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[REBOL] Re: technology behind Morpheus ....

From: media:quazart at: 31-Oct-2001 10:27

----- Original Message ----- From: <[holger--rebol--com]>
> - REBOL uses what are refered to as "non-premultiplied transparency" > alpha values. The "transparency" indicates that the alpha channel > describes the amount of transparency, not opaqueness, so 0 means > solid and 255 means fully transparent. "non-premultiplied" means > that you can change alpha and color values independently, i.e. > the color information does not have to be adjusted when the alpha > value is changed.
being of the high-end (discreet flame-inferno / AVID DS / nothing real SHAKE) compositing trade, its nice to see that you seem to have gone in-depth with comping and alpha usage. This is one of the best description of the ages-old pre vs. un-premultiplied issue... you'd be surprised how many high-level artists don't completely understand this. And thanks for NOT using pre-multiplied compositing, which in the context of building UI's would REALLY have been a drag... by what I have read in the original mail I understand that images will be allowed to have varying levels of grey in their alpha channels or that it will be able to push one into the image at run-time... but I must ask one thing to be included as an effect word... a Matte Divide (MDiv) function... (or at least a doc with a description of the way do perform it with several effects operations in the effects tree). Cause without it, PRACTICALLY ALL 3d rendered images using mattes will be DESTROYED by comping. also note that if this subject isn't covered at least in part in the docs, you probably will get many support calls of the likes of: "why does my image have a dark-grey edge?"... nice work! and thanks for the in-depth update ... we'll all code with that information in mind (especially with the planned differences and won't use the specified undocumented "features" anymore)... -Max