Compositing question - colored alpha

[markus_s_cg]

Hi all,

I have a compositing question. If I render my image with a V-ray shadow catcher and sun/sky I get a colored alpha. I understand that I have to save the alpha as a separate exr with the VFB output, since using RGBA only produces a mono channel alpha. I haven't figured out how to composite this in Photoshop so I get the same result as I get when I display the render in the VFB with a background turned on (see attached screenshot). I tried to open both passes with alpha applied in Photoshop, then I used divide since that was the only blend mode that looked close, but I get artifacts and the colors is not the same. I could try to use AE, but if anyone has any info on what the right workflow is I would really like it if someone points me in the right direction!

Does anybody know any good tutorials for this? If not maybe it's a good idea for the Chaosgroup team to make something one day?

[kosso_olli]

Photoshop doesn't understand colored alpha, which is a shame. What I do to preserve the color of the alpha, is render it with a shadow catcher on a white background. Then use the RGB channel of the render and put it in Photoshop.

[markus_s_cg]

Hi Oliver, I'm not sure I understand exactly your workflow. What do you do with it when you get it into Photoshop, and how do you composite this layer with the background?

Anyways, I would be interested in finding out how I can get the same results as the VFB composite in an external compositing software. Can Adobe AE or PS do this or do I need something like Nuke or Fusion? Does anyone know what the "right" way is, with linear workflow? If not, is there a way to save the precomposed output from VFB?