jquery 获取上传图片的宽高和预览图

<script src="http://libs.baidu.com/jquery/2.0.0/jquery.js"></script>

<input name="pic" id="pic" class="txt_form" type="file"><span id="pic_info" style="color:red;"></span>
<img src="" alt="" id="lod_pic" width="580" >

  $('#pic').change(function(){
var file = this;
createReader(file.files[0], function (w, h, u) { 
// alert(w + ' '+ h +' '+u);
$('#lod_pic').attr("src",u);
$('#pic_info').text("（图片尺寸："+w+"x"+h+"）");
});
  })
createReader = function(file, whenReady) {
    var reader = new FileReader;
    reader.onload = function (evt) {
        var image = new Image();
        image.onload = function () {
        var pic_url = this.src;
            var width  = this.width;
            var height = this.height;
            if (whenReady) whenReady(width, height , pic_url);
        };
        image.src = evt.target.result;
    };
    reader.readAsDataURL(file);
}