if (document.images) {
buttonUp = new Image(); buttonUp.src = "images/button_col_.png"; // Never use bitmaps for the web.
buttonDown = new Image(); buttonDown.src = "images/button_col_OVER.png";
}

function turn_off(cell) {
if (document.images != null) {
cell.style.backgroundImage = "url('" + buttonUp.src + "')";
}
}

function turn_on(cell) {
if (document.images != null) {
cell.style.backgroundImage = "url('" + buttonDown.src + "')";
}
}