function resize_image_by_id(image_id, sizw, sizh)
{
    var i = document.getElementById(image_id);
    resize_image(i, sizw, sizh)
}
function resize_image(image, sizw, sizh)
{
    if (!sizw) sizw = 100;
    if (!sizh) sizh = 100;
    if (image.width >= image.height)
        if (image && image.width > sizw)
        {
        	var new_width = sizw;
        	var new_height = (image.height * sizw) / image.width;
        	image.width = new_width;
        	image.height = new_height;
        }
    else
        if (image && image.height > sizh)
        {
        	var new_height = sizh;
        	var new_width = (image.width * sizh) / image.height;
        	image.width = new_width;
        	image.height = new_height;
        }
}

function toggle_image_by_id(image_id, mode)
{
    var i = document.getElementById(image_id);
    if (mode && mode == "show" ) show_image(i);
    else 
        if (mode && mode == "hide" ) hide_image(i);
        else 
            if (i && i.style.display == "block") hide_image(i);
            else show_image(i);
}
function show_image(image)
{
    if (image) image.style.display = "block";
}

function hide_image(image)
{
    if (image) image.style.display = "none";
}

function show_next(oldn, newn)
{
    if (newn == "next") newn = oldn + 1;
    if (newn == "prev") newn = oldn - 1;
    var old_id = "screen_" + oldn + "_large";
    var new_id = "screen_" + newn + "_large";
    toggle_image_by_id(old_id, "hide");
    toggle_image_by_id(new_id, "show");
}