I have a problem with adding alpha for post-processing effects. Need to render up a .png sequence for a client. However, he is requesting that glares, halos and other post pro effects be included before he composites them in After Effects. The glares won’t show in the alpha of the images.
Try as I might, I cannot get it to work.
Is there some workaround that I’m missing? I really need this to work to please the client! I’m sorry for the lack of images, but my client wants the movie kept secret for now.
Just adding them as alpha will never get a good result… it’s just not the right maths to overlay them over other footage… which I guess is why blender doesn’t put them in the alpha channel…
if they’re lighting effects (flares) then they need to be output on black as a seperate pass then they can be combined in aftereffects using screen blend mode or additive…
one of many ways you might try is adding another render layer and use a material override for a matt black (no specular) material… or you could use matte layers but that’s more complex to describe…so read the wiki on that one!
if you’re using the glare node the above will not work…(it uses the luma of the image to decide where to glow… so the glare result will be different if the surfaces are replaced with matte black) luckily the glare node has a mix value slider…
the default 0 value gives you the glow composited over your footage… -1 gives you just the original footage, and +1 is just the glow… so you can output the pass and you get just the glow over black ready to combine in after effects as for flares above… in case that’s not quite clear, set mix to 1 in the glare node!
For just getting halos, have a renderlayer with no passes checked except “Halo.” Render it over black, and you have all the halo effects separated. It might also work for lens flares and so forth, but I doubt it works for the Glare node.