Compositing black pixels to transparent So I've rendered an animation with Transparent checked but I must have missed to set the saving mode for the .png to RGBA from RGB which has resulted in a black background instead of a transparent.

Is there any way for me to check for black pixels in the compositing and make them transparent, or do I just simple have to rerender it again with the correct format?

Thanks!
After your last node in the scene compositor, try adding a Chroma Key node (find it under Matte, Chroma Key). Set the Key color to black and play around with the rest of the settings.