Hi guys, I seem to be having a silly little issue where I am compositing several videos over each other, and as I want them to be mixed based on their brightness I am using the add blend mode. However, this is making the compositions background black, when I need it to remain transparent.
I can only assume I'm doing something wrong or not aware of everything, but where the blended layer is black (ie the frame background) it shouldn't be doing anything at all to the back plate?
Many thanks for any help,
You are kinda contradicting yourself and I think fundamentally misunderstanding blending modes....
I want them to be mixed based on their brightness
Then "mix them based on brightness" using channel effects to derive an Alpha channel from lightness or luminance, not blending modes. You are mistaking the result of the blending operation as transparency, which it is not. All your pixels are stil there in terms of Alpha and fully opaque. At some point your comp background will simply show through, as it is the only part not considered in the blending operations, but all normal layers will accumulkate, forming hot white regions eventually and converseley eradicating other pixels.