title: Why do we convert from RGB to HSV
body: <p>I have a image and i want to detect a blue rectange in it. My teacher told me that:</p>
  
  <ul>
  <li>convert it to HSV color model</li>
  <li>define a thresh hold to make it become a binary image with the color we want to detect</li>
  </ul>
  
  <p>So why do we do that ? why don't we direct thresh hold the rgb image ?
  thanks for answer
  <img src="https://i.stack.imgur.com/L6AmO.png" alt="enter image description here"></p>