Apple Shake 4 - Manual (Page 708)

708 Chapter 24 Keying
The transparency of the foreground is measured by calculating the difference
between the dominant screen color (blue by default, otherwise the value of the
screenColour parameter) and a weighted average of the other two colors (red
and green).
With the example of a cyan screen, there is a greater difference between the blue
and the red than between the blue and the green, since cyan has more green than
red. Setting the balance to 0 forces Keylight to ignore the second-most dominant
color in the screen, which is green in the example. When set to 1, the weakest screen
color (red) is ignored. There are three controls to tune the low, medium, and
highlight ranges.
• shadowGain, midtoneGain, and highlightGain: Located in the fineControl subtree,
these parameters let you increase the gain to make the main matte more
transparent. This tends to tint the edges the opposite of the screen color—for
bluescreens edges become yellow. Decrease the gain to make the main matte more
opaque.
Note: You can lower the highlightGain parameter (to approximately -0.25) to
strengthen weak areas in the interior of a mask that are due to green or blue casts in
the highlights of foreground subjects in float images.
• midTonesAt: Located in the fineControl subtree, this parameter adjusts the effect of
the balance and gain parameters by changing the level of the midtones they use. For
example, If you are working on a dark shot, you may want to set the midtone level to
a dark gray to make the controls differentiate between tones that would otherwise
be considered shadows.
replaceColour
Spill can be replaced by the replaceColour. This occurs only in the opaque areas of the
holdout matte. This is useful with blue areas in the foreground that you want to keep
blue and opaque. The replaceColour is therefore blue.
fgMult
Allows color correction on the foreground element. This exactly mimics the Shake
Brightness node.
fgGamma
Applies a gamma correction to the foreground element. This exactly mimics the Shake
Gamma node.
saturation
Applies a saturation correction to the foreground element. This exactly mimics the
Shake Saturation node.