Graphics Reference
In-Depth Information
Figure 9-71
Node setup with a colored background and an AlphaOver node
Premultiplication
Premultiplicationcontrolstheorderinginwhichmultipleoverlaidalphavaluesarecalculated.Premultiplication
values that are incorrectly set can cause unwanted artifacts or halo effects. In this example, there are problems
withtheunconvertedpremultiplicationvaluesthatresultinsomeartifactsonthecoloredbackgroundandaround
the edge of the figure. These are fixed by the use of the Convert Premul option. You can see the difference
between the two rendered outputs in
Figure 9-72
(reproduced in the color insert of the topic).
