The Pseudo-Alpha compositor composites a foreground image against the background by creating an alpha channel for the foreground image based on the foreground image's upper-left-corner pixel. All pixels in the foreground image that use this color become transparent.
Pseudo Alpha compositing
Because only one pixel color becomes transparent, edges of the opaque areas in the foreground image are aliased. Use this method when the foreground image is a bitmap whose format does not have an alpha channel.
There are no setup options for this compositor.
There is also a Pseudo Alpha filter event.
To use the Pseudo Alpha Compositor: