This takes an image (<a href="//commons.wikimedia.org/wiki/File:Barns_grand_tetons.jpg" title="File:Barns grand tetons.jpg">Image:Barns grand tetons.jpg</a>) and displays the Y, Cb and Cr elements of it.
Note that the Y image is essentailly a greyscale copy of the main image; that the white snow is represented as a middle value in both Cb and Cr; that the brown barn is represented by strong Cb and strong Cr; that the green grass is represented by strong Cb and weak Cr; and that the blue sky is represented by weak Cb and weak Cr. The murkiness of the Cb and Cr elements (to the human eye) demonstrate why many image compression codecs downsample colour; details in Y are much more visible than in Cb or Cr.
<a href="//commons.wikimedia.org/wiki/User:Mike1024" title="User:Mike1024">Mike1024</a>
Based on the (public domain) photo <a href="//commons.wikimedia.org/wiki/File:Barns_grand_tetons.jpg" title="File:Barns grand tetons.jpg">Image:Barns grand tetons.jpg</a>. Code above and resulting output by Mike1024.