question

Matthew Goldblatt avatar image
Matthew Goldblatt asked ·

Reflection AOV, or alpha reflection/specular

So I can't figure out how, or if it's possible, to have a matte object that reflects with an alpha. Useful especially when your reflection is not additive, like comping an object and it's reflection onto a SHINY floor, where it's reflection is actually occluding light coming in the window.

I managed to turn on Indirect Specular in the shadow/matte map which gives me a correct reflection in my matte object, but the alpha is not solid, it's only a greyscale of the reflection colours.

One solution is to do a pass where the reflecting object is solid white, and then use this as the reflection alpha...but I'd rather set this up to work in one render pass (with whatever AOV's are necessary) instead of rendering twice.

any ideas?


BTW I'm using Max 2021 and arnold 6.1.0.0 and maxtoa 4.2.1.4

mattesshadow matte
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Matthew Goldblatt avatar image
Matthew Goldblatt answered ·

Sure! Please forgive me for the long post full of images.

Below is an example. Top: Beauty pass. Bottom: Shadow matte AOV using Arnold matte material on the plane.

beauty-shadowmatte.jpg


Next one

Top: Indirect Specular AOV, Arnold matte material with Shadowmatte map in colour input, Specular turned on. Below: alpha of that same AOV. (pure white)

indirect-spacular-aov.jpg

Next one

Top: Beauty pass with shadows turned off, and camera primary rays turned off for the cylinder

Below: resulting alpha. At least this gives me an alpha that means something. But as you can see, the alpha is really just a greyscale of the RBG render.

beauty-matte-material.jpg


Next one THIS IS WHAT I WANT

Top: reflection

Below: alpha of that reflection

This is not an actual render. For the below image, I gave the cylinder a flat white texture and rendered this out as a useable alpha.

desired-outcome.jpg

The object has a solid alpha so the reflection should as well. This would allow me to isolate the reflection. Wasn't a problem with Mental Ray.


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Ciro Cardoso avatar image
Ciro Cardoso answered ·

Can you share a screenshot of what you did in Max? Just to give an idea of what you are trying to do.

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