User Manual

–
Held Out: Held Out is essentially the opposite of the In operation. The pixels in
the foreground image are multiplied against the inverted Alpha channel of the
background image. You can accomplish exactly the same result using the In
operation and a Matte Control node to invert the matte channel of the background
image.
x = 1-[background Alpha], y = 0
–
ATop: ATop places the foreground over the background only where the background
has a matte.
x = [background Alpha], y = 1-[foreground Alpha]
–
XOr: XOr combines the foreground with the background wherever either the
foreground or the background have a matte, but never where both have a matte.
x = 1-[background Alpha], y = 1-[foreground Alpha]
 Subtractive/Additive: This slider controls whether Fusion performs an Additive merge,
a Subtractive merge, or a blend of both. This slider defaults to Additive merging
for most operations, assuming the input images are premultiplied (which is usually
the case). If you don’t understand the difference between Additive and Subtractive
merging, here’s a quick explanation:
–
An Additive merge is necessary when the foreground image is premultiplied,
meaning that the pixels in the color channels have been multiplied by the pixels
in the Alpha channel. The result is that transparent pixels are always black since
any number multiplied by 0 always equals 0. This obscures the background (by
multiplying with the inverse of the foreground Alpha), and then simply adds the
pixels from the foreground.
–
A Subtractive merge is necessary if the foreground image is not premultiplied. The
compositing method is similar to an Additive merge, but the foreground image is first
multiplied by its Alpha to eliminate any background pixels outside the Alpha area.
In most software applications, you will find the Additive/Subtractive option displayed as
a simple checkbox. Fusion lets you blend between the Additive and Subtractive
versions of the merge operation, which is occasionally useful for dealing with problem
composites with edges that are calling attention to themselves as too bright or too dark.
For example, using a Subtractive setting on a premultiplied image may result in darker
edges. Using an Additive setting with a non-premultiplied image may result in
lightening the edges. By blending between Additive and Subtractive, you can tweak
the edge brightness to be just right for your situation.
Filter Method (Match Move)
Determines which filter to use to handle image transforms made using the Tracker node. This
menu appears only when the Operation Mode is set to Match Move.
 Box: This is a simple interpolation resize of the image.
 Linear: This uses a simplistic filter, which produces relatively clean and fast results.
 Quadratic: This filter produces a nominal result. It offers a good compromise between
speed and quality.
 Cubic: This produces better results with continuous-tone images but is slower than
Bi-Cubic. If the images have fine detail in them, the results may be blurrier than desired.
 Catmull-Rom: This produces good results with continuous-tone images that are resized
down. It produces sharp results with finely detailed images.
Chapter – 107 Tracker Nodes 2401