title: OpenCV error: Assertion failed (mask.size == src1.size) in binary_op
body: <p>I am trying to place a png image image of a hat over the head of a webcam 
  feed. </p>
  
  <pre><code>import cv2
  import numpy as np
  
  face_cascade = cv2.CascadeClassifier('haarcascades/haarcascade_frontalface_default.xml')
  
  # Load the overlay image: hat.png
  imghat = cv2.imread('hat2.png', -1)
  
  print imghat is None
  
  # Create the mask for the hat
  imghatGray = cv2.cvtColor(imghat, cv2.COLOR_BGR2GRAY)
  #cv2.imwrite("imghatGray.png", imghatGray)
  
  ret, orig_mask = cv2.threshold(imghatGray, 0, 255, cv2.THRESH_BINARY)
  #cv2.imwrite("orig_mask.png", orig_mask)
  
  # Create the inverted mask for the hat
  orig_mask_inv = cv2.bitwise_not(orig_mask)
  #cv2.imwrite("orig_mask_inv.png", orig_mask_inv)
  
  # Convert hat image to BGR
  # and save the original image size (used later when re-sizing the image)
  imghat = imghat[:,:,0:3]
  origHatHeight, origHatWidth = imghat.shape[:2]
  
  video_capture = cv2.VideoCapture(0)
  
  while True:
  
      ret, frame = video_capture.read()
  
      gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
      faces = face_cascade.detectMultiScale(gray, 1.3, 5, flags=cv2.cv.CV_HAAR_SCALE_IMAGE)
  
      for (x, y, w, h) in faces:
          print "x : %d , y : %d, w: %d, h: %d " %(x,y,w,h)
          cv2.rectangle(frame, (x,y), (x+w, y+h), (255,0,0), 2)
          #cv2.rectangle(frame, (x-15,y-h), (x+w+15, y), (255,255,0), 2)
  
          hatWidth = w
          hatHeight = hatWidth * origHatHeight / origHatWidth
  
              roi_gray = gray[y:y+h, x:x+w]
              roi_color = frame[y:y+h, x:x+w]
  
          # Center the hat
          x1 = x - 15
          y1 = y - h
          x2 = x1 + w + 30
          y2 = y1 + h
  
          #cv2.rectangle(frame, (x1,y1), (x2, y2), (0,255,0), 2)
  
          # Check for clipping
          if x1 &lt; 0:
              x1 = 0
          if y1 &lt; 0:
              y1 = 0
          if x2 &gt; 640:
              x2 = w
          if y2 &gt; 360:
              y2 = h
  
  
          print "x1: %d , y1 : %d, x2: %d, y2: %d " %(x1,y1,x2,y2)
          # Re-calculate the width and height of the hat image
          hatWidth = x2 - x1
          hatHeight = y2 - y1
  
          cv2.rectangle(frame, (x1,y1), (x2, y2), (255,255,0), 2)
          print "hatWidth: %d, hatHeight: %d" %(hatWidth, hatHeight)      
          # Re-size the original image and the masks to the hat sizes
          # calcualted above
          hat = cv2.resize(imghat, (hatWidth,hatHeight), interpolation = cv2.INTER_AREA)
          mask = cv2.resize(orig_mask, (hatWidth,hatHeight), interpolation = cv2.INTER_AREA)
          mask_inv = cv2.resize(orig_mask_inv, (hatWidth,hatHeight), interpolation = cv2.INTER_AREA)
  
          # take ROI for hat from background equal to size of hat image
          roi = roi_color[y1:y2, x1:x2]
  
          # roi_bg contains the original image only where the hat is not
          # in the region that is the size of the hat.
          roi_bg = cv2.bitwise_and(roi,roi,mask = mask_inv)
  
          # roi_fg contains the image of the hat only where the hat is
          roi_fg = cv2.bitwise_and(hat,hat,mask = mask)
  
          # join the roi_bg and roi_fg
          dst = cv2.add(roi_bg,roi_fg)
  
          # place the joined image, saved to dst back over the original image
          roi_color[y1:y2, x1:x2] = dst
  
          break
  
  
  
      # Display the resulting frame
          cv2.imshow('Video', frame)
  
  
          if cv2.waitKey(1) &amp; 0xFF == ord('q'):
              break
  
  # When everything is done, release the capture
  video_capture.release()
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>When I execute the program, the camera opens and closes abruptly. The error  shown is in the below line - </p>
  
  <p><strong>roi_bg = cv2.bitwise_and(roi, roi, mask = mask_inv)</strong></p>