Overlay and the Light Modes

Overlay and the Light Modes

Overlay uses Screen or Multiply, depending on the background
pixel value. Above a threshold of 50% gray (or .5
in normalized terms), Screen occurs, and below the threshold,
Multiply. Hard Light operates similarly, instead using
the top layer to determine whether to screen or multiply,
so the two are inverse effects.
These modes, along with Linear and Vivid Light, can be
most useful for combining a layer that is predominantly
color with another layer that is predominantly luminance,
or contrast detail (Figure 3.30). Much of the lava texturing
in the Level 4 sequence of Spy Kids 3-D was created by using
Hard Light to combine a hand-painted color heat map
with moving fractal noise patterns.

Difference

Difference inverts a background pixel in proportion to the
foreground pixel. It can help you line up two identical layers,
which is handy while working even if you rarely use it
for fi nal output