Chapter: Compositing Tools and Techniques
Topic: Scripting or Expressions
Similar to setmatte, but with much more control. Use ?compound alpha Arithmetic? to make boolean in your rgb image. Like the operator ?multiply? in the logicop of flame but the final result is a rbga image. You can also use this operator with a puzzle matte to isolate a part of a 3d render using a rgb channel. You can also animate the opacity of this effect in the operator menu.