var hoverImage = "url(images/link_hover.jpg)";
  var normalImage = "url(images/link_normal.jpg)";

function changeHover1() {
document.getElementById('link1').style.backgroundImage = hoverImage;
}
function changeNormal1() {
document.getElementById('link1').style.backgroundImage = normalImage;
}

function changeHover2() {
document.getElementById('link2').style.backgroundImage = hoverImage;
}
function changeNormal2() {
document.getElementById('link2').style.backgroundImage = normalImage;
}

function changeHover3() {
document.getElementById('link3').style.backgroundImage = hoverImage;
}
function changeNormal3() {
document.getElementById('link3').style.backgroundImage = normalImage;
}

function changeHover4() {
document.getElementById('link4').style.backgroundImage = hoverImage;
}
function changeNormal4() {
document.getElementById('link4').style.backgroundImage = normalImage;
}

function changeHover5() {
document.getElementById('link5').style.backgroundImage = hoverImage;
}
function changeNormal5() {
document.getElementById('link5').style.backgroundImage = normalImage;
}

function changeHover6() {
document.getElementById('link6').style.backgroundImage = hoverImage;
}
function changeNormal6() {
document.getElementById('link6').style.backgroundImage = normalImage;
}
  
function changeHover7() {
document.getElementById('link7').style.backgroundImage = hoverImage;
}
function changeNormal7() {
document.getElementById('link7').style.backgroundImage = normalImage;
}

function changeHover8() {
document.getElementById('link8').style.backgroundImage = hoverImage;
}
function changeNormal8() {
document.getElementById('link8').style.backgroundImage = normalImage;
} 


  var subhoverImage = "url(images/sublink_hover.jpg)";
  var subnormalImage = "url(images/sublink_normal.jpg)";

function changesubHover1() {
document.getElementById('sublink1').style.backgroundImage = subhoverImage;
}
function changesubNormal1() {
document.getElementById('sublink1').style.backgroundImage = subnormalImage;
}

function changesubHover2() {
document.getElementById('sublink2').style.backgroundImage = subhoverImage;
}
function changesubNormal2() {
document.getElementById('sublink2').style.backgroundImage = subnormalImage;
}

function changesubHover3() {
document.getElementById('sublink3').style.backgroundImage = subhoverImage;
}
function changesubNormal3() {
document.getElementById('sublink3').style.backgroundImage = subnormalImage;
}

function changesubHover4() {
document.getElementById('sublink4').style.backgroundImage = subhoverImage;
}
function changesubNormal4() {
document.getElementById('sublink4').style.backgroundImage = subnormalImage;
}