ialogfilter

ialogfilter
Laplacian of Gaussian filter.

Synopsis

g = ialogfilter( f, sigma )

Implemented in Python.

Input

f	Image. Gray-scale (uint8 or uint16) or binary image (logical). input image
sigma	Double. Non-negative integer. scaling factor

Output

g	Image. Accepts any image data type.

Description

Filters the image f by the Laplacian of Gaussian (LoG) filter with parameter sigma. This filter is also known as the Marr-Hildreth filter. Obs: to better efficiency, this implementation computes the filter in the frequency domain.

Examples

>>> import Numeric

>>> f = iaread('cameraman.pgm')

>>> iashow(f)

(256, 256) Min= 0 Max= 251 Mean=137.066 Std=87.20

>>> g07 = ialogfilter(f, 0.7)

>>> iashow(g07)

(256, 256) Min= -269.655036756 Max= 310.836484048 Mean=1.337 Std=32.34

>>> iashow(g07 > 0)

(256, 256) Min= 0 Max= 1 Mean=0.583 Std=0.49


f	g07


g07 > 0

>>> import Numeric

>>> g5 = ialogfilter(f, 5)

>>> iashow(g5)

(256, 256) Min= -171.646121233 Max= 231.568565924 Mean=0.000 Std=48.06

>>> iashow(g5 > 0)

(256, 256) Min= 0 Max= 1 Mean=0.512 Std=0.50

>>> g10 = ialogfilter(f, 10)

>>> iashow(g10)

(256, 256) Min= -222.174752597 Max= 160.392577479 Mean=0.000 Std=50.27

>>> iashow(g10 > 0)

(256, 256) Min= 0 Max= 1 Mean=0.517 Std=0.50


g5	g5 > 0


g10	g10 > 0

Source Code

def ialogfilter(f, sigma):
    from Numeric import shape, NewAxis, array
    from FFT import fft2d, inverse_fft2d
    if len(shape(f)) == 1: f = f[NewAxis,:]
    h = ialog(shape(f), map(int, array(shape(f))/2.), sigma)
    h = iaifftshift(h)
    H = fft2d(h)
    if not iaisdftsym(H):
       iaerror("error: log filter is not symetrical")
       return None
    G = fft2d(f) * H
    g = inverse_fft2d(G).real
    return g