PHP Convert jp2 to jpeg output

Question

Using strictly the gmagick or imagick libraries for PHP I am trying to convert jpeg2000 data to browser-compatible jpeg. The jp2 works fine, but trying to convert to jpeg seems to just return the same data, no conversion being done.

 $image = new Gmagick($_img->getImageBlob());
 $image->setImageFormat("jpeg");
 Header("Content-type: image/jpeg");
 echo $image;

$_img contains the input jp2 data. I want to avoid using exec for conversion using the system library to make this platform independent.