Dithered Output

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ben++at++vislab.su.edu.au
Mon, 6 Feb 95 12:30:13 +1100


DITHERED OUTPUT
---------------

Hi Performer people,

We're dumping our image frames from performer to an ACCOM
video disk, and have found that we get different results in
the image quality depending on whether we record the output
from our crimson vgx, vs. our indigoII extreme.

The Indigo2 extreme dithers its' output in a regular pattern
that causes terrible shimmer in the non-interlaced display
from the ACCOM. The crimson doesn't dither. The problem can be
seen if we show seperate still-fields from the accom: one field
seems brighter than the other, due to the regular dithering
pattern. If you run "/usr/demos/bin/snoop" (or xmag) in the
performer window you can see the dither pattern.

Our target system will use an Indigo2. The display quality must
be suitable for broadcast (PAL) tv. Is there a way to get
non-dithered output from an extreme graphics board? We have
reduced the colour range, but the shimmer remains because the
fields are different in brightness. Are we stuck with it?

Does performer always dither on an indigo2 extreme?

regards,
ben.

_______________________________________________________
Ben Simons Physics Building, A28,
VisLab Systems Manager Sydney University. NSW.
Phone +61-2-351-3005 AUSTRALIA. 2006.


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