Layering up cgi passes in photoshop compositing

[12robot1983]

I thought id post this here as its more likely to have some hits from after effects users than photoshop, and i believe the same techniques will apply. 

I'm curious to know how to layer up various render passes to build the beauty pass in photoshop? I've seen some instances of maybe 5 passes, the base one being a GI, then lighting, reflect, specular, refract all on linear dodge mode and this replicate a beauty pass. However sometimes those passes are named differently, or there are many more and they dont blend in the same way. Also sometimes they're exr, layered psd, png...

How would i learn how each is meant to blend, which mode to use? The internet seems to be scarce on information about cgi compositing in photoshop. Im too old to be an intern, how do i learn?!

Thanks

[Mylenium]

You spend time with your 3D renderer and understand how it works. There's no generalized formula. Each renderer treats this differently and even your five layer example is already wrong. GI is not a base pass. and your results would already be wrong/ useless. Base is Diffuse/ Ambient/ Albedo and then you put everything else on top. Shadows and Ambien Occlusion are typically multiplied, highlights and relections use Add/ Screen/ Overlay. Again, it's not a fixed rule, though and there are major differences across different renderers, including how they treat linear color spaces, PBR materials and all that good stuff. I'm afraid you can't realyl avoid being the intern and learn these things based on what files you get handed over. This is realyl something that can't be discussed without having to write a big fat book.

Mylenium

[ShiveringCactus]

A rule of thumb you could start with if the image primarily white (like an Ambient Occulsion pass), then to remove the white use Multiply, and if it's primarily black, (like a lighting pass), use Screen.  The blending modes in scame sections perform similar tasks.  You can cycle through them by holding SHIFT and tapping either - or =