[Numpy-discussion] nd_image.affine_transform edge effects

James Turner jturner@gemini....
Thu Mar 22 22:13:19 CDT 2007


By the way, ringing at sharp edges is an intrinsic feature of higher-
order spline interpolation, right? I believe this kind of interpolant
is really intended for smooth (band-limited) data. I'm not sure why
the pre-filtering makes a difference though; I don't yet understand
well enough what the pre-filter actually does.

I'm not sure what people normally do in computer graphics, since I'm
working more with natural band-limited images, but in the case of
Stefan's "rotate_artifacts" example, wouldn't it be appropriate to
use the 1st- or 0th-order spline instead of the 2nd order? If your
real-life data are smooth enough, however, then in theory the
ringing with higher orders should go away.

Sorry if I'm stating the obvious and missing the real point! I just
wanted to make sure this hasn't been overlooked... Likewise, sorry I
didn't mention this before if it does turn out to be relevant. Let
me know if you want references to explain what I said above.

James.



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