Booleans Operations Problems (Or not)

Hey guys,

I'm migrating from After Effects to Fusion and I'm facing some issues that are driving me crazy. In some tests to understand the ChannelBooleans tool the results of the alpha channel copy operation do not make sense to me. If I copy the alpha channel from one node to another the result is weird.

I have an ellipse mask in a BG node, so i get this node into the boolean to copy its alpha channel to the GREEN BG, but the result is a semi-transparent area even if the resulting alpha channel is pure black and white. what am I doing wrong ?

(sorry the bad english)

Yeah so you're seeing an unpremultiplied image there. In a program like AE you always see alpha channels premultiplied, but in nodal compositors like Fusion / Nuke you have to manually premultiply the image somewhere. This gives you the ability to perform operations like color correction in an unpremultiplied state, which is useful in a variety of situations.

Throw an "Alpha Multiply" node in the chain after your channel boolean and take a look at that.

Also, to read up on premultiplication:

https://learn.foundry.com/nuke/8.0/cont ... tions.html
https://www.schoolofmotion.com/blog/premultiplication/

Yeah so you're seeing an unpremultiplied image there. In a program like AE you always see alpha channels premultiplied, but in nodal compositors like Fusion / Nuke you have to manually premultiply the image somewhere. This gives you the ability to perform operations like color correction in an unpremultiplied state, which is useful in a variety of situations.

Throw an "Alpha Multiply" node in the chain after your channel boolean and take a look at that.

Also, to read up on premultiplication:

Man! That's it ! Many thanks for the reply and for the great links !