function showimg1(){
document.area1.src = "top/top_image_tri.jpg";
}

function showimg2(){
document.area1.src = "top/top_image_bkp.jpg";
}

function showimg3(){
document.area1.src = "top/top_image_blp.jpg";
}

function showimg4(){
document.area1.src = "top/top_image.jpg";
}