function f_enlargeimage(product_img_id) {
	thumbimg_new = document.getElementById('product_img_1').src;
	mainimg_new = document.getElementById(product_img_id).src;

	// set thumbnail to current main image (swap f for m)
	document.getElementById(product_img_id).src = thumbimg_new.replace("/f","/m");
	// set main image to selected thumb image (swap m for f)
	document.getElementById('product_img_1').src = mainimg_new.replace("/m","/f");
}