function pngON(img){img.src="images/" + img.id + "_on.png"}
function pngOFF(img){img.src="images/" + img.id + ".png"}

function jpgON(img){img.src="images/" + img.id + "_on.jpg"}
function jpgOFF(img){img.src="images/" + img.id + ".jpg"}

function gifON(img){img.src="images/" + img.id + "_on.gif"}
function gifOFF(img){img.src="images/" + img.id + ".gif"}