Setting individual pixels' Alpha Data for a plotted surface

Hi,

I've mapped an image to a plane in a 3D plot, using a 3D image array as my 'CData'. I now need to be able to control the individual pixels' alpha values in order to effectively control each pixel's transparency in the image. However, I've been having trouble getting the code to work, and after reading over the documentation and spending a while coding, I haven't figured it out.

I'd appreciate anyone's help.

Thanks, Rob