title: How to convert a RGB image to a two dimensional image in Matlab
body: <p>I have a RGB image called <code>imrgb</code>, the size of which is <code>320*512*3</code>.
  I want to know how to convert it to a two dimensional image?<br>
  I saw some colorful images, but they are still two dimensional instead
  of three dimensional. Can anyone tell me how to convert it to a 
  two-dimensional image but still looks colorful?</p>
  
  <p><img src="https://i.stack.imgur.com/stxKY.jpg" alt="enter image description here"></p>