Re: rebin

At 9:14 AM -0400 2004-08-30, Perry Greenfield wrote:
> On Aug 27, 2004, at 8:34 PM, Russell E. Owen wrote:
>
> >  Any suggestions on an efficient means to bin a 2-d array?
> >  ...
> >  For example, to 2x2 bin a two-dimensional image, one would:
> >  average (0,0), (0,1), (1,0), (1,1) to form (0,0)
> >  average (0,2), (0,3), (1,2), (1,3) to form (0,1)
> >  ...
> Note that a boxcar smoothing costs no more than doing the above averaging.
> So in numarray, you could do the following:
>
> from numarray.convolve import boxcar
> b = boxcar(a, (n,n))
> rebinnedarray = b[::n,::n].copy()
>
> or something like this (I haven't tried to figure out the correct offset
> for the slice) where one wants to rebin by a factor of n in both dimensions.
> We should probably add a built in function to do this.

Thanks! Great suggestion!

I think the polished version (for nxm binning) is:

from numarray.convolve import boxcar
b = boxcar(a, (n,m), mode='constant', cval=0)
rebinnedarray = b[n//2::n,m//2::m].copy()

A rebin function would be handy since using boxcar is a bit tricky.

-- Russell


-------------------------------------------------------
This SF.Net email is sponsored by BEA Weblogic Workshop
FREE Java Enterprise J2EE developer tools!
Get your free copy of BEA WebLogic Workshop 8.1 today.
http://ads.osdn.com/?ad_id=5047&alloc_id=10808&op=click