Date: Fri, 27 May 1994 13:28:00 +1000
From: imagine-relay@email.sp.paramax.com

>From my limited understanding of computer graphics: alpha channels are 
used to quickly approximate transparency.  For example, some hardware & 
software claim to support 32bit color; this amounts to 4,294,967,296 
colors - doesn't sound practical, huh?-.  Well it isn't!  Only the first 
24bits are used for actual representation (16,777,216 colors) with the 
extra 8bits (256 colors) used for transparency purposes (0 often being 
completely transparent and 255 being opaque).  Some display hardware can 
take advantage of an alpha channel, freeing up the software from having to 
do pixel-by-pixel calculations for transparency.  However, a more common 
use for alpha channels is for masking images (rub-throughs, etc.).  

-- this was mostly conjecture.


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