oz differencing prototype gallery

>>here.

After finding a charming collection of chalkboard notes by Pat Hanrahan, I finally understand how Photoshop determines the values in a matrix of pixels resulting from the composite of two transparent layers. Then thinking like an optical printer (the person, not the machine) and tossing some ideas around with Adam Savje, I put together this gallery of image showing the pixels which are different between the original and derived frames.

Rebecca maintains the dream that we will show the frame that would be added to the DVD frame to reconstitute the original.
This is a harder problem. More later.