Workaround for toDataURL >2MB

gistfile1.txt

//From https://code.google.com/p/chromium/issues/detail?id=69227#c37

//take apart data URL
var parts = canvas.toDataURL().match(/data:([^;]*)(;base64)?,([0-9A-Za-z+/]+)/);

//assume base64 encoding
var binStr = atob(parts[3]);

//convert to binary in ArrayBuffer
var buf = new ArrayBuffer(binStr.length);
var view = new Uint8Array(buf);
for(var i = 0; i < view.length; i++)
  view[i] = binStr.charCodeAt(i);

var blob = new Blob([view], {'type': parts[1]});
var URL = webkitURL.createObjectURL(blob)