title: Javascript Canvas edge detection
body: <p>I would like to achieve this kind of image processing effect in Canvas : </p>
  
  <p><a href="http://schibum.blogspot.fr/2013/03/webgl-image-processing.html" rel="noreferrer">WebGL image processing</a></p>
  
  <p>What i need is an edge detection algorithm or explanation to draw only black pixels or border element ( such as a face for example ) of the image that an user can submit.</p>
  
  <p>cheers</p>