Apple Shake 4 - Manual (Page 709)

Chapter 24 Keying 709
colourspace
Keylight models the interaction of the blue/green light from the screen with the
foreground elements. For these calculations to work correctly, you need to specify how
pixel values relate to light levels. This is the function of the colourspace menu.
Therefore, with Cineon plates (or other logarithmic files) you have the option to pull
the key with or without a Delog operator before the key pull.
• log: Color spaces are designed so that a constant difference in pixel values
represents a fixed brightness difference. For example, in the Cineon 10-bit file format,
a difference of 90 between two pixels corresponds to one pixel being twice as bright
as the other.
• linear: This color space has the brightness of a pixel proportional to its value. A pixel
at 128 is twice as bright as a pixel at 64, for example.
• video: Color space has a more complicated relationship, but the brightness is
approximately proportional to the pixel value raised to the power of 2.2.
plumbing
The subparameters in the plumbing subtree allow you to adjust how the input images
are used to create the final output image and matte.
• useHoldOutMatte: If the third image input is used for a holdout matte, toggles the
holdout matte on and off.
• holdOutChannel: Specifies which channel of the image is being used as the holdout
matte.
• useGarbageMatte: If the fourth image input is used for a garbage matte, this button
toggles the garbage matte on and off.
• garbageChannel: Specifies which channel of the image is being used as the garbage
matte.
• bgColor: Either pulls a key on the area outside of the frame (0), or asserts the
background as the background color (for example, usually black).
• clipMode: Sets the output resolution of the node—either the foreground image (1)
or the background image (0) resolution.
LumaKey
The LumaKey node creates a key in the alpha channels based on overall luminance.
Values below loVal are set to zero, and values above hiVal are set to 1. Values in
between are ramped. You also have roll-off control, and an mMult toggle.
This is a fast way to place the luminance of an image into the alpha layer, but this
operation can also be done with a Reorder node set to rgbl.
Parameters
This node displays the following controls in the Parameters tab:
loVal
Any pixel below this value (as calculated by its luminance) turns black.