Convert image png to jpg with Magento

i try to convert an image png in jpg in a custom module with Magento. The upload works but when i try to convert the pic there is a prblm. There isn't method to convert in the Varien_file_uploader but in the Varien_image there is. I try that :

$uploader = new Varien_File_Uploader('image');              
$uploader->setAllowedExtensions(array('jpg','png','gif','jpeg'));
$uploader->setAllowRenameFiles(false);
$uploader->setFilesDispersion(false);
$uploader->save($path, $_FILES['image']['name']);   

$image = new Varien_Image($path . DS . $_FILES['image']['name']);
$image->convert('jpeg');
$image->save($path, 'mypic.jpeg');

Any ideas ? Thx