[JavaScript] get Image true size

// get Image true size
var img_true_size = function(image){
	var	w = image.width ,
		h = image.height ;

	if ( "naturalWidth" in image ) {	// for Firefox, Safari, Chrome
		w = image.naturalWidth;
		h = image.naturalHeight;

	} else if ( typeof image.runtimeStyle !== 'undefined' ) {	 // for IE
		var run = image.runtimeStyle;
		var mem = { w: run.width, h: run.height };	// keep runtimeStyle
		run.width  = "auto";
		run.height = "auto";
		w = image.width;
		h = image.height;
		run.width  = mem.w;
		run.height = mem.h;

	} else {		 // for Opera
		var mem = { w: image.width, h: image.height };	// keep original style
		image.removeAttribute("width");
		image.removeAttribute("height");
		w = image.width;
		h = image.height;
		image.width  = mem.w;
		image.height = mem.h;
	}

	return {width:w, height:h};
}

via. http://d.hatena.ne.jp/uupaa/20090602/1243933843