[Tutor] Masked arrays & scipy.ndimage.<filters>

[Steven D'Aprano]

Koen De Munter wrote:
> Dear tutors,
> 
> Given an image, I want to generate another image with the mean values of
>  the pixels in their neighbourhood, thereby ignoring some of the 
> neighbouring pixels (e.g. the padded boundary). I hoped I could use 
> masked arrays for that, but apparently, this does not work.

Define "does not work".

Do you get an exception? Your computer crashes? You get a result, but it's not 
the result you were expecting? Something else?



> --
> def fnc(buffer)
>      return numpy.mean(buffer)

> mean = scipy.ndimage.generic_filter(masked_array, fnc, footprint = f, mode = 'constant', cval = 0.0)


scipy, even more than numpy, is a fairly specialised library. You may have 
better luck asking this question on a dedicated scipy mailing list.

> Is there a way to get around this issue, or do I have to accept the filter function can not handle masked arrays?

What does the documentation for generic_filter say?

What happens if you test it with a really small, simple example, say an array 
of just five or six values? Can you show us what you expect to get and what 
you actually get?



-- 
Steven