title: tracking multiple objects by color OpenCV 2.x
body: <p>Currently i am trying to track multiple objects by color. I've based on documentation code.</p>
  
  <pre><code>import cv2
  import numpy as np
  
  cap = cv2.VideoCapture(0)
  
  while(1):
  
      # Take each frame
      _, frame = cap.read()
  
      # Convert BGR to HSV
      hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
  
      # define range of blue color in HSV
      lower_blue = np.array([110,50,50])
      upper_blue = np.array([130,255,255])
  
      # Threshold the HSV image to get only blue colors
      mask = cv2.inRange(hsv, lower_blue, upper_blue)
  
      # Bitwise-AND mask and original image
      res = cv2.bitwise_and(frame,frame, mask= mask)
  
      cv2.imshow('frame',frame)
      cv2.imshow('mask',mask)
      cv2.imshow('res',res)
      k = cv2.waitKey(5) &amp; 0xFF
      if k == 27:
          break
  
  cv2.destroyAllWindows()
  </code></pre>
  
  <p>With the above code I am tracking blue colored objects filtering the HSV blue channel. I want to simultaneously track Green colored objects and show both blue and Green in 'res' image.</p>
  
  <p>I've added the following code without success</p>
  
  <pre><code>lower_green = np.array([50, 100, 100])
  upper_green = np.array([70, 255, 255]) 
  green_mask = cv2.inRange(hsv, lower_green, upper_green) # I have the Green threshold image.
  </code></pre>
  
  <p>I don't know how to add Green mask and mask (blue) in only one 'res' image using <code>bitwise-and</code>. Could you provide me some guidance.</p>
  
  <p>Thanks in advance.</p>