ioumatch 0.1.1

Compute IoU matrices and one-to-one matching for segmentation evaluation

ioumatch

ioumatch is a lightweight Python library for evaluating instance segmentation masks.
It automatically computes the IoU matrix, performs a one-to-one matching between predicted and ground-truth objects (greedy or Hungarian), and outputs True Positives (TP), False Positives (FP), False Negatives (FN), and the F1-score.

It seamlessly handles:

• Binary masks (0/1 or 0/255), automatically converted into instance labels,
• Already-labeled masks (each object has its own integer ID),
• Image files (PNG, TIFF, etc.) or NumPy arrays directly.

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Installation

pip install ioumatch

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Core Features

Function	Description
evaluate_image(pred, gt)	Evaluate a single image (NumPy arrays)
evaluate_paths(pred_path, gt_path)	Evaluate two mask image files
evaluate_pairs(pred_glob, gt_glob)	Evaluate a batch of image pairs using glob patterns
to_instance_labels(mask)	Convert a binary mask into connected-component labels
iou_matrix_from_labels(pred, gt)	Compute the IoU matrix between prediction and GT
match_greedy / match_hungarian	One-to-one object matching algorithms

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Quick Example

import numpy as np
import ioumatch

# --- Example with NumPy arrays ---
pred = np.array([
    [0, 1, 1],
    [0, 0, 1],
    [0, 0, 0]
], dtype=np.uint8)

gt = np.array([
    [0, 1, 1],
    [0, 0, 0],
    [0, 0, 2]
], dtype=np.uint8)

res = ioumatch.evaluate_image(pred, gt, threshold=0.5)
print(res)
#  {'tp': 1, 'fp': 1, 'fn': 1, 'f1': 0.5, 'iou_matrix': array(...)}

# --- Example with files ---
res = ioumatch.evaluate_paths("pred_masks/img_01.png",
                              "gt_masks/img_01.png",
                              threshold=0.3)
print(res["f1"])

# --- Evaluate multiple pairs ---
agg, per_image = ioumatch.evaluate_pairs("pred_masks/*.png", "gt_masks/*.png", threshold=0.5)
print("Global F1:", agg["f1"])

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Key Parameters

Parameter	Type	Default	Description
threshold	float	0.5	Minimum IoU to consider a valid match
method	str	"greedy"	"greedy" = simple matching, "hungarian" = optimal if SciPy is installed
inclusive	bool	False	If True, accepts IoU values equal to the threshold
normalize	bool	True	If True, automatically converts binary masks to instance-labeled masks

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How It Works

1. Input normalization
   Binary masks (0/1 or 0/255) are converted to instance-labeled masks using connected components.

2. IoU matrix computation
   An IoU value is computed for each pair (predicted_object, ground_truth_object).

3. One-to-one matching

   • Greedy mode: iteratively picks the highest IoU and removes the corresponding row and column.
   • Hungarian mode: uses optimal global assignment (via scipy.optimize.linear_sum_assignment).

4. Metric computation

   • TP – matched pairs
   • FP – predictions with no corresponding GT
   • FN – GT objects not detected
   • F1 – harmonic mean:

     F1 = 2 * TP / (2 * TP + FP + FN)
     

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Example Visualization

import matplotlib.pyplot as plt
from ioumatch import iou_matrix_from_labels, to_instance_labels

pred = to_instance_labels(pred)
gt = to_instance_labels(gt)
M = iou_matrix_from_labels(pred, gt)

plt.imshow(M, cmap='hot', interpolation='nearest')
plt.title("IoU Matrix: Predictions vs Ground Truth")
plt.xlabel("Ground Truth objects")
plt.ylabel("Predicted objects")
plt.colorbar()
plt.show()

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API Summary

Module	Content
ioumatch.iou	Builds IoU matrices between labeled masks
ioumatch.matching	Matching algorithms (greedy and Hungarian)
ioumatch.metrics	Computes TP, FP, FN, F1, and handles image/batch evaluation
ioumatch.utils	Image I/O and binary→label conversions

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Dependencies

Required

• numpy

Recommended

• opencv-python – for connected components in binary masks
• matplotlib – for IoU matrix visualization
• scipy – for the Hungarian optimal matching

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Example Output

When evaluating one image pair:

TP = 2
FP = 1
FN = 1
F1 = 0.6667

And the IoU matrix might look like this:

[[0.9, 0.0],
 [0.2, 0.7]]

Where:

• Row = predicted objects
• Column = ground truth objects

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License

MIT License © 2025
You’re free to use, modify, and distribute ioumatch.
If you use it in research or a public project, a short mention is appreciated.

ioumatch - a simple, clean way to evaluate segmentation models without writing another 200-line script.