def cell_hist(gradients):
h, w, d  = gradients.shape
window_size = 8
res_h = int(h / window_size)
res_w = int(w / window_size)
bins_number = 9
bin_width = (180 / bins_number)
bins = [bin_width * x for x in range(bins_number)]
result = np.zeros((res_h, res_w, bins_number))

for a in range(res_h):
    for b in range(res_w):
        fragment = gradients[a*window_size:(a+1)*window_size, b*window_size:(b+1)*window_size]
        hist = np.zeros(bins_number)

        for row in fragment:
            for pixel in row:
                nbin = int((pixel[1] // bin_width) % 9)
                hist[nbin] += ((pixel[1] - bins[nbin]) / bin_width) * pixel[0]
                if nbin != bins_number - 1:
                    hist[nbin+1] += ((bins[nbin+1] - pixel[1]) / bin_width) * pixel[0]
                else:
                    hist[0] += ((180 - pixel[1]) / bin_width) * pixel[0]
        result[a,b] = hist
return result