FFT Filter
Frequency-domain filtering of a line profile or 2D data field using a Butterworth transfer function. Connect a LINE for 1D filtering or a DATA_FIELD for 2D filtering; the output mirrors the input type. Equivalent to Gwyddion fft_filter_1d / fft_filter_2d.
Inputs
| Name |
Type |
Required |
Description |
| input |
LINE or DATA_FIELD |
Yes |
Input line or field to filter |
Outputs
| Name |
Type |
Description |
| filtered |
LINE or DATA_FIELD |
Filtered output matching the input type |
Controls
| Name |
Type |
Default |
Description |
| filter_type |
dropdown |
lowpass |
Filter mode: lowpass, highpass, bandpass, or notch (band-reject) |
| cutoff |
FLOAT |
0.1 |
Lower cutoff frequency as a fraction of Nyquist (0.001–1.0) |
| cutoff_high |
FLOAT |
0.4 |
Upper cutoff for bandpass/notch modes (0.001–1.0) |
| order |
INT |
2 |
Butterworth filter order; higher values give steeper roll-off (1–10) |
Limitations
- cutoff_high is only used for bandpass and notch modes.
- The filter is applied in the frequency domain via FFT; very short lines may show wrap-around artefacts.
