title: remove background of any image using opencv
body: <p>I have been searching for a technique to remove the background of a any given image. The idea is to detect a face and remove the background of the detected face. I have finished the face part. Now removing the background part still exists.</p>
  <p>I used this code.</p>
  <pre><code>import cv2
  import numpy as np
  
  #== Parameters           
  BLUR = 21
  CANNY_THRESH_1 = 10
  CANNY_THRESH_2 = 200
  MASK_DILATE_ITER = 10
  MASK_ERODE_ITER = 10
  MASK_COLOR = (0.0,0.0,1.0) # In BGR format
  
  
  #-- Read image
  img = cv2.imread('SYxmp.jpg')
  gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
  
  #-- Edge detection 
  edges = cv2.Canny(gray, CANNY_THRESH_1, CANNY_THRESH_2)
  edges = cv2.dilate(edges, None)
  edges = cv2.erode(edges, None)
  
  #-- Find contours in edges, sort by area 
  contour_info = []
  contours, _ = cv2.findContours(edges, cv2.RETR_LIST, cv2.CHAIN_APPROX_NONE)
  for c in contours:
      contour_info.append((
          c,
          cv2.isContourConvex(c),
          cv2.contourArea(c),
      ))
  contour_info = sorted(contour_info, key=lambda c: c[2], reverse=True)
  max_contour = contour_info[0]
  
  #-- Create empty mask, draw filled polygon on it corresponding to largest contour ----
  # Mask is black, polygon is white
  mask = np.zeros(edges.shape)
  cv2.fillConvexPoly(mask, max_contour[0], (255))
  
  #-- Smooth mask, then blur it
  mask = cv2.dilate(mask, None, iterations=MASK_DILATE_ITER)
  mask = cv2.erode(mask, None, iterations=MASK_ERODE_ITER)
  mask = cv2.GaussianBlur(mask, (BLUR, BLUR), 0)
  mask_stack = np.dstack([mask]*3)    # Create 3-channel alpha mask
  
  #-- Blend masked img into MASK_COLOR background
  mask_stack  = mask_stack.astype('float32') / 255.0         
  img         = img.astype('float32') / 255.0    
  masked = (mask_stack * img) + ((1-mask_stack) * MASK_COLOR)  
  masked = (masked * 255).astype('uint8')                    
  
  cv2.imshow('img', masked)                                   # Display
  cv2.waitKey()
  cv2.imwrite(&quot;WTF.jpg&quot;,masked)
  </code></pre>
  <p>But this code only works for only this image</p>
  <p><img src="https://i.stack.imgur.com/DcwkV.jpg" alt="" /></p>
  <p>What should be changed in the code to make it to work for different images</p>