compositing CGI light passes

[seb4d]

Hi,
i’m working on a 3D animation project and decided to make one pass per light, in order to composite them later with maximum flexibity. So in each pass I only activated 1 light.

Now in nuke I’m trying to combine theses passes to get my final diffuse pass. I use multiple merge nodes in Plus mode to blend one pass to another in a specific order.
Problem is I get a very ugly edge on my alpha borders. I tried premultiplying the read node first and same result.
Then I tried to use only one merge node and use multiple A inputs, problem solved.

Can anyone tell me how this works ? Why I get this problem when using multiple merge nodes ?

Thanks !

[sweryagf rrfr]

make sure you only use the RGB channels (not RGBA) in the merge node as it makes no sense to plus multiple alphas together

[yassine hanine]

Yes ! That’s it ! I Feel a bit stupid now as it was really obvious 🙂

Thank you very much for your help !

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