CompuServe Messages

>>I believe it increases the antialiasing, which I need as now the labels (as .gif) come out clipped. But _why_ the alpha channel does this, I don't know. Actually, I'd love to figure out the benifits of Alpha beyond the transparancy issue…<< Glad you asked. As you said, the alpha channel describes the transparency of each pixel. This is used for two purposes: 1) transparent images, such as with objects assigned transparent materials, 2) antialiasing. Of the two, the second is more subtle, but far more important because it lets you composite multiple images with accurate antialiasied edges regardless of the background. If you look at antialiasing in a non-alpha program — like AniPro (Unzag ink) — you'll see that it's accomplished by creating a ramp of pixels at the border of one color that ramps into the color of the background. (e.g., for a red ball, you get a 2-3 pixel edge that's a gradient from red thru dark red, to black). Problem is, if you move that ball to a white background, the dark red pixels show up as a jaggy mess against the now-white background. (You can see this in Video Post if you composite with Queue RGB instead of Alpha.) HOWEVER (we're almost through here), if your image carries an alpha channel, you antialias it by providing a ramp of _transparency_ at the edges of the images. Thus the pixels at the edge of the red ball remain red, but ramp from opaque to semi-transparent, to almost transparent. Thus, regardless of its background, the red ball is perfectly antialiased. (Note that the alpha channel is required primarily for compositing operations where you're combining various images and don't know what their backgrounds will be.) 3ds, of course, uses alpha for later compositing either in video, or in Video Post. Alpha is also extensively used by Altamira Composer, where you can combine multiple 32-bit images that "float" anywhere on the screen with perfect antialiased edges because of the alpha. You can also use 3ds to create alpha images for later composition in AC. (Whew! Musta felt like writing this morning. If there are any typos in this, we'll have to live with it.) – Jack