code: '''
  Author: your name
  Date: 2021-07-02 17:20:23
  LastEditTime: 2021-07-08 16:28:05
  LastEditors: Please set LastEditors
  Description: In User Settings Edit
  FilePath: /genetic-drawing/2.py
  '''
  #coding:utf-8
  import cv2 
  import math
  import numpy as np
   
   
  def dodgeNaive(image, mask):
      # determine the shape of the input image
      width, height = image.shape[:2]
   
      # prepare output argument with same size as image
      blend = np.zeros((width, height), np.uint8)
   
      for col in range(width):
          for row in range(height):
              # do for every pixel
              if mask[col, row] == 255:
                  # avoid division by zero
                  blend[col, row] = 255
              else:
                  # shift image pixel value by 8 bits
                  # divide by the inverse of the mask
                  tmp = (image[col, row] << 8) / (255 - mask)
                  # print('tmp={}'.format(tmp.shape))
                  # make sure resulting value stays within bounds
                  if tmp.any() > 255:
                      tmp = 255
                      blend[col, row] = tmp
   
      return blend
   
   
  def dodgeV2(image, mask):
      return cv2.divide(image, 255 - mask, scale=256)
   
   
  def burnV2(image, mask):
      return 255 - cv2.divide(255 - image, 255 - mask, scale=256)
   
   
  def rgb_to_sketch(src_image_name, dst_image_name):
      img_rgb = cv2.imread(src_image_name)
      img_gray = cv2.cvtColor(img_rgb, cv2.COLOR_BGR2GRAY)
      # 读取图片时直接转换操作
      # img_gray = cv2.imread('example.jpg', cv2.IMREAD_GRAYSCALE)
   
      img_gray_inv = 255 - img_gray
      img_blur = cv2.GaussianBlur(img_gray_inv, ksize=(21, 21),
                                  sigmaX=0, sigmaY=0)
      img_blend = dodgeV2(img_gray, img_blur)
   
      cv2.imshow('original', img_rgb)
      cv2.imshow('gray', img_gray)
      cv2.imshow('gray_inv', img_gray_inv)
      cv2.imshow('gray_blur', img_blur)
      cv2.imshow("pencil sketch", img_blend)
      cv2.waitKey(0)
      cv2.destroyAllWindows()
      cv2.imwrite(dst_image_name, img_blend)
   
   
  if __name__ == '__main__':
      src_image_name = '02.jpg'
      dst_image_name = 'sketch_02.jpg'
      rgb_to_sketch(src_image_name, dst_image_name)
  
apis: numpy.zeros