The apertureSize parameter as described by the canny documentation does not give any difference in the detected edges.
Here is my code:
thresh1 = 100
thresh2 = 200
aperture1 = 3
aperture2 = 7
img = cv2.imread("lena.png", 0)
edges1 = cv2.Canny(img, thresh1, thresh2, aperture1)
edges2 = cv2.Canny(img, thresh1, thresh2, aperture2)
cv2.imshow("result aperture 3", edges1)
cv2.imshow("result aperture 7", edges2)
cv2.waitKey()
Why are both result images identical?