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Mental ray alpha channel renders only one side

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Raymond Ormaza
Mental ray alpha channel renders only one side
on Apr 16, 2011 at 5:15:32 am

Hello. I'm trying to render out a railing for a lighthouse which has been modeled with polygons in maya 2011. The railing itself is not composed of polygons. My intention is to render it with a targa or png image that has an alpha that will cut out the railing for me. The problem is that mental ray successfully does it but only on one saide of the polygon face. Mental Ray fails to render the opposite side transparency and simply replaces it with white. I am including a picture showing the problem. If anyone has come across this issue I'd love to hear how it was resolved. I'd prefer not to have to polygon model the railing. Thank you



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Tibor Bernscherer
Re: Mental ray alpha channel renders only one side
on Apr 16, 2011 at 9:46:09 pm

I've just read somewhere that the final gather doesn't really like to work with alpha channels, I'd export two different passes (if that's the case), one with and the other without the rails, just make sure that final gather is turned off when you export the pass with the rail. I'm not sure, but worth a try

Good Luck


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Steve Sayer
Re: Mental ray alpha channel renders only one side
on Apr 21, 2011 at 3:38:04 pm

I'm surprised at this... you'd think MR would be a little smarter than that.

A quick fix is to dupe those polys, reverse the normals on the dupe, and set both to 'single sided'. Then you'll have one version facing inwards, and one facing outwards, and they won't both be visible at the same time.

Hope that helps,

-Steve


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