等比例缩小图片

//等比例缩小图片
function changeImg(obj,width,height) { 
 
    var img = new Image();
    img.src = document.getElementById(obj.id).src
    var ys_w = img.width;
    var ys_h = img.height;       
   
    if(ys_w > width || ys_h > height)       
    {
        var scale;
        var scale1 = ys_w / width;
        var scale2 = ys_h / height;  
        //alert(scale1+","+scale2);
        if(scale1 > scale2)
        {
            scale = scale1;
        }
        else
        {
            scale = scale2;
        }
       document.getElementById(obj.id).style.width = ys_w / scale;
       document.getElementById(obj.id).style.height = ys_h / scale;  
    }
}