what’s really going on in ProRes? (or 10bit 4:2:2: uncompressed)?

[Bj Ahlen]

ProRes 422 colors in After Effects

[Dennis Couzin]

Josh Litle: “They are (in theory) mathematical operations based on the actual pixel values present in the files.”

They are mathematical operations, but unfortunately they are not both based on the actual pixel values present in the files. The uncompressed 10-bit 4:2:2 file contains actual pixel values. (I’ve viewed and played with the values for uncompressed 8-bit in a binary editor and it’s fun.) But the ProRes file does not contain actual pixel values. That file needs to be interpreted (decoded) to produce pixel values. The decoder can play games with little details like clipping, tone compression, even gamma.

In line with similar experiments I’ve done, I suggest you operate on a grey scale and read the RGB values (in Photoshop) after each step. At least you’ll determine the nature of the difference. Then you must determine if it’s real or an artifact of your tools.