User Manual

While masks (or mattes) are connected via an input, they are actually applied “post effect,”
which means the node first applies its effect to the entire image, and then the mask is used to
limit the result by copying over unaffected image data from the input.
A Polygon node used as a mask to limit the Blur node’s effect.
Although many nodes support effects masking, there are a few where this type of mask does
not apply—notably Savers, Time nodes, and Resize, Scale, and Crop nodes.
TIP: Effects masks define the domain of definition (DoD) for that effect,
making it more efficient.
Pre-Masking Inputs
Unlike effect masks, a pre-mask input (the name of which is usually specific to each node using
them) is used by the node before the effect is applied. This usually causes the node to render
more quickly and to produce a more realistic result. In the case of the Highlight and the Glow
nodes, a pre-mask restricts the effect to certain areas of the image but allows the result of that
effect to extend beyond the limits of the mask.
The advantage to pre-masking is that the behavior of glows and highlights in the real world can
be more closely mimicked. For example, if an actor is filmed in front of a bright light, the light will
cause a glow in the camera lens. Because the glow happens in the lens, the luminance of the
actor will be affected even though the source of the glow is only from the light.
In the case of the DVE node, a pre-mask is used to apply a transformation to a selected portion
of the image, without affecting portions of the image outside of the mask. This is useful for
applying transformations to only a region of the image.
Garbage Matte Inputs
Garbage Matte inputs (usually colored gray) are used to exclude light stands, rigging, and boom
microphones that intrude upon masks being pulled via blue-screen and green-screen keys. In
the following example, a lighting stand to the left is removed from the image via a B-Spline
node’s mask connected to the Garbage Matte input of the DeltaKeyer node.
Chapter – 71 Rotoscoping with Masks 1441