Matte Ink or Background Transparent

From:         David Calaprice 
Subject:      Re: Matte vs Bg Transparent (was RE: Simple graphics question)
To:           DIRECT-L@UAFSYSB.UARK.EDU

Yes, Cody had it backwards.  Background transparent is more memory-
efficient, since matte internally generates a mask on-the-fly and keeps
this
mask in memory.

Matte has historically been slightly faster than background transparent,
although I haven't confirmed that this is still the case in D7.  There may
also be a slight performance hit the first time a given cast member is
displayed using matte ink during a session due to generation of the
mask.  This mask is cached in memory along with the associated
bitmap until the bitmap is unloaded or the movie is closed.

dc / Macromedia Director Engineering

D. Plänitz