Apple Shake 4 - Manual (Page 658)

658 Chapter 23 Color Correction
channels
The channels to be set.
value
The value of the channel.
SetAlpha
The SetAlpha node is simply a macro for Set and Crop that sets the alpha to 1 by
default. It exists because in the Infinite Workspace, color corrections extend beyond the
frame of an image. By using the Crop in the macro, the Set node is cut off, making the
image ready for transformations.
To remove the alpha channel from an image (turn an RGBA image into an RGB image),
set the alpha value to 0.
Parameters
This node displays the following control in the Parameters tab:
alpha
From 0 to 1, this is the alpha value of the output image. By default, it is 1.
SetBGColor
The SetBGColor node sets selected channels to the selected color outside of the
Domain of Definition (DOD). For example, if you create an Image–RGrad, the green
DOD box appears around the RGrad image in the Viewer. Everything outside of the
DOD is understood to be black, and therefore does not have to be computed. To
change the area outside of the DOD, attach a SetBGColor to the node and change the
color.
This node is often used for adjusting keys, as the keyer may be pulling a bluescreen,
and therefore assigns the area outside of the DOD, which is black, as an opaque
foreground. If the element is scaled down and composited, you do not see the
background. To correct this, insert a SetBGColor before the keyed element is placed in
the composite, for example, ChromaKey > SetBGColor > Scale > Over.