[SciPy-User] 2d convolution
Nico Schlömer
nico.schloemer at gmail.com
Sat Mar 20 12:07:00 EDT 2010
Thanks for the hint!
I've now set "mode='full'" and extract the data myself by
CR = scipy.signal.fftconvolve( C, R, mode='full' )
from scipy.signal.signaltools import _centered
CR = _centered( CR , C.shape )
Cheers,
Nico
On Sat, Mar 20, 2010 at 1:49 PM, <josef.pktd at gmail.com> wrote:
> On Sat, Mar 20, 2010 at 7:51 AM, Nico Schlömer <nico.schloemer at gmail.com> wrote:
>> Hi,
>>
>> I'm trying to compute the the convolution if s 2D array, and I see
>> that there are several ways in SciPy to do that. As the original data
>> C and the kernel R are about the same size in my case, I'd profit from
>> an FFT-based implementation, which I see right now is given by
>>
>> scipy.signal.fftconvolve( C, R,
>> mode='same' )
>>
>> and also
>>
>> scipy.stsci.convolve.convolve2d( data=C, kernel=R,
>> mode='constant', cval=0.0,
>> fft=1 )
>>
>> The second method is much faster than the first, and as far as I can
>> see it would spit out the the same results.
>>
>> Now, when the kernel is actually larger than the data, the resulting
>> array would have the shape of the kernel. Is there any way to restrict
>> the computations to the size of the data? At first, I thought that was
>> what "mode='same'"" is for.
>> I tried cutting the extra data off of the resulting array, but I'm not
>> quite sure which is the part that I would like to get rid of.
>>
>> Any hints here?
>
> It's always good to take a look at the source
>
> fftconvolve
>
> elif mode == "same":
> if product(s1,axis=0) > product(s2,axis=0):
> osize = s1
> else:
> osize = s2
> return _centered(ret,osize)
> elif mode == "valid":
> return _centered(ret,abs(s2-s1)+1)
>
> from scipy.signal.signaltools import _centered
>
> and it should be possible to set osize to s1 = array(in1.shape) (C
> in your notation)
>
> scipy.stsci has been removed recently from scipy and will not be in
> the scipy 0.8 version
>
> (I didn't try myself whether it works)
>
> Josef
>
>>
>> Cheers,
>> Nico
>> _______________________________________________
>> SciPy-User mailing list
>> SciPy-User at scipy.org
>> http://mail.scipy.org/mailman/listinfo/scipy-user
>>
> _______________________________________________
> SciPy-User mailing list
> SciPy-User at scipy.org
> http://mail.scipy.org/mailman/listinfo/scipy-user
>
More information about the SciPy-User
mailing list