A matte is a grayscale image you use as either an alpha channel or a
mask to isolate certain parts of the image.
For example, if you wanted to crop an image inside a hexagon shape, you
would create a hexagonal matte and connect it to the node’s mask
Mattes can be simple (a shape or a gradient) or complex, based on the
colors in the image you want to use the matte on.
|Generate mattes || |
|Use a matte to isolate part of an image |
Connect the matte to a node’s mask input .
Connect the image to the first input of a Switch Alpha
node, and connect the matte to the
second input. The Switch Alpha operator copies the second
input to the alpha channel of the first input. Turn on the
Redo premultiply parameter to override any previous
Use the Premultiply operator to use a
matte stored in a plane of the image you want to isolate. Use
the name of the matte plane in the Alpha parameter.
Connect the image to the input of the node generating the
matte. In the Image tab of the matte node’s parameter
editor, change the Add image parameter to “C (RGB)” and
|Shrink or enlarge mattes |
Use the Expand or Dilate
Erode operator to shrink or enlarge mattes.
The Dilate Erode operator is faster, but does not provide good
quality for large changes. The Expand operator is slower, but
produces higher quality.
|Adjust edges and falloff of a matte |
Because mattes are just grayscale images, you can use the full
complement of image-manipulation tools in the compositor to
Use the Gamma operator to reduce falloff at
the low end (gamma < 1) or high end (gamma > 1).
Use an Expand operator with zero size and a
small Dropoff to add a bit of falloff to a map.
Use the Blur operator with a Gaussian blur to
soften a matte. You can also use the Edge Blur
operator, which blurs based on edge
detection and so may preserve fine details of the map better.
|Combine mattes || |