Difference blend mode subtracts layers and takes the absolute value, making matching areas black and differing areas bright

Difference: f(a,b) = |a-b|. Since this takes the absolute value, the result is never negative. Blending identical layers gives pure black (all differences are zero). Blending with black produces no change (subtracting 0). Blending with white inverts the image (all values become 1-a). The most practical use is alignment verification: place two copies of similar images in Difference mode — if they are perfectly aligned, the result is pure black; any offset shows up as visible patterns. Exclusion is the same idea but with lower contrast.

Examples

Difference of two identical frames: pure black. Slightly offset copies: reveals motion/displacement as glowing edges. White top layer: inverts the base. Black top layer: no change.

Assessment

A VJ wants to detect where two video frames differ. Which blend mode should they use, and what does the resulting image show? What does pure black mean in that output?