Links:
http://www.originlab.com/doc/Origin-Help/FFT-Filter-Algorithm
http://www.originlab.com/doc/Origin-Help/2DFFT-Filter-Algorithm
http://www.imagemet.com/WebHelp6/Default.htm#FourierAnalysis/Band_Filtering.htm
http://www.math.utah.edu/software/gsl/gsl-ref_228.html (GSL low pass filter)

Filter reference:
http://docs.scipy.org/doc/scipy/reference/signal.html
https://www.centerspace.net/butterworth-filter-csharp

Features:

• Ideal filter (low/high pass, band pass/reject)
• filter dock
• Butterworth filter order 1..10
• Chebyshev I+II filter order 1..10
• documentation