Rank Filter
Apply a general rank-order (morphological) filter to a DATA_FIELD. Selects the k-th smallest value within a local window, encompassing erosion, dilation, median, and arbitrary percentile operations. Equivalent to Gwyddion's rank-filter.c module.
Inputs
| Name |
Type |
Required |
Description |
| field |
DATA_FIELD |
Yes |
Input field to filter |
Outputs
| Name |
Type |
Description |
| filtered |
DATA_FIELD |
Rank-filtered field |
Controls
| Name |
Type |
Default |
Description |
| radius |
INT |
3 |
Radius of the circular filter window in pixels (1–50) |
| operation |
dropdown |
median |
Filter operation: erosion (local minimum), dilation (local maximum), median (50th percentile), or percentile (custom rank) |
| percentile |
FLOAT |
50.0 |
Custom percentile rank, used only when operation is percentile (0.0–100.0) |
Notes
- Erosion (local min) shrinks bright features and expands dark ones. Dilation (local max) does the opposite.
- Median is equivalent to percentile = 50 and provides edge-preserving smoothing.
- The percentile parameter is ignored unless operation is set to percentile. A percentile of 0 is equivalent to erosion, and 100 is equivalent to dilation.
- The filter uses a circular (disc-shaped) kernel; the actual window diameter is 2*radius + 1 pixels.
- Combining erosion followed by dilation (opening) or dilation followed by erosion (closing) can be achieved by chaining two Rank Filter nodes.
