How to get Opacity Map functionality with mental ray Arch & Design Materials?

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  09 September 2013
Question How to get Opacity Map functionality with mental ray Arch & Design Materials?

EDIT: Right after posting this I found a book section that explained that cut-out *does* recreate opacity map functionality, and the reason I thought it wasn't is because the mapping of the absolute grayscale values of the map to transparency was different to the other app, making it appear the cut-out was just cutting out and doing nothing else.

If I change the Colour Map on the bitmap to map push the whole map into a slightly higher range, it works as expected.

Is this due to Max having a slightly different colour space to the system? Is there a 'correct' mapping to use in this case or do I have to do it 'by eye'?

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Hello,

I am creating a script that imports assets from another application, and as part of it, it creates mental ray Arch & Design materials. The original app used Opacity Maps though and I can't see how to recreate the behavior of these in mental ray.

Cut-Outs only work in a subset of cases.

At the moment I am using Translucency maps, by

* Setting Transparency to 0.5
* Turning on Translucency
* Turning on the Thin Walled option
* Setting the Translucency colour to the Diffuse colour
* Placing the Opacity Map in the Translucency Weight Map slot

This doesn't work where the Opacity Map has a multiplier any less than 1 though as none of the options such as Transparency or the Opacity Map Output Modifier change the overall transparency linearly with the map.

I think this is because Translucency and Transparency in mental ray are very different and the Weight Map is not a 'translucency value' but another 'ratio' (the influence of Translucency vs. Transparency), right?

In Maya there is an option to use 'traditional' opacity maps isn't there? Does anything like this exist in Max?

How do I use an 'Opacity Map' in Max?

SJ

Last edited by sebjf : 09 September 2013 at 11:54 AM.
 
  09 September 2013
Yes, Autodesk needs to have funny name for everything. They needed to rename mia_material to Arch&Desing, to imply that it is only useful for architectural and design work, while it is more of a main renderer material like VrayMTL is in case of Vray. Just to confuse users and point them down the wrong road.

And cut-out map is exactly the same thing... if you want users to struggle searching for opacity slot in material, you got to invent a shitty name for it first
 
  09 September 2013
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