title: canvas2d toDataURL() different output on different browser
body: <p>I have the same image and the same size of canvas, but the output is different. I want the same output, how should I do it?</p>
  
  <pre><code>var canvas = document.createElement('canvas'),
      ctx = canvas.getContext('2d'),
      img = new Image;
  
  img.crossOrigin = 'Anonymous';
  
  img.onload = function(){
      canvas.height = img.height;
      canvas.width = img.width;
      ctx.drawImage(img, 0, 0);
      var dataURL = canvas.toDataURL();
      setBreakpoint(dataURL);
      callback.call(this, dataURL);
      canvas = null;
  };
  
  img.src = url;
  </code></pre>