Graphics Reference
In-Depth Information
Figure 9-69
The intersection (product) of both mattes
Using Alpha Overlays and Premultiplication
Younowhaveanicegreenscreenmattewithasolidblackbackgroundandasolidwhiteforegroundintheshape
of the character. You can group the whole node setup by selecting all of the nodes between the input and output
nodes and pressing Ctrl+G. This matte will be used to set the alpha value of the foreground image so that the
white areas (the character) are fully opaque (alpha 1) and the background areas are fully transparent (alpha 0).
The way to do this is to use a Set Alpha node, which you can add by pressing Shift+A and choosing Converter
> Set Alpha from the Add menu, as shown in
Figure 9-70
. Connect the original image to the Image socket and
connect the matte to the Alpha socket.
