My test: I have tried to use the Blur plugin (with "Alpha determines radius") with a mask and with Blue Banana. The result is always the same activating or deactivating this option. I tried with the Alpha plugin and I found a (useless?) difference: with radius =0 it is the same between active and inactive option (image 1); with radius > 0, with active option the blur acts normally on the image but the Alpha plugin is completely deactivated (image 2). If the option is deactivated, the Alpha plugin continues to work and the Blur acts normally (image 3). In the CinCV manual you can't find this parameter: either it's original to CinHV or it's new to CinGG. I tried to look at the source code in Blur.C, finding references to "config.a_key" as opposed to just "config.a"; but I can't figure out how and when it intervenes.
