View Full Version : opacity maps not effecting alpha channel of render

02 February 2004, 05:19 PM

I've been searching and trying everything I know to solve this but there's still quite a bit I don't know about making materials work in mental ray...

I have a scene with some flags in it, And I have opacity maps on the flags to simulate tears and things...
The flags are on the horizon of my scene, so I need the sky and other things to show through that in my compositing program. Unfortunately, mental ray just renders the entire object in the alpha channel, and the opacity map doesn't show up at all...
The opacity does show up in the RGB channels so it looks okay in the image, but I obviously can't use the image for compositing....

In the meantime, I'm just re-rendering the scene's alpha channel with Maya Software renderer, but that takes quite a while and there must be a way to make mental ray do it...

I wouold appreciate any answers or links to help me...

Thanks for your time.:beer:

02 February 2004, 07:27 PM
It works for me at least. If your transparency Map is in an Alpha channel then just apply the texture file to the material and you'll be get the transparency connected too.

But if you use a separated file , connect the outTransparency from your file to the Transparency of the Material. It works fine.

02 February 2004, 12:01 AM

Software renderer does it fine, it's just mental ray.
Have I set anything up wrong? I don't know what else to say but it's definitely NOT working.

Thanks again.

02 February 2004, 07:16 PM
Weird ! It should works.
Look, try download this file, unzip then you find a maya scene with a 2 textures, on for color and the other for transpa. Try to render and tell me if it works cuz it's rendering fine with MR here.

The file

02 February 2004, 09:11 PM
aha...that scene worked fine.

I realized that it was the fact that I put a dome over the scene for an HDRI effect...and I had turned off the 'primary visibility' which worked just fine...but the dome continues to be visible through opacity maps and effect the alpha channel, too. Just in the spaces where the transparency maps are.

I tried changing all the settings I could think of on the HDRI dome and its image...I also looked to see if there was anything in the attributes for the transparency map....nothing is working.

So, the problem remains...Any ideas on why this would be happening, or a workaroud besides re-rendering the alpha channel in maya software?

02 February 2004, 03:33 PM
In your dome, go to the object level (not the shape node level where the Render Stats are, the tab to the left of that) and look at the "Flags" section under "Mental Ray." Uncheck the "derive from Maya" and set the Visible, Trace, and Shadow to "No", Caustic can be hidden, and set GI to "Cast Only." Then even if your number of refraction steps is too low, it should still stay out of the alphas.


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