[Numpy-discussion] nd_image.affine_transform edge effects

Stefan van der Walt stefan@sun.ac...
Wed Mar 28 10:14:59 CDT 2007


Hi,

I notice now that we've been having this discussion on the wrong list
-- oops!  We're nearly done, though.

On Mon, Mar 26, 2007 at 04:16:51AM -0400, James Turner wrote:
> For what it's worth, I'd agree with both of you that the numeric
> overflow should be documented if not fixed. It sounds like Stefan has
> figured out a solution for it though. If you make sense of the code in
> "ni_interpolation.c", Stefan, I'd be very interested in how to make it
> calculate one less value at the edges :-).

I fixed the overflow issue in SVN.  I'd appreciate it if you could
test and let me know whether everything works as expected.  The output
values are now simply clipped to the bounds of the numeric type,
i.e. UInt8 to [0,255] etc.

As for the values at the edges, I'm still working on it.

Since we have a fundamental problem with the spline filter approach at
the borders, we may also want to look at subdivision interpolation
schemes, like the one described in this article:

http://citeseer.ist.psu.edu/devilliers03dubucdeslauriers.html

Regards
Stéfan


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