Color Correction - Nuke 101: Professional Compositing and Visual Effects - page 175

13. Click Read1 and from the Merge toolbox add an Unpremult node.
14. Click Grade1 and from the Merge toolbox add a Premult node and look at the
Viewer ( FIGURE 4.26 ).
Figure 4.26. The proper premultiplication fixed the problem.
The problem has been fixed. This is one way to use proper premultiplication.
Let's look at another.
15. Select Unpremult1 and Premult1 and press the Delete key.
16. In Grade1's Properties panel, choose rgba.alpha from the (Un)premult By menu;
this automatically selects the associated check box ( FIGURE 4.27 ).
Figure 4.27. Using the (Un)premult By property does the same thing as the
Unpremult and Premult nodes workflow.