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GSoC 2009: implementing multiple quality levels in resamplers

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Any suggestions RE: the intelligent way of implementing samplers with
multiple quality levels?

(Note that Adam and Eric may be able to figure this out without your
or my guidance, but in the interest of faster progress I am asking
"planning" questions here.)

My question will make more sense if I explain things a bit:

The nohalo family of resamplers has "levels," which are most easily
understood as "quality levels."

Currently, an outdated nohalo level 1 is in the gegl library as
gegl/gegl/buffer/gegl-sampler-sharp.c. (It is correct, but it is much
slower than it has to be.)

Nohalo level 2 is near ready (for VIPS), and by the end of the Summer
we hope to have levels 3 and 4 implemented in GEGL.

Now, these could be associated with quality requests (say, if quality
< .25, use nohalo level 1, if quality < .5 use level 2, etc).

Note, for example, that the footprint (stencil) gets larger as the
quality increases (think of Lanczos methods, for example).

How would you like this to be set up? Are there examples we could
follow?

A related issue:

The upcoming snohalo (snohalo level 1 is ready in VIPS, no progress on
snohalo level 2) also has quality levels (analogous to the nohalo
quality levels). The key aspect is that snohalo has a blur parameter
which, when set to 0, reduces the method to the same level nohalo,
which runs considerably faster (because, among other things, it has a
much smaller footprint). Any suggestion on how to implement this in
GEGL so that a call to snohalo actually return nohalo when blur <= 0,
but the codes are kept separate? Or should we simply put the two
together with an if statement which steers internally things toward
nohalo when they should?

Thanks (for your patience),

Nicolas Robidoux
Universite Laurentienne






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