Difference keying can be an extremely powerful technique to generate mattes, especially rough mattes, very quickly. But the Nuke Keyer version of this is pretty bad and unintuitive. And while building out a difference keyer using a merge and luma keyer isn't hard, I thought I'd put together a quick gizmo that makes it a no brainer. 

The clean plate and footage plate need to be stabilzed or matchmoved together and you should degrain your footage and plate before piping them in.  

Footage

Plate

Final

This gizmo subtracts the clean plate from the footage plate, then adds together the absolute value of all the channels and pumps the result into the alpha channel. 

V1.1 updated the math to get rid of banding.

v1.2 created the ability to blur/soften the clean plate and hero plate seperately. updated info and interface.

v1.3 added colorspace changing options and a patch holes slider.

Any suggestions, please let me know at [email protected]

Atlanta Georiga based compositor and VFX | www.itaki.com