MultiClean

MultiClean is a Python library for morphological cleaning of multiclass 2D numpy arrays (segmentation masks and classification rasters). It provides efficient tools for edge smoothing and small-island removal across multiple classes, then fills gaps using the nearest valid class.

Visual Example

Below: Land Use before/after cleaning (smoothed edges, small-island removal, nearest-class gap fill).

<img src="https://raw.githubusercontent.com/DPIRD-DMA/MultiClean/main/assets/land_use_before_after.png" alt="Land Use before/after" width="900"/>

Installation

pip install multiclean

or

uv add multiclean

Quick Start

import numpy as np
from multiclean import clean_array

# Create a sample classification array with classes 0, 1, 2, 3
array = np.random.randint(0, 4, (1000, 1000), dtype=np.int32)

# Clean with default parameters
cleaned = clean_array(array)

# Custom parameters
cleaned = clean_array(
    array,
    class_values=[0, 1, 2, 3],
    smooth_edge_size=2,     # kernel width, larger value increases smoothness
    min_island_size=100,    # remove components with area < 100
    connectivity=8,         # 4 or 8
    max_workers=4,
    fill_nan=False          # enable/disable the filling of nan values in input array
)

Use Cases

MultiClean is designed for cleaning segmentation outputs from:

• Remote sensing: Land cover classification, crop mapping
• Computer vision: Semantic segmentation post-processing
• Geospatial analysis: Raster classification cleaning
• Machine learning: Neural network output refinement

Key Features

• Multi-class processing: Clean all classes in one pass
• Edge smoothing: Morphological opening to reduce jagged boundaries
• Island removal: Remove small connected components per class
• Gap filling: Fill invalids via nearest valid class (distance transform)
• Fast: NumPy + OpenCV + SciPy with parallelism

How It Works

MultiClean uses morphological operations to clean classification arrays:

1. Edge smoothing (per class): Morphological opening with an elliptical kernel.
2. Island removal (per class): Find connected components (OpenCV) and mark components with area < min_island_size as invalid.
3. Gap filling: Compute a distance transform to copy the nearest valid class into invalid pixels.

Classes are processed together and the result maintains a valid label at every pixel.

API Reference

clean_array

from multiclean import clean_array

out = clean_array(
    array: np.ndarray,
    class_values: int | list[int] | None = None,
    smooth_edge_size: int = 2,
    min_island_size: int = 100,
    connectivity: int = 4,
    max_workers: int | None = None,
    fill_nan: bool = False
)

• array: 2D numpy array of class labels (int or float). For float arrays, NaN is treated as nodata and will remain NaN unless fill_nan is set to True.
• class_values: Classes to consider. If None, inferred from array (ignores NaN for floats). An int restricts cleaning to a single class.
• smooth_edge_size: Kernel size (pixels) for morphological opening. Use 0 to disable.
• min_island_size: Remove components with area strictly < min_island_size. Use 1 to keep single pixels.
• connectivity: Pixel connectivity for components, 4 or 8.
• max_workers: Parallelism for per-class operations (None lets the executor choose).
• fill_nan: If True will fill NAN values from input array with nearest valid value.

Returns a numpy array matching the input shape. Integer inputs return integer outputs. Float arrays with NaN are supported and can be filled or remain as NAN.

Examples

Cleaning Land Cover Data

from multiclean import clean_array
import rasterio

# Read land cover classification
with rasterio.open('landcover.tif') as src:
    landcover = src.read(1)

# Clean with appropriate parameters for satellite data
cleaned = clean_array(
    landcover,
    class_values=[0, 1, 2, 3, 4],  # forest, water, urban, crop, other
    smooth_edge_size=1,
    min_island_size=25,
    connectivity=8,
    fill_nan=False
)

Cleaning Neural Network Segmentation Output

from multiclean import clean_array

# Model produces logits; convert to class predictions
np_pred = np_model_logits.argmax(axis=0)  # shape: (H, W)

# Clean the segmentation
cleaned = clean_array(
    np_pred,
    smooth_edge_size=2,
    min_island_size=100,
    connectivity=4,
)

Notebooks

See the notebooks folder for end-to-end examples:

• Land Use Example Notebook: land use classification cleaning
• Cloud Example Notebook: cloud/shadow classification cleaning

Try in Colab

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.