Blend If
A control that makes a layer's visibility depend on the brightness values of the layer itself or the layers below.
Measured in
levels (0-255)
In depth
Blend If produces a mask automatically from tonal values rather than from painting, which makes it exceptionally fast for restricting an effect to highlights or shadows. Splitting the slider handles feathers the transition, avoiding the hard edges that an unsplit threshold produces.
Examples in practice
Setting a warming layer to blend only where the underlying image is bright confines it to the highlights automatically.