By John Ruttenberg

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.

Lighten & Darken Example

Right is a background layer for this example.

Left is a top layer.

Lighten Mode
Keeps only the lighter pixels from the top layer. Since the word black is at least as dark everywhere than the lower gradient layer, it doesn't make the blend.

Darken Mode
Keeps only the darker pixels from the top layer. The word white is everywhere at least as light as the background layer, it doesn't make the blend.

Color & Luminosity Blends
Right is a background layer for this example.

Left is a top layer for this example.

Color Blend
The words white and black are both neutral in terms of color. So in color blending mode, they have the effect of neutralizing the background. The word red is, well, red, so it blends by making everything it covers red.

Luminosity Blend
In luminosity blending mode, the contrast comes from the upper layer. The words black and white have the effect of removing color from the blend because there can be no color when luminosity is either completely dark or white. The word red is roughly neutral in terms of brightness and so it picks up the underlying color and imparting a neutral brightness to the blend.

I use these four blending modes more than any others by far. To show why, I'm going to walk through the processing of this image. Shown at the top is the final version. Shown right is the original. In order to correct it, I'm going to break the problem into two separate subproblems: Make the best B&W conversion I can which will give me the contrast I want, and then worry about color.

Well, I cheated a little. I used As Shot for Color Balance in raw conversion instead of being more more careful. This results in a blueish cast and overly magenta skin tones. In actual practice, I would have used custom color balance to make some point on his shirt neutral. But I wanted to expose both color and contrast color corrections for the purposes of this tutorial.