Creating Gaussian filter of required length in python

Question

Could anyone suggest which library supports creation of a gaussian filter of required length and sigma?I basically need an equivalent function for the below matlab function:

fltr = fspecial('gaussian',[1 n],sd)

Answer 1

Try scipy.ndimage.gaussian_filter, but do you really want the kernel or do you also want to apply it? (In which case you can just use this function.) In the former case, apply the filter on an array which is 0 everywhere but with a 1 in the center. For the easier-to-write 1d case, this would be for example:

>>> ndimage.gaussian_filter1d(np.float_([0,0,0,0,1,0,0,0,0]), 1)
array([  1.33830625e-04,   4.43186162e-03,   5.39911274e-02,
         2.41971446e-01,   3.98943469e-01,   2.41971446e-01,
         5.39911274e-02,   4.43186162e-03,   1.33830625e-04])

Answer 2

You don't need a library for a simple 1D gaussian.

from math import pi, sqrt, exp

def gauss(n=11,sigma=1):
    r = range(-int(n/2),int(n/2)+1)
    return [1 / (sigma * sqrt(2*pi)) * exp(-float(x)**2/(2*sigma**2)) for x in r]

Note: This will always return an odd-length list centered around 0. I suppose there may be situations where you would want an even-length Gaussian with values for x = [..., -1.5, -0.5, 0.5, 1.5, ...], but in that case, you would need a slightly different formula and I'll leave that to you ;)

Output example with default values n = 11, sigma = 1:

>>> g = gauss()
1.48671951473e-06
0.000133830225765
0.00443184841194
0.0539909665132
0.241970724519
0.398942280401
0.241970724519
0.0539909665132
0.00443184841194
0.000133830225765
1.48671951473e-06

>>> sum(g)
0.99999999318053079