These constants define the different kind of filter brands available.

Values:

IG_FREQIP_FILTER_BRAND_IDEAL	0	Ideal Filter.
IG_FREQIP_FILTER_BRAND_BUTTERWORTH	1	Butterworth Filter.
IG_FREQIP_FILTER_BRAND_GAUSSIAN	2	Gaussian Filter.
IG_FREQIP_FILTER_BRAND_CHEBYSHEV_I	3	Type 1 Chebyshev Filter.
IG_FREQIP_FILTER_BRAND_CHEBYSHEV_II	4	Type 2 Chebyshev Filter.