Hi Andrea, scipy.ndimage.zoom will do this nicely for magnification. (Just set the spline order to 0 to get nearest-neighbor interpolation; otherwise you can use higher orders for better smoothing.)
For decimation (zooming out) scipy.ndimage.zoom also works, but it's not as nice as a dedicated decimation filter that would average properly over the area that's being squeezed into a single output pixel. (You'd have to choose the spline order manually to approximate that.) I'm afraid I don't have enough signal-processing background to know how to write a proper general-purpose decimation filter -- basically, you convolve with whatever bandlimiting filter (e.g. a gaussian, or do it in the Fourier domain), then just do nearest-neighbor downsampling, but I'm never sure how to properly choose the filter parameters! Between this and ndimage.zoom for magnifying, one could get together a much better "rebin" function that in the edge cases of integer magnification/minification should work the same as the IDL one. But the participants in the old discussion you highlighted seemed unhappy with the time/space used for proper decimation, so I'm not sure what really would be best. Zach On Nov 11, 2011, at 1:41 AM, Andrea Zonca wrote: > hi, > I work in astrophysics where the most common programming language is > currently IDL. > A common request of people switching from IDL to python is the > implementation of the REBIN function, which either downsizes a 2d > array by averaging or increases its dimension by repeating its > elements. In both cases the new shape must be an integer factor of the > old shape. > > I believe it is a very handy function for quick smoothing of 2 dimensional > data. > > I found a discussion about this topic in the archives: > http://thread.gmane.org/gmane.comp.python.numeric.general/885/focus=894 > > Do you think it would be useful to add such function to numpy? > > I created a simple implementation to help in the discussion: > https://gist.github.com/1348792 > > thanks, > Andrea Zonca > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
