User Manual

–
Difference: Difference looks at the color information in each channel and subtracts
the foreground color values from the background color values or the background
from the foreground, depending on which has the greater brightness value. Merging
with white inverts the color. Merging with black produces no change.
–
Exclusion: Exclusion creates an effect similar to but lower in contrast than the
Difference mode. Merging with white inverts the base color values. Merging with
black produces no change.
–
Hue: Hue creates a result color with the luminance and saturation of the background
color values and the hue of the foreground color values.
–
Saturation: Saturation creates a result color with the luminance and hue of the base
color and the saturation of the blend color.
–
Color: Color creates a result color with the luminance of the background color value
and the hue and saturation of the foreground. This preserves the gray levels in the
image and is useful for coloring monochrome images.
–
Luminosity: Luminosity creates a color with the hue and saturation of the
background color and the luminance of the foreground color. This mode creates an
inverse effect from that of the Color mode.
 Operator Modes: This menu is used to select the Operation Mode of the merge. It
determines how the foreground and background are combined to produce a result.
This drop-down menu is visible only when the Merge node’s Apply Mode is set to
either Normal or Screen.
NOTE: For an excellent description of the math underlying the Operation
modes, read “Compositing Digital Images,” Porter, T., and T. Duff, SIGGRAPH
84 proceedings, pages 253-259. Essentially, the math is as described below.
TIP: Some modes not listed in the Operator drop-down menu (Under, In, Held
In, Below) are easily obtained by swapping the foreground and background
inputs and choosing a corresponding mode.
The formula used to combine pixels in the merge is always fg * x + bg * y. The different
operations determine exactly what x and y are, as shown in the description for
each mode.
The Operator modes are as follows:
–
Over: The Over mode adds the foreground layer to the background layer by
replacing the pixels in the background with the pixels from the Z wherever the
foreground’s Alpha channel is greater than 1.
x = 1, y = 1-[foreground Alpha]
–
In: The In mode multiplies the Alpha channel of the background input against the
pixels in the foreground. The color channels of the foreground input are ignored.
Only pixels from the foreground are seen in the final output. This essentially clips the
foreground using the mask from the background.
x = [background Alpha], y = 0
Chapter – 107 Tracker Nodes 2400