Run-Length Encoded Mask Operations

This library is an extended and improved version of the COCO API's pycocotools.mask module (which was originally written by Piotr Dollár and Tsung-Yi Lin).

It offers the following additional features:

• Further set operations (complement, difference, symmetric difference) in RLE, without decoding
• Mask cropping in RLE (rlemasklib.crop), without decoding
• Direct creation of full and empty masks in RLE
• Decompression of COCO's compressed RLE format to integer run-lengths, and vice versa
• Extra compression (optional) using gzip on top of the LEB128-like encoding used by the COCO API (~40% reduction beyond the COCO compression)
• More streamlined API

List of functions

Encoding / decoding

• rle_mask = rlemasklib.encode(binary_mask): Encode a binary mask as RLE
• binary_mask = rlemasklib.decode(rle_mask): Decode an RLE mask to a binary mask

Compression / decompression

• rle_mask = rlemasklib.compress(rle_mask): Compress an RLE mask using LEB128 (and optionally gzip)
• rle_mask = rlemasklib.decompress(rle_mask): Decompress an RLE mask from LEB128 or gzip to an array of integers (run-lengths)

Set operations

• rle_mask = rlemasklib.empty(imshape): Create an empty RLE mask of given size

• rle_mask = rlemasklib.full(imshape): Create a full RLE mask of given size

• rle_mask = rlemasklib.intersection(rle_masks): Compute the intersection of multiple RLE masks.

• rle_mask = rlemasklib.union(rle_masks): Compute the union of multiple RLE masks.

• rle_mask = rlemasklib.complement(rle_mask): Compute the complement of an RLE mask.

• rle_mask = rlemasklib.difference(rle_mask1, rle_mask2): Compute the difference of two RLE masks.

• rle_mask = rlemasklib.symmetric_difference(rle_mask1, rle_mask2): Compute the symmetric difference of two RLE masks.

• area = rlemasklib.area(rle_mask): Compute the area of an RLE mask

• iou = rlemasklib.iou(rle_mask1, rle_mask2): Compute the intersection-over-union of two RLE masks.

Cropping

• rle_mask = rlemasklib.crop(rle_mask, bbox): Crop an RLE mask to a given bounding box, yielding a mask with smaller height and/or width.

Conversions

• [x_start, y_start, width, height] = rlemasklib.to_bbox(rle_mask): Convert an RLE mask to a bounding box.
• rle_mask = rlemasklib.from_bbox([x_start, y_start, width, height], imshape): Convert a bounding box to an RLE mask inside a given image size.
• rle_mask = rlemasklib.from_polygon(polygon, imshape): Convert a polygon to an RLE mask inside a given image size.