Apple Shake 4 - Manual (Page 861)

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Filters
The filter nodes in Shake not only enable simple image
manipulation—they also provide numerous ways to
modify alpha channel data, allowing you to create useful
images for masking functions.
About Filters
While color corrections change the value of an individual pixel according to a
mathematical equation (for example, *2, -.5, and so on), filters calculate the new value
of a pixel by examining its neighbors, and passing it through what is called a spatial
filter. Classic filter functions are blur, image sharpen, emboss, and median. You can also
create your own unique filters, of any resolution, with the Convolve node. Spatial filters
are also applied when a geometrically transformed image is resampled—for example,
following a Scale or Rotate node.
Masking Filters
When you use an image to control the amount of filtering, you should use the multi-
input image-based filters such as IBlur, ISharpen, IRBlur, rather than simply masking the
effect. Using image-based filter nodes instead of mask inputs will slow down
processing, but the resulting effect will be ofs higher quality.
In the following example, a Text node is attached to a Blur node. A Ramp node attached
to the Blur mask input acts as a control image to modify the blur effect.