import cv2
import numpy as np
def cleanImageBackground(image_name, ksize, option=1):
  '''
  Ref: stackoverflow.com/../what-processing-steps-should-i-use-to-clean-photos-of
  -line-drawings
  '''
  img = cv2.imread(image_name)
  img_blur = cv2.blur(img, (8, 8))
  img_white = cv2.dilate(img_blur, np.ones((ksize, ksize), np.uint8))
  
  img_gray = cv2.imread(image_name, 0)
  ht, wd, ch = img.shape
  for y in range(0, ht):
    for x in range(0, wd):
      if(option == 1):
        img_gray[y, x] = min(255, 
        max(255 * int(img[y, x, 0]) / int(img_white[y, x, 0]),
        255 * int(img[y, x, 1]) / int(img_white[y, x, 1]), 
        255 * int(img[y, x, 2]) / int(img_white[y, x, 2]) ) )
      else:
        img_gray[y, x] = min(255, 
        max(255 + int(img[y, x, 0]) - int(img_white[y, x, 0]), 
        255 + int(img[y, x, 1]) - int(img_white[y, x, 1]), 
        255 + int(img[y, x, 2]) - int(img_white[y, x, 2]) ) )
  return img_gray

ret, img_thresh = cv2.threshold(cleanImageBackground('imgCleanBg.png', 15, 2), 
  0, 255, cv2.THRESH_BINARY+cv2.THRESH_OTSU)
cv2.imwrite('imgCleanedBg.png', img_thresh)