I'm mapping a sign that I created in photoshop onto a plane. The image has an alpha which I placed in the opacity of the material. The alpha is cutting out the area I don't want to see which is great. But the plane object is still rendering a square shadow rather than the shadow of the shape of the image.
Now here's the odd part, when I place the plane object with the image mapped on to it in front of a block with standard materials it renders fine.
But when I place it in front of a block object with mental ray materials on it, I get the shadow of the actual plane object.
I've attached the file showing what I mean if anyone is able to check it out.
The alpha in your .zip file is corrupt so I can't look at the file as it is. Regardless of that, I haven't ran into any problems with simply using a B&W image in the cutout map of an A&D material (see attached file).
I think the only time you'd run into any issues is if you were using ambient occlusion which does not recognize cutout/alpha's like these.
As I mentioned previously, AOCC will create a problem with cutouts because it doesn't recognize the cutouts, it only "see's" the actual geometry. So to clear the dark area on your render simply turn off the AOCC option on the A&D material applied to the box on the left (I'm assuming you're using _J.T._'s original file).
If you don't want to turn off the AOCC, then there are other ways to attack a scenario like this..for example: UVW mapping/unwrapping the mesh & placing the sign/label directly on the mesh via a painted texture...but that's certainly more labor intensive than the cutout method.
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