Javascript popup window

[klassic]

I have a java script popup window created to display a larger image of our products. Right now it has a specified Height and Width. I was wondering if there was any way to make the height and width dependent on the size of the image. Some of our images have more height than width, and others more width than height.

Or if the H & W can't be dynamic like that I would just like to center the image in the popup window.

Here is a link to one of our products for reference to what I already have enabled. Contrast Hoodie (http://www.greekave.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=ss21985)
Click on the image or text below it to view the larger image.

[DesignExtend-MSI]

Here's a resource for doing something like this:

http://www.codelifter.com/main/javascript/autosizeimagepopup.html