image_derivative_sobel.py

#!/usr/bin/env python3
# -*- coding: utf8 -*-
import sys, argparse
try:
    import cv2
    import numpy as np
    from scipy.ndimage import convolve
except ImportError:
    print("install opencv and scipy please", file=sys.stderr)
    sys.exit(1)

def main(img_path, y_direct=False):
    img = cv2.imread(img_path, cv2.IMREAD_GRAYSCALE).astype(np.float)
    kernel = np.array([[-1, 0, 1],
                       [-2, 0, 2],
                       [-1, 0, 1]])/8
    if y_direct:
        kernel = kernel.T
    deriv = convolve(img, kernel)
    return deriv

if __name__ == "__main__":
    import matplotlib.pyplot as plt
    parser = argparse.ArgumentParser()
    parser.add_argument("img_path", metavar="IMAGE_PATH", help="input image path")
    parser.add_argument("-y", "--y-direct",
                        dest="y_direct", action="store_true",
                        help="compute derivative along y axis")
    args = vars(parser.parse_args())
    deriv = main(**args)
    plt.imshow(np.abs(deriv), cmap='gray')
    plt.show()