Focus and Depth of Field
13-Sep-94 15:56:49
Sb: #123573-Focus and Depth of Field
Fm: David Stinnett 70214,774
To: Alice [Wonderland] 74764,1443
Your explanation is exactly correct. The only reason you need
to split the alpha in this case is because BLUR ignores the alpha in
32 bit images. If you use BLUR to process a 32 bit image and
composite it later, the RGB portion of the image will be blurred, but
the alpha channel will stay sharp, which kinda ruins the effect. If
you split the alpha and run blur on it separately, then use it as an
RGB mask (not an alpha mask) in your composite, then it will work
fine. If you use something else to blur your frames that can process
all the channels in a 32 bit image, like photoshop, then you wouldn't
need to split the alpha.