Although I know TIFF is not really a web-friendly format, I have a need to put TIFF files on a wiki, with thumbnails in PNG or JPEG format. I can upload files without any trouble but thumbnails are not created.

This is mediawiki 1.11. It's not a matter, as far as I can tell, of file size (the file I tested with wasn't all that big). Further, the mime type is correctly discovered by mediawiki. I found an error in the log about there not being a media handler for tiff files. Indeed, the $wgMediaHandlers array (in /includes/DefaultSettings.php) does not include anything for TIFF files. I tried adding an entry to the array by placing this line in LocalSettings.php.

$wgMediaHandlers['image/tiff'] = 'BitmapHandler' ;

That clearly was not right. Now I get a properly sized image box on my wiki page but it says "Error creating thumbnail: Invalid thumbnail parameters". So, BitmapHandler is wrong. Is there any right handler for tiff images are are they not supported? Thanks for your help.