Screen blend mode lightens by inverting, multiplying, and inverting again — giving black transparency and white full brightening

Screen: f(a,b) = 1-(1-a)(1-b). This is the complement of Multiply: where Multiply always darkens, Screen always lightens or preserves. Where either layer is black (0), the result equals the other layer (identity). Where either layer is white (1), the result is white. Like Multiply, Screen is commutative. Conceptually, Screen is like projecting two slides onto the same screen: the combined light is always at least as bright as either source. Practical use: Screen a glow or flame element over a scene to add light without darkening anything.

Examples

Screen a 50% grey over a 50% grey: 1-(0.5)(0.5) = 0.75 — lighter than either. Screen white over anything: white. Screen black over anything: no change.

Assessment

Compute Screen for a=0.4, b=0.7. Compare to Multiply for the same values. Explain the relationship between the two formulas — why is Screen called the ‘inverse’ of Multiply?