如何在WebKit瀏覽器中準確取得真實影像尺寸？

var img = $("img")[0]; // Retrieve the image element
var pic_real_width, pic_real_height;

$("<img/>") // Create an in-memory copy to prevent CSS interference
    .attr("src", $(img).attr("src"))
    .load(function() {
        pic_real_width = this.width; // Note: $(this).width() won't work for in-memory images.
        pic_real_height = this.height;
    });

var pic_real_width = img.naturalWidth;
var pic_real_height = img.naturalHeight;