Differences between revisions 10 and 11
 ⇤ ← Revision 10 as of 2010-07-02 18:34:47 → Size: 1482 Editor: 139 Comment: ← Revision 11 as of 2013-07-01 13:12:58 → ⇥ Size: 1483 Editor: localhost Comment: converted to 1.6 markup Deletions are marked like this. Additions are marked like this. Line 13: Line 13: . 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_units|absolute frequency units]] {{{`f_a`}}} and their valid range is [0:0.5].

Name

filt_tanh - hyperbolic tangent high-pass Fourier filter

Usage

output = filt_tanh(image, freq, fall_off, pad)

Input

image
input image (can be either real or Fourier)
freq
pass-band 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).

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) = 1.0-0.5{tanh[(pi(f+f_H))/(2af_H))]-tanh[(pi(f-f_H))/(2af_H))]}`

where `f_H` if the the pass-band frequency (freq) and a is the filter fall-off (fall_off).

Reference

Basokur, A. T., 1998. Digital filter design using the hyperbolic tangent functions. Journal of the Balkan Geophysical Society 1, 14-18.

Pawel A. Penczek

category 1
FILTER
category 2
FOURIER

filter.py

Maturity

stable
works for most people, has been tested; test cases/examples available.

Bugs

None. It is perfect.

filt_tanh (last edited 2013-07-01 13:12:58 by localhost)