FILTREsvg

HTML

<svg xmlns="http://www.w3.org/2000/svg" width="0" height="0">
 <filter id="grayscale" color-interpolation-filters="sRGB">
  <feColorMatrix type="matrix"  values="0.3333 0.3333 0.3333 0 0.001 0.3333 0.3333 0.3333 0 0.001 0.3333 0.3333 0.3333 0 0.001 0 0 0 1 0.001"/>
 </filter>
</svg>
<canvas id="myCanvas" width="300" height="300"></canvas>

CSS

#myCanvas:hover {
		filter: url(#grayscale); /* Firefox */		
		-ms-filter: url(#grayscale); /* IE */
		-webkit-filter: url(#grayscale); /* Webkit */
		}

JavaScript

var canvas = document.getElementById('myCanvas');
      var context = canvas.getContext('2d');
      var imageObj = new Image();

      imageObj.onload = function() {
        context.drawImage(imageObj, 0,0);
      };
      imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';