png tight cut, cut the png background

png_tight_cut.py

import cv2
import os
import sys
import numpy as np


def tight_cut(path):
    path = os.path.abspath(path)
    file_name = os.path.basename(path)
    dir_name = os.path.dirname(path)
    img: np.ndarray = cv2.imread(path, cv2.IMREAD_UNCHANGED)
    alpha: np.ndarray = img[:, :, 3]
    x, y, w, h = cv2.boundingRect(alpha)
    mask = alpha.astype(np.bool)
    mask: np.ndarray = mask[..., np.newaxis]
    img[:, :, :-1] *= mask
    img[:, :, :-1] += (~mask).astype(img.dtype) * 255
    cv2.imwrite(os.path.join(dir_name, "cut_" + file_name), img[y:y + h, x:x + w])


def main():
    for path in sys.argv[1:]:
        tight_cut(path)


if __name__ == '__main__':
    main()