Excellent explorations here Veritas!! If you don't mind, I'm gonna throw in a little shortcut or tip if you will.... If you aren't painting your clouds on black or are not using a tool like that mentioned above and want to get your clouds for billboards from images then here's a quick shortcut to the necessary alpha..... Take your cloud image into PS or PSP and adjust the threshold...here it's set at 155. Then add a gaussian blur of a 2.0 radius to the black and white image and save. In Vue, load the image, the alpha and clik the little inverse dot. Presto! This is a quick one from one of Mayang's cloud images. Of course, you need to adjust diffuse, ambient and luminous for whatever atmosphere you have. Anyway, just my 1.5 cents worth....again, great pioneering here!!