Apple Shake 4 - Manual (Page 699)

Chapter 24 Keying 699
This converts the image back to RGB space.
The key is greatly improved. In particular, the original blockiness around the edge is
gone. Unfortunately, you’re still missing any fine detail that you might otherwise have
had were the footage shot using a different format.
Note: Using this method when you use straight YUV files, you can bypass the RGB to
YUV conversion by turning off yuvDecode in the FileIn node. Apply the Blur, and then
use one ColorSpace node to convert the image to RGB space.
The next method will use a different image, one with more hair detail that takes a little
more effort to preserve.
Without blur on UV channels With blur on UV channels