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18.15.1 The FFT Filters Dialog Box

  • 2Dfft filters.png
  • Menu Command: Analysis: Signal Processing: 2D FFT Filters
  • Window Type: Matrix containing image that has been converted to data (Image: Conversion: Convert to Data).
  • X-Function Script and GUI Examples: fft_filter2
Dialog Theme See Dialog Themes.
Recalculate

See Recalculating Analysis Results.

Input Matrix

Specify the input matrix. Images should be converted into matrix data before applying 2D FFT Filter analysis. See Specifying Your Input Data.

Filter Type

Specify the filter type.

  • Low Pass: Low-pass filters remove all frequencies above the specified cut-off frequency, while keeping other frequencies unaltered.
  • High Pass: High-pass filters remove all frequencies below the specified cut-off frequency, while keeping other frequencies unaltered.
  • Band Pass: Band-pass filters remove all frequencies that are below the lower cutoff frequency or above the upper cutoff frequency, while keeping other frequencies unaltered.
  • Band Block: Band-block filters remove all frequencies that fall between the lower cutoff frequency and the upper cutoff frequency, while keeping other frequencies unaltered.
  • Threshold: Threshold filters allow only frequency components whose amplitudes are between the lower threshold value and the upper threshold value to pass.
Window Type

Specify the window type for 2D FFT filters. When Filter Type is set to Threshold, Window Type will not be shown in the dialog.

  • Butterworth: 2D Butterworth filter window.
  • Ideal: 2D Ideal filter window.
  • Gaussian: 2D Gaussian filter window.
  • Blackman: 2D Blackman filter window.
Order The filter order is a positive integer, whose default value is 1. This option is available only when Window Type is set to Butterworth.
Truncate Window This option is available only when Window Type is set to Blackman. It is used to specify whether to do zero cutoff.
Specify Cutoff By

Specify a way to define the cutoff value. When Window Type is set to Blackman, Specify Cutoff By will not be shown.

  • Fourier Pixel: Define cutoff frequency by Fourier Pixel. This can be any positive number of double type.
  • Fraction: Define cutoff frequency by Fraction. The value should be between 0 and 0.5.
  • Wavelength: Define cutoff frequency by Wavelength. The cutoff value should be larger than 0.
  • Hertz: Define cutoff frequency by Hertz. The cutoff value must be larger than 0.
Cutoff Value

This option is available only when the Filter Type is either Low Pass or High Pass. It specifies the cutoff value.

Lower Cutoff Value

Only available when the Filter Type is Band Pass or Band Block. Specifies the lower cutoff value.

Upper Cutoff Value

Only available when the Filter Type is Band Pass or Band Block. Specifies the upper cutoff value.

Lower Threshold

Only available when the Filter Type is Threshold. Specifies the lower threshold value. The value should be between 0 and 1.

Upper Threshold

Only available when the Filter Type is Threshold. The value should be between 0 and 1, and must be greater than the Lower Threshold value.

Output Matrix

Specify the output matrix, after processing by 2D FFT Filters analysis. See Output Results.

For more details about each option in the controls of the 2D FFT Filters dialog, see Algorithm of 2D FFT Filters.

 

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