[Gimp-developer] Tuning and choosing resampling methods in GEGL/GIMP

Evaluating many mildly diverging images is part of image development,
but as much as possible should not need to be part of the workflow for
operators of software like GIMP. Providing many toggles, options and
references is a way to botch complicate the user interface visually as
well burden the cognitive load of the operator with choices.

The code of the lohalo/nohalo samplers needed revisiting recently (due
to hangs/slowdowns which now are resolved) - and as part of that
process the choice of a crucial parameter LOHALO_OFFSET0 and
NOHALO_OFFSET0 in the respective algorithms deserved revisiting. Test
renders of siginificant downscaling producing moire for nearest
neighbour and bad values for this parameter can be seen at
http://pippin.gimp.org/tmp/samplertest/ the current default is 13;
higher values lead to slower processing - for marginally better

It is probably possible to introduce some level of automation that
increases this value as downscaling is made even more aggressive - but
values around the current default seem reasonable. Note that for some
input images that do not produce moire, results might seem sharper -
but there might be lurking surprises in mini-moire patterns and
jaggies, for anything but nearest neighbor resampling antialiasing
should be expected for scaling of images.

The actual reason for this email is that I think it might be overkill
to have both lohalo and nohalo available as choices, they are related
and powerful transformation ellipsis aware methods, maybe it is
sufficient to have one go-to high quality resampler instead of
expecting the user to make a choice between lohalo and nohalo on a
case by case or built up as general preference, and in which case I
believe of these two related methods, from Nicolas Robidoux &
collaborators, we'd be best off keeping the nohalo method - possibly
with an adaptive _OFFSET0 to speed resampling that is primarily


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