HOG Cell (9-Bin)

Problem

Build a simplified 9-bin HOG histogram over a whole gradient map.

For each pixel with gradients (gx, gy), let mag = sqrt(gx^2 + gy^2) and bin = int((degrees(atan2(gy, gx)) mod 180) // 20) mod 9, then accumulate mag into that bin. Return the 9 bin sums rounded to 4 decimal places.

Hint

Orientations live in [0, 180): 20 degrees per bin, folded with modulo.

Test cases

case 1

in: [[[1,0],[0,1]],[[0,1],[1,0]]]

expected: [2,0,0,0,2,0,0,0,0]

case 2

in: [[[0,0,0],[0,0,0],[0,0,0]],[[1,1,1],[1,1,1],[1,1,1]]]

expected: [0,0,0,0,9,0,0,0,0]

case 3

in: [[[3,0]],[[4,0]]]

expected: [0,0,5,0,0,0,0,0,0]

case 4

in: [[[1,1]],[[1,-1]]]

expected: [0,0,1.4142,0,0,0,1.4142,0,0]

Starter codePython

def hog_cell(gx, gy):
    # Your code here
    pass

4 test cases · run your code against them in the editor