var defaultwidth = 640;

function MinimizeImg(element,size,imagewidth,imageheight) {	
		if(imagewidth>size) {
			element.width	= size;
			element.height = size/imagewidth*imageheight;
		} else {
			element.height = size;
			element.width = size/imageheight*imagewidth;		
		}
	}
	
function ToggleZoom(element,imagewidth,imageheight) {
    if(imageheight>imagewidth) {
        origsize = imageheight;
        actualsize = element.height;
    } else {
        origsize = imagewidth;
        actualsize = element.width;
    }
    // Zoomen
    if(actualsize < origsize) {
        element.width = imagewidth;
        element.height = imageheight;
    } else
        MinimizeImg(element,defaultwidth,imagewidth,imageheight);
}