Name
filt_tano - hyperbolic tangent homomorphic Fourier filter
Usage
output = filt_tano(image, freq, fall_off, value, pad)
Input
- image
- input image (can be either real or Fourier)
- freq
- pass-band frequency
- fall_off
- fall off of the filter
- value
- value of the filter at zero frequency
- 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) = 1.0-(1.0-value)**0.5{tanh[(pi(f+f_L)/(2af_L))]-tanh[(pi(f-f_L)/(2af_L))]}`
where `f_L` if the the stop-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.
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.