hysteresis.py

def hysteresis(img, weak, strong=255):
    M, N = img.shape  
    for i in range(1, M-1):
        for j in range(1, N-1):
            if (img[i,j] == weak):
                try:
                    if ((img[i+1, j-1] == strong) or (img[i+1, j] == strong) or (img[i+1, j+1] == strong)
                        or (img[i, j-1] == strong) or (img[i, j+1] == strong)
                        or (img[i-1, j-1] == strong) or (img[i-1, j] == strong) or (img[i-1, j+1] == strong)):
                        img[i, j] = strong
                    else:
                        img[i, j] = 0
                except IndexError as e:
                    pass
    return img

In canny algorithm: "This can be done by starting at the known edge pixels and moving in all eight directions recursively until the gradient magnitude is less than or equal to the low threshold". I don't see recursive here. Can you explain your code when you determine eight directions of current pixel without considering from "sure-edge" pixel ?

i think here is mistake, for each neigbours you must do this checking recursively