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← Revision 11 as of 20130701 13:12:58 ⇥
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. All frequencies are in [:absolute_frequency_units:absolute frequency units] {{{`f_a`}}} and their valid range is [0:0.5].  . All frequencies are in [[absolute_frequency_unitsabsolute frequency units]] {{{`f_a`}}} and their valid range is [0:0.5]. 
Name
filt_tanh  hyperbolic tangent highpass Fourier filter
Usage
output = filt_tanh(image, freq, fall_off, pad)
Input
 image
 input image (can be either real or Fourier)
 freq
 passband frequency
 fall_off
 fall off of the filter
 pad
 logical flag specifying whether before filtering the image should be padded with zeroes in real space to twice the size (this helps avoiding aliasing artifacts). (Default pad = False).
All frequencies are in absolute frequency units `f_a` and their valid range is [0:0.5].
Output
 output
 filtered image. Output image is real when input image is real or Fourier when input image is Fourier
Method
Fourier transform of the input image is multiplied by a radially symmetric hyperbolic tangent filter:
`H(f) = 1.00.5{tanh[(pi(f+f_H))/(2af_H))]tanh[(pi(ff_H))/(2af_H))]}`
where `f_H` if the the passband frequency (freq) and a is the filter falloff (fall_off).
Reference
Basokur, A. T., 1998. Digital filter design using the hyperbolic tangent functions. Journal of the Balkan Geophysical Society 1, 1418.
Author / Maintainer
Pawel A. Penczek
Keywords
 category 1
 FILTER
 category 2
 FOURIER
Files
filter.py
Maturity
 stable
 works for most people, has been tested; test cases/examples available.
Bugs
None. It is perfect.