Butterworth Highpass Filtering
High pass filtering is a popular image enhancement method. Due to
a number of artifacts with "ideal" high pass filtering, there have been
a number of "smooth" high pass filters devised. The Butterworth high
pass filter is among the most popular due to its simplicity.
The butter -h program implements high pass pass filtering
(sharpening). The -l switch specifies low pass filtering (smoothing).
Additional command line arguments allow the user to select
the desired filter shape and cut off frequency.
(see code)
Command Usage
butter [options] infile outfile
[-l] Lowpass filtering
[-h] Highpass filtering
[-L] Homomorphic lowpass filtering
[-H] Homomorphic highpass filtering
[-f #] Frequency with filter = 1/2
[-n #] Denominator exponent
[-b #] Filter boost (Homomorphic only)
Example
butter -h -f 20 input.im butter.im
disp input.im butter.im
