Extensions
Extension 1:  Use the image gradient
1.same
2.for each edge point I[x,y] in the image
–    compute unique (d, q) based on image gradient at (x,y)
»    H[d, q] += 1
3.same
4.same
What’s the running time measured in votes?
Extension 2
•give more votes for stronger edges
Extension 3
•change the sampling of (d, q) to give more/less resolution
Extension 4
•The same procedure can be used with circles, squares, or any other shape