but I'm stumped on what the final alpha value is. An
example take a color red with .5 alpha {1,0,0,.5} and composite it into
a pixel with gray and .2 alpha {.5,.5,.5,.2} what is the result {?,?,?,?}.
----
Grant Munsey, Mainticore, Inc. (408)252-1135
grant@Manticore.COM,  uunet!ub-gate!gouche!grant   NeXTMail ok.

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Path: arc1-ca.pugleaf.net!sparky!uunet!elroy.jpl.nasa.gov!ames!pacbell.com!UB.com!gouche!Manticore.COM
From: grant@Manticore.COM (Grant J. Munsey)
Newsgroups: comp.sys.next.programmer
Subject: Compositing with alpha
Message-ID: <359@gouche.UUCP>
Date: 20 Nov 92 23:26:10 GMT
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