title: Get a quanity of pixels with specific color at image. Python, opencv
body: <p>I have small image. <a href="https://i.stack.imgur.com/iH4rN.png" rel="nofollow noreferrer">enter image description here</a>
  b g r, not gray. </p>
  
  <pre><code>original = cv2.imread('im/auto5.png')
  print(original.shape)  # 27,30,3 
  print(original[13,29]) # [254 254 254]
  </code></pre>
  
  <p>As you can see, there is white pic (digit 14) in my image, mostly black. On the right corner (coordinates [13,29]) I get [254 254 254] - white color.</p>
  
  <p>I want to calculate number of pixels with that specific color. I need it to further comparing such images with different numbers inside. There are different backgrounds on these squares, and I consider exactly white color. </p>