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The effect that each blend mode has on overlapping layers depends on the range of color
values in each layer. The red, green, and blue channels in each overlapping pixel are
mathematically combined to yield the final image.
These value ranges can be described as blacks, midrange values, or whites. These regions
are loosely illustrated by the chart below.
Blacks
Whites
Midrange color values
For example, the Multiply blend mode renders color values that fall into the white areas
of an image transparent, while the black areas of the image are left alone. All midrange
color values become translucent, with colors in the lighter end of the scale becoming
more transparent than the colors in the darker end of the scale.
Group Blend Modes
Blend modes work differently depending on whether they’re used with groups or layers.
In particular, the Pass Through blend mode is available only for groups.
Pass Through
When a group is set to Pass Through, each layer is blended with all layers and groups
that appear underneath it in the Layers list. In this example, the Swirls layer is set to Stencil
Luma, and the Fishes layer is set to Add.
293Chapter 7 Basic Compositing