User Manual

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Hard Light: Hard Light multiplies or screens the color values of the foreground
image, depending on the color values of the background image. The effect is similar
to shining a harsh spotlight on the image.
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Color Dodge: Color Dodge uses the foreground’s color values to brighten the
background image. This is similar to the photographic dark room technique of
dodging by reducing the exposure of an area of a print.
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Color Burn: Color Burn uses the foreground’s color values to darken the background
image. This is similar to the photographic dark room technique of burning by
increasing the exposure of an area of a print.
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Darken: Darken looks at the color information in each channel and selects the
background or foreground image’s color value, whichever is darker, as the result
color. Pixels lighter than the merged colors are replaced, and pixels darker than the
merged color do not change.
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Lighten: Lighten looks at the color information in each channel and selects the
background or foreground image’s color values, whichever is lighter, as the result
color value. Pixels darker than the merged color are replaced, and pixels lighter than
the merged color do not change.
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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.
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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.
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Hue: Hue creates a result color with the luminance and saturation of the background
color values and the hue of the foreground color values.
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Saturation: Saturation creates a result color with the luminance and hue of the base
color and the saturation of the blend color.
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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 result color with the hue and saturation of the
background color values and the luminance of the foreground color values. 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.
Changing the Operation mode changes how the foreground and background are
combined to produce a result. This pop-up menu is visible only when the Merge node’s
Apply mode is set to either Normal or Screen.
For an excellent description of the math underlying the Operation modes, read
Compositing Digital Images, Porter, Thomas, and T. Duff, ACM SIGGRAPH Computer
Graphics proceedings, 1984, pages 253-259. Essentially, the math is as described
below. Note that 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
(with Command-T or Ctrl-T) 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.
Chapter – 86 Composite Nodes 1912