Matt Austern wrote:

Ken Weitzel writes:


Matt Austern wrote:


Chris Cox writes:


I've tried. Their engineer insists that it's 30x faster to work with
15 bit quantities than 16 bit ones.

Which is correct (for 0..32768 representation versus 0..65535
representation).

Perhaps this is offtopic, and perhaps you can't answer it without
revealing proprietary information, but can you explain why 15-bit
computation should be so much faster than 16-bit? (If there's a
publication somewhere you could point me to, that would be great.)
I've thought about this for a few minutes, I haven't been able to
think of an obvious reason, and now I'm curious.
Feel free to email me if you think this wouldn't be interesting to
anyone else.


Hi Matt...

Nor can I see even the slightest difference. None at all.

So - I suspect that we're looking at it from the wrong
end. Suspect it's the a/d converter that could be the
bottleneck?


Nope. If Chris says 16-bit image processing in Photoshop would be much
slower than 15, I have no doubt that he's right. I just don't know
why. I can easily believe there's some subtle algorithmic issue that
I haven't thought of. For that matter, I can easily believe there's
some glaringly obvious algorithmic issue I haven't thought of. I'm
just curious what it might be.

Hi...

Perhaps you're right... throw a little more fuel on
the fire for whatever enlightenment it may be worth.

When I first got my ati aiw card, I read the manual(s).

They claimed that they were going to do 32 bit color...
sort of. They explained that they were going to do
3 x 10, but not "waste" the remaining 2 bits; they were
using them for additional green levels.

I'll see if I can't somehow find those manuals,
and share the detail if/when I do.

Ken