如下是我的全部代码，在谷歌浏览器中运行，但是canvas就是画不出图片。求大神指点，哪里写的有问题？
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div id="root">
</div>
<img id="preview" src="http://img02.tooopen.com/images/20140504/sy_60294738471.jpg" />
<script>
var img = document.getElementById('preview');
document.getElementById('root').appendChild(convertImageToCanvas(img));
function convertImageToCanvas(image) {
var canvas = document.createElement("canvas");
canvas.setAttribute('style','border:1px solid #000');
canvas.getContext("2d").drawImage(image, 0, 0);
canvas.width = image.width;
canvas.height = image.height;
return canvas;
}
</script>
</body>
</html>
