Core Optical, Inc.
IsotropicBandPassFilter Constructor Industrial Strength, Scientific Grade
Instantiates a new IsotropicBandPassFilter with the specified properties.

Namespace: PrecisionImage.FrequencyDomainProcessing
Assembly: PrecisionImage (in PrecisionImage.dll) Version: 2.0.0.0 (2.0.0.0)
Syntax

public IsotropicBandPassFilter(
	float lowCutoff,
	float highCutoff,
	float lowFrequencyOrder,
	float highFrequencyOrder
)

Parameters

lowCutoff
Type: OnlineSystem Single
A OnlineSingle type that specifies the 50% attenuation of the pass-band rising edge.
highCutoff
Type: OnlineSystem Single
A OnlineSingle type that specifies the 50% attenuation of the pass-band falling edge.
lowFrequencyOrder
Type: OnlineSystem Single
A OnlineSingle that controls the slope of the pass-band rising edge (larger values induce steeper slope).
highFrequencyOrder
Type: OnlineSystem Single
A OnlineSingle that controls the slope of the pass-band falling edge (larger values induce steeper slope).
Exceptions

ExceptionCondition
OnlineSystem ArgumentOutOfRangeException Thrown when lowCutoff is less than or equal to 0.0, or greater than or equal to 1.0.
OnlineSystem ArgumentOutOfRangeException Thrown when highCutoff is less than or equal to 0.0 or gretaer than or eaula to 1.0.
OnlineSystem ArgumentException Thrown when lowCutoff is greater than or equal to highCutoff.
OnlineSystem ArgumentOutOfRangeException Thrown when lowFrequencyOrder is less than or equal to 0.0.
OnlineSystem ArgumentOutOfRangeException Thrown when highFrequencyOrder is less than or equal to 0.0.
Remarks

The IsotropicBandPassFilter is a Butterworth band-pass filter that allows for adjustment of the lower and upper frequency roll-off characteristics as well as the pass-band width. The filter is circularly symmetric and will suppress (or pass) all directional basis functions of a given frequency equally and based on the user-specified filter characteristics.

The pass-band characteristics of the filter are controlled by the four constructor arguments (or otherwise using the object's LowCutoff, HighCutoff, LowFrequencyOrder and HighFrequencyOrder properties if the object has already been instantiated). The lowCutoff and highCutoff arguments are the frequencies at which 50% attenuation occurs. The rate at which the attenuation changes in the frequency region about these points is controlled by the lowFrequencyOrder and highFrequencyOrder arguments. Note that the roll-off characteristics are a function of both the tuning parameters as well as the cutoff values.

The cutoff values are defined as Nyquist frequency-normalized values. To specify the lower frequency pass band rising edge to center at a frequency 25% of the maximum (Nyquist) sampling frequency, assign a value of 0.25f to lowCutoff. Likewise, to declare the pass-band upper frequency falling edge to center at 90% of the Nyquist frequency, assign 0.90f to highCutoff. Such a filter will therefore pass approximately 65% of the spectral content. The degree to which the pass band differs from the original spectrum will depend on the tuning parameters.

The lowFrequencyOrder and highFrequencyOrder parameters control the rising rate and falling rate of the pass band, respectively. Larger values will generate steeper rising/falling rates. A value of 5.0 - 10.0 will typically generate a gradual filter that induces less ringing than a value of 50.0 for example (which is virtually an ideal filter).

See Also