This section covers the blending modes lighten, darken, luminosity, and color. Here are definitions of these blending modes when A is layered on top of B with the given blending mode:
- Lighten: Where A is lighter than B use pixels from A; otherwise, use pixels from B.
- Darken: Where A is darker than B use pixels from A; otherwise, use pixels from B.
- Color: Derive color values from A and luminosity from B.
- Luminosity: Derive luminosity from A and color from B.
The distinction of luminosity versus color is easiest to understand in the L.A.B. color model where luminosity has it's own channel. In L.A.B. a color blend takes the L channel from B while retaining the A and B channels from A. A luminosity blend does the opposite.
Note that in some important sense, Lighten doesn't actually make anything lighter. It merely chooses the lighter corresponding pixel from the two layers. If B is lighter than A the blend does nothing. Similarly, Darken may not actually make anything darker, it only selects the darker of the two layers. Dan Margulis remarks that really Lighten means don't darken.