Get the Bounding Box of a Mask#

The bounding box is the smallest axis-aligned rectangle containing all foreground pixels.

Basic usage#

bbox = mask.bbox()  # Returns [x, y, width, height]

The format matches COCO’s bounding box convention.

x, y, w, h = mask.bbox()

# Top-left corner
top_left = (x, y)

# Bottom-right corner (exclusive)
bottom_right = (x + w, y + h)

If the mask has no foreground pixels, bbox() returns [0, 0, 0, 0].

Check first if needed:

if mask.area() > 0:
    bbox = mask.bbox()
else:
    # Handle empty mask

To extract just the region containing the mask and get both the cropped mask and the box coordinates:

cropped, bbox = mask.tight_crop()

With COCO-format dicts:

import rlemasklib

bbox = rlemasklib.toBbox(mask_dict)  # Single mask
bboxes = rlemasklib.toBbox([mask1, mask2, mask3])  # Multiple masks