image rollover problems

[Jago6060]

my code is set so I can enlarge the images but they don't retain their original proportions.  Anyone know how I can keep the image proportions?

 

heres my function...

 

<script language="JavaScript">
function imgEnlarge(obj){
   obj.height += 150;
   obj.width += 150;
}
function imgShrink(obj){
   obj.height -= 150;
   obj.width -= 150;
}
</script>

[mainewoods]

try just setting the height and set the width to blank(it works in html):

function imgEnlarge(obj){
      obj.width = '';
      obj.height += 150;
}
function imgShrink(obj){
    obj.width = '';
    obj.height -= 150;
   
}