How I can subtract a blurry alpha channel from another alpha channel in the compositor?
First alpha channel
Second alpha channel
Desired result
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1 Answer
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1
You need nothing more then a Mix node set to Subtract with a factor of one.
To replicate your bottom image, plug your first image in to the first socket on the mix node, and the blurry image into the second socket.
*) When the substract operation is used,make sure to mark the "clamp" checkbox to avoid negative values in the result.
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1$\begingroup$ It should be noted that subtraction is only for where the geometry perfectly matches and does not overlap. Otherwise, use probability formula aka A+B-AB. lists.openimageio.org/pipermail/oiio-dev-openimageio.org/… $\endgroup$– troy_sJan 18, 2016 at 23:50