Dennis Pierce (dpierce++at++digital.net)
Tue, 08 Oct 1996 00:48:34 -0400
I've seen a seemingly straight-forward question take at least
one fork, so here's an attempt to rejoin the paths.
1. The default number of bits per texel used on the RE and IMPACT are
DIFFERENT. This is not only based on the amount of TRAM installed,
either none, 1 MB or 4 MB, but also on just what has been "selected"
as the default by whoever wrote what demo you're viewing. In
the "Performer Town" demo refered to initially, the fewer number
of bits allocated to each chromatic band in the RGB texel does
lend itself to "banding" in the textured road. 16-bits for RE
vs. 12-bits for IMPACT means that 5-bits R is now compressed to
one-half the visual range, namely 4-bits. Similarly for G and B.
2. Ever since the PI, SGI's desktop machines (of which the IMPACT
is one) have used 12-bit frame buffers. Deskside and rack machines
have used 24-bit frame buffers. The 12-bit frame buffer leads to
what some have correctly called dithering. Remember "virtual 24"?
That was the original purple Indigo slogan and still lives. O2
does not follow this trend, but remember one RM6 has 160 MB of
frame buffer RAM, so you may approach the 1 GB main memory limit
by the time you configure a great color space, throw in the OS,
and tuck in your app. :^)
So, there are two issues which are distinct but seem to be becoming
blurred in this thread.
Hope this helps and good luck to all!
bye.
--
Dennis Pierce
POB 321206 CCB FL 32932
407.783.7656
dpierce++at++digial.net
http://www.digital.net/~dpierce
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