Sobel / Prewitt Edge Detection

[James Turner]

Hi Stefan & Chris,

I hope this isn't too OT, but it's interesting that people would
rather re-implement bits of ndimage than try to improve it. Maybe
it's just too much work for a small part of the functionality.
Can/should the scikit be viewed as a possible ndimage replacement in
the longer run? Ndimage is a bit of a worry for me, since we need
the type of functionality it provides but I'm not optimistic about
having resources to help maintain its code in the near future.

Just curious.

Thanks!

James.


On 19/04/11 12:45, Chris Colbert wrote:
> Goodluck making something faster than ndimage without considerable effort (I've
> already tried in Cython and was 10x slower). I read the ndimage source and it
> goes to great lengths to make optimum use of the cpu cache by allocating line
> buffers etc...
>
> What we need is to find a fast open source routine, wrap it with Cython, and
> package it with the scikit. I wouldn't suggest using the one from OpenCV unless
> we are desperate because it's implemented as a c++ filtering engine. However,
> they are using sse2 intrinsics and it's fast! Like 10x+ faster than ndimage.
>
>
> 2011/4/19 St�fan van der Walt <stefan at sun.ac.za <mailto:stefan at sun.ac.za>>
>
>     2011/4/19 St�fan van der Walt <stefan at sun.ac.za <mailto:stefan at sun.ac.za>>:
>      > Apparently, neither of these routines like integer images as inputs
>      > (should be mentioned in the docs). Here's the output for float
>      > images:
>
>     To be more specific, scipy.ndimage.convolve does not upcast
>     appropriately when convolving integer arrays with floating point
>     arrays. This alone seems like a good enough reason to have our own
>     version, although I agree that we should use the 1D separated filters.
>
>     It doesn't look as if there is an easy way to coerce numpy.convolve to
>     do the job, so I guess I should write something in Cython?
>
>     Regards
>     St�fan