Ogre Forums

At this time, there is no way to safely dump floating-point image formats without converting them to a lesser format and truncating valuable information.
http://www.graphics.cornell.edu/online/formats/rgbe/

That link has some code that can easily be adapted to the Ogre pixel formats with very little change.

If you are in actual need of that feature, you might want to try to add it yourself and then submit a patch. Otherwise you will have to wait for someone to pick it up. I would also advice you to create a ticket on our tracker for that.