mask_to_coco_annotation.py

import json
import numpy as np
from pycocotools import mask
from skimage import measure

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

fortran_ground_truth_binary_mask = np.asfortranarray(ground_truth_binary_mask)
encoded_ground_truth = mask.encode(fortran_ground_truth_binary_mask)
ground_truth_area = mask.area(encoded_ground_truth)
ground_truth_bounding_box = mask.toBbox(encoded_ground_truth)
contours = measure.find_contours(ground_truth_binary_mask, 0.5)

annotation = {
        "segmentation": [],
        "area": ground_truth_area.tolist(),
        "iscrowd": 0,
        "image_id": 123,
        "bbox": ground_truth_bounding_box.tolist(),
        "category_id": 1,
        "id": 1
    }

for contour in contours:
    contour = np.flip(contour, axis=1)
    segmentation = contour.ravel().tolist()
    annotation["segmentation"].append(segmentation)
    
print(json.dumps(annotation, indent=4))