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docs/nodes/Grain Distributions.md

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+# Grain Distributions
+
+Compute a histogram distribution of a grain property from a labeled mask. Supported properties: area, equivalent diameter, mean height, max height, volume, and boundary length. Equivalent to Gwyddion's grain_dist.c module.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input surface data |
+| mask | IMAGE | Yes | Binary mask defining grain regions |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| distribution | LINE_DATA | Histogram of the selected grain property |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| property | dropdown | area | Grain property to plot: area, equiv_diameter, mean_height, max_height, volume, boundary_length |
+| n_bins | INT | 30 | Number of histogram bins (5–200) |
+| min_size | INT | 10 | Minimum grain size in pixels to include (1–100000) |
+
+## Notes
+
+- Volume is computed relative to the mean height of the non-grain (background) region.
+- Boundary length is estimated by counting boundary pixels and multiplying by the pixel size.
+- For per-grain statistics (not histograms), use Grain Analysis instead.
+- For aggregate summary statistics, use Grain Summary.