This kind of advice lacks some practically example in my eyes like the one to separate shadows: render one with and one without shadow: the difference is the shadow. I don´t have know of any blend mode in any raster image processor I own that will display only the shadow in the end.
Cheers
Frank
This has no pertinence to the original post (sorry), but maybe interesting, to separate a shadow from the background using Falcon this is what I've been doing (ymmv)...
1. render scene with no object, but with its shadow only (render tag) onto a background.
2. render background without the object or its shadow.
3. take both renders into Photoshop, each it's own layer and do an apply image between the two with blending mode = divide
The result is the shadow on a white (or almost white) background, which can then be extracted various ways.
note: I believe its not mathematically/theoretically equivalent - but its very usable in my experience.
All that being said, I would like a solution to render out some separate layers (background, shadow, object, clown etc.) using Falcon render engine.
--shift studio.