I'm creating short anims which have transparency and exporting them as png image sequences. I'm finding two issues with the export though:
1) The first frame is always solid black (when it should be totally transparent)
2) The R,G,B channels of each image are multiplied by the transparancy. So for example if I want a shape that's 50% transparent and coloured red the png should be 255,0,0,127 (R,G,B,A). In fact what After Effects is creating is a shape that's 127,0,0,127 (R,G,B,A)
Does anyone know what this issue is and how to solve it?
You can select straight Alpha in the render settings. The issue with the first frame is unknown to me, but may be a bug.
You should not have any problem with PNG as you have no choice but to have the alpha to straight (it's on of the only codecs that doesn't support premultiplied). Do you have the same problem is you select tiff sequences (LZW compression if you don't have much free space).