image is not converting in php
===

My code to convert planets.png to planets.jpg

    <?php 
    exec("convert planets.png planets.jpg");
    ?>

Which is not working just showing blank page.

i have installed imagemagick as it is showing in phpinfo() [View here][1]

Is here any other configuration remaining to run that imagemagick code.


  [1]: http://i.stack.imgur.com/IRJlG.png