CGTalk - using an image's alpha for another image

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smaug

02-26-2004, 09:10 PM

hi
i have come to a problem today with comp. in conbustion
but i couldnt find any real solution to this so can you help

i have an image sequence that i color corrected using a random value expression( a brightness contrast adjustment actually)

i have another layer that i assigned a discreet keyer to get a matte
what i want is to use the keyed images alpha as the first layers alpha so the brightness doesnt make the background layer(3th layer at the bottom)

any help?
thanks

tobiasth

03-01-2004, 08:54 AM

they are two solutions:

1. use the "set matte" operator.
2. use the "alpha arithmetic" operator.

both under Channels.

sometimes its helpful when you "nested" the layers you use for the alphachannel.

hope it works,
tobi

smaug

03-01-2004, 07:48 PM

yeah
set matte operator did the job
thanks a lot
:wip:

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