> If you want to take matters into your own hands, you can do the scale
> yourself by calling the two unidimensional shear bottleneck functions
> to do the resampling. This would allow you to do things like always do
> the horizontal pass first.
Which would work out just fine. Sounds like I can count on horizontal-first
always being faster (maybe even under Tiger) since my v/h ratio never seems
to be greater than about 11/8.5 for some reason or other ;-) All my scaling
goes through 1 function and it shouldn't be a big deal to change it to shear
in 2 passes.
Explains a lot:
- I didn't notice it right away when I started upgrading from my old
home-grown (pre OSX, pre QuickTime 6) scaling algorithm: the first part of
the software I switched over is dealing with faxed images that usually come
in at 200hx100v dpi resolution, so horizontal dimension is larger. I had
thought it was just that fewer pixels overall meant the effect went
unnoticed, but the asymmetrical sampling caused the effect to not be there
at all.
- my tests with full-color images didn't raise a red flag--those images were
landscape.
> It may be we should reexamine that decision.
Possibly. As we move to larger monitors and higher resolution scans the
performance deteriorates pretty badly.
And now I remember 1 question I forgot earlier: it seems that vImage doesn't
tile these big images on a dual-processor machine. Not a big concern to me
since the client is not buying dual-processor machines, but just a
suggestion. At some point it becomes a definite performance win. Maybe a
feature request for Tiger...
FYI my ultimate goal is to be able to read, decompress, scale & display a
full-page (~850x1100) 2550x3300 (1-bit) scan in ~80ms. That's what's needed
to provide really good usability for "paperless office" type applications. I
don't think it can be done on current hardware, but I hope we can get there
in the next couple of iterations. And it would be a bonus if Apple gets
there before Wintel...
--
Scott Ribe
email@hidden
http://www.killerbytes.com/
(303) 665-7007 voice
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