Transparent or semi-transparent shader will produce a semi opaque alpha, if it was rendered with a Maya shader

The following image is a Blinn shader rendered with mental ray, you can see the semi-opaque alpha

However if you assign a dielectric material or a Glass mia_material, you will get an opaque alpha.

 

To correct that behavior you will need a mib_transparency node Adjust the shading network to the following
mib_transparency outValue to the Material shader in the SG node
mia_material outValue to mib_transparency input
The Transp value in the mib_transparency node requires RGB value for it to work properly
Attaching a ramp node to it will give you the ability to control the opaque value in the alpha channel

The Shading netwrok.

Note: after talking to a co-worker, he pointed out that the above image is “wrong” because the cylinder should be white in the alpha (the part that overlap the plane)
To correct this:
I used the same method as described before, this time I used the mib_continue rather than the mib_transparency.

The reason I kept the previous work flow, is one of my composting friends liked the idea of having that look, according to him “it gives me more control in composting”

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This entry was posted on Tuesday, May 1st, 2007 at 7:23 pm and is filed under Mental ray. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.