This is about using some BCC filters, specifically the light filters like Glint, in AE on objects, text etc. with alpha channels. When applied to a raw or precomposed layer the whole background goes black.
Last April we had this little discussion, but I'm sad to say it was abandoned rather than solved.
Peter's recommendation of precomposing and using the original precomp as the background layer does not work on my machines. Playing around with the DREADFUL pixel chooser is like looking for a lost dog in a thunderstorm, at night. Some of it starts to work, but it's so touch and go, what a horrible invention. Other filters like Trapcode's Starglow just work. Except I don't like that filter.
So my question is, how do I get these filters to work with an alpha channel?
There is a pop-up toward the bottom of the BCC Glint filter that is labeled "Glint Background", which needs to be set to the background against which you would like to composite. Set the background layer in the pop-up and you should see the glints appearing on the foreground element with alpha over the background element. The Glint Preserve Alpha parameter just below this pop-up is there to control the amount of glint that spills over the alpha and onto the background element in the composite, with a setting of zero clipping the glint result to within the alpha confines and setting of 100 allowing the glints to completely spill over onto the background unclipped.
I hope this helps - please let me know if it work for you.