If you're using GD library, try using imagecopyresampled() if you're not yet. It will not give you amazing results though. You'll need external software for the best results.

Hi php_daemon,

Thanks for your great reply. I have used the imagecopyresampled, but it is used to changed the picture size statically. i need to be change the size of the picture dynamically such as while pressing the zoomin button continously the picture size goes increasingly simultaneoulsy. Is there any possible idea for it?

Thanks

You could put AJAX to work.