Modifying alpha channels is probably one of the things I do most when compositing. I’ve found Nuke’s Erode and Dialate nodes to be a bit too limiting and slow for many of these operations. So I made this lightweight tool for growing and shrinking the alpha channel. It works well for both small adjustments, like “leaning” the center of a gradient slightly towards one side, and big modifications.
☢️ Available on Nukepedia here
Also useful for things such as:
- Despotting a key
- Smoothing out jagged edges
- Making big mask expansions/contractions
- Pre-processing alpha for edge extension
Changelog
v1.1
- Fixed a bug that caused the alpha to change wrongly when
weight < 0even ifhardness = 0 - Improved accuracy especially when dealing with large, blurry areas
How to use
First you “prep” the alpha channel to only show what you want to use as a base:
Then you “bend” the result of prep to grow or shrink and add some blur if needed:
Modifying a simple linear ramp illustrates how the hardness and weight knobs affect gradients:
Inner workings
Runs on Blur and Grade nodes so it’s simple and fast