#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import cv2
import numpy as np
import math 
"""
Created on Wed Jun 12 17:05:24 2019

@author: daniele
"""

def hog(img):
    gx = cv2.Sobel(img, cv2.CV_32F, 1, 0)
    gy = cv2.Sobel(img, cv2.CV_32F, 0, 1)
    mag, ang = cv2.cartToPolar(gx, gy)
    bin_n = 16 # Number of bins
    bin = np.int32(bin_n*ang/(2*np.pi))

    bin_cells = []
    mag_cells = []

    cellx = celly = 8

    for i in range(0,img.shape[0]/celly):
        for j in range(0,img.shape[1]/cellx):
            bin_cells.append(bin[i*celly : i*celly+celly, j*cellx : j*cellx+cellx])
            mag_cells.append(mag[i*celly : i*celly+celly, j*cellx : j*cellx+cellx])   

    hists = [np.bincount(b.ravel(), m.ravel(), bin_n) for b, m in zip(bin_cells, mag_cells)]
    hist = np.hstack(hists)

    # transform to Hellinger kernel
    eps = 1e-7
    hist /= hist.sum() + eps
    hist = np.sqrt(hist)
    hist /= math.norm(hist) + eps

    return hist