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FFT Filtering Utility
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Navigation: Utilities > FFT Filtering Utility |
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The FFT (Fast Fourier Transform) dialog can be used to separate short wavelength components from long wavelength components. It can also be used to separate components of a surface that lie in a specific direction. For example, the grooves resulting from plateau honing in a measurement of a cylinder bore.
In the top right corner of the dialog is the power spectrum image obtained from the surface. The low frequency components are displayed in the center of the image and the long wavelength components are displayed at the edges of the image. The 'Power Spectrum Zoom' slider can be used to zoom in on the lower frequencies in the center of the image to help distinguish these components. The logarithmic scale can also be used to help visualize the weaker components in the power spectrum.
Ideal Low Pass Filter
The filter cutoff can be changed by changing the value in the edit box or by dragging the circle rendered on the power spectrum image. The ideal low pass filter will create a filtered surface composed of the wavelengths longer than the filter cutoff.
Note how only the low frequency components end up in the filtered surface to the right.
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Ideal High Pass Filter
The ideal high pass filter will create a filtered surface composed of the wavelengths shorter than the filter cutoff.
Note how only the high frequency components end up in the filtered surface to the right.
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Manual Filtering
The manual filtering feature allows you to select the exact Fourier components to be attenuated by the FFT filter.
Define the polyregion on the power spectrum image that you would like to filter. After defining the region, click the 'Discard' button to set the Fourier components in that region to zero. Clicking the 'Clear All' button will remove all of the regions.
Note how the predominant Fourier components, the cross-hatch grooves in the plateau honed piston bore, have been removed from the filtered surface. |
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