On the docs page, in Chrome, hit ctrl+shift+J (option+cmd+J on OSX) to open the console, and paste this in:

$('canvas').click(function() { window.open( this.toDataURL("image/png") , 'Serialized Canvas' , 'height=' + this.height + 'width=' + this.width ); });

This will popup a png version of a canvas graph if you click it.