[Numpy-discussion] nd_image.affine_transform edge effects

Stefan van der Walt stefan@sun.ac...
Fri Mar 23 05:04:03 CDT 2007


On Thu, Mar 22, 2007 at 11:20:37PM -0700, Zachary Pincus wrote:
> The actual transform operators then use these coefficients to  
> (properly) compute pixel values at different locations. I just  
> assumed that the "pre-filtering" was broken (even on natural images  
> with smooth variations) because images pre-filtered with the spline  
> filter didn't look like traditional pre-filtered images ought.
> 
> IMO, ticket 213 should be closed as PEBCAK (I'll do that forthwith);  
> further I'm sorry to have caused Peter to be further bothered about  
> this non-issue.

The ticket is more concerned with the usability of ndimage.
Currently, the principle of least surprise is violated.  If you use
the default arguments of ndimage.rotate (except for axes, which should
still be fixed to be (1,0) by default) and rotate Lena by 30 degrees,
you get something with green splotches on (attached to the ticket).

IMO, we should either change the default parameters or update the
documentation before closing the ticket.

Cheers
Stéfan


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