The Add and Subtract blending modes
In the Add blending mode, the foreground is added to each corresponding background pixel. This mode is commutative, and the node's input order doesn’t matter. Values over 1 are trimmed. It adds white values from the foreground and background together.
Whereas in the Subtract blending mode, the Foreground input value will be subtracted from each corresponding background pixel. If the outcome of the subtraction is less than 0, the value is restricted to 0 and turns the result completely black. This is a non-commutative blending mode.
In this mode, the white portion of the foreground layer is subtracted from the background.
You can return to the Grayscale height value section in this chapter to see how these modes work in practice. This is a commutative blending mode.
