function nextImage() {
	var new_num = document.getElementById("img_num").innerHTML;
	var max_num = document.getElementById("img_max_num").innerHTML; 	

	new_num++;
		
	if (new_num > max_num) {
		new_num = 1;	
	}
	
	var newSrc = "graphics/lab_images/img" + new_num + "_sm.jpg";
   	document.getElementById("slideshow_img").src = newSrc;					
	document.getElementById("img_num").innerHTML = new_num;
	
	var newLink = "graphics/lab_images/img" + new_num + ".jpg";
	document.getElementById("img_full_view").href = newLink;
	
	changeDesc();
}

function prevImage() {
	var new_num = document.getElementById("img_num").innerHTML; 	
	var max_num = document.getElementById("img_max_num").innerHTML;
	
	new_num--;
		
	if (new_num < 1) {
		new_num = max_num;	
	}
	
	var newSrc = "graphics/lab_images/img" + new_num + "_sm.jpg";
   	document.getElementById("slideshow_img").src = newSrc;					
	document.getElementById("img_num").innerHTML = new_num;
	
	var newLink = "graphics/lab_images/img" + new_num + ".jpg";
	document.getElementById("img_full_view").href = newLink;
	
	changeDesc();
}

function changeDesc() {
    var num = document.getElementById("img_num").innerHTML;
	var text_all = document.getElementById("img_desc").innerHTML;
	
	var begin = text_all.indexOf(num);
	var end = text_all.indexOf(";", begin);
	
	var desc = text_all.substr(begin + 3, end - begin - 3);
	
	document.getElementById("img_description_text").innerHTML = desc;
}