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656 Chapter 23 Color Correction
MDiv
The MDiv node divides the color channels by the alpha channel.
When you color correct a rendered (premultiplied) image, first apply an MDiv node to
the image to make the image a non-premultiplied image, perform the color correction,
and then add an MMult node to return the image to its premultiplied state. For more
information on premultiplication, see “A
bout Premultiplication and Compositing” on
page 421.
Parameters
This node displays the following control in the Parameters tab:
ignoreZero
Tells Shake to ignore pixels with an alpha value of 0.
• 0 = Divide entire image.
• 1 = Ignore zero-value pixels.
MMult
The MMult node multiplies the color channels by the matte.
This node is used to premultiply an image. When compositing with the Over node,
Shake expects all images to be premultiplied. Premultiplication is usually automatic
with 3D-rendered images, but not for scanned images. Also, use this node to color
correct a 3D-rendered image. Add an MDiv node to the image, perform your color
corrections, and then add an MMult node into an Over operation. For more information
on premultiplication, see “A
bout Premultiplication and Compositing” on page 421.
Note: You can also choose to not insert a MMult node, and instead enable preMultiply
in the Over node’s parameters.
Parameters
This node displays the following control in the Parameters tab:
ignoreZero
Tells Shake to ignore pixels with an alpha value of 0.
• 0 = Multiplies entire image.
• 1 = Ignore zero-value pixels.