Control The Mix With Blend Modes
As well as controlling the amount channels are blended, you can control the way they’re blended by using blending modes. Blend modes determine how new values are mixed with old values. There are dozens of blend modes to choose from.
As color adjustment is achieved by altering the luminance (light and dark) values of select channels (Channels create but don’t contain color or saturation), when it comes to blending channels, you can limit the number of blend modes you use to those that affect tone. Five are particularly useful—Lighten, Screen, Darken, Multiply and Luminosity.
Lighten displays the lightest values of both This Layer and the Underlying Layer; its neutral color is black (you can’t lighten with black).
Screen multiplies the inverse values of the pixels’ lightness or darkness. It’s like registering the same image in the same location from two projectors. Think of it as industrial-strength lightening. Its neutral color is black (you can’t lighten with black). Screen can do wonders for opening up deep shadows. It has a tendency to blow out highlights. Use a contrast mask to remove the effect from highlights.
Darken displays the darkest values of both This Layer and the Under-lying Layer; its neutral color is white (you can’t darken with white).
Multiply multiplies the values of the pixels on both layers and then divides by 255. It’s like registering two identical transparencies on a light table. Think of it as industrial-strength darkening. Its neutral color is white (you can’t darken with white). Multiply can do wonders for reclaiming subtle highlight detail. It has a tendency to block up shadows. Use a contrast mask to remove the effect from shadows.
Luminosity combines the luminance values of This Layer with the hue and saturation of the Underlying Layer; it has no neutral color.