- derivative fix floating point rounding errors for certain sizes

- increase derivative size for which metadata is kept
- imagick use 4:2:2 chroma subsampling (reduce file size by 20-30% with "almost" no human perception)
- dont show mobile theme links if there is no mobile theme installed
- mobile theme favicon removed because 404

git-svn-id: http://piwigo.org/svn/trunk@13426 68402e56-0260-453c-a942-63ccdbb3a9ee

admin/include/image.class.php

@@ -458,6 +458,8 @@ class image_imagick implements imageInterface
 
   function write($destination_filepath)
   {
+    // use 4:2:2 chroma subsampling (reduce file size by 20-30% with "almost" no human perception)
+    $this->image->setSamplingFactors( array(2,1) );
     return $this->image->writeImage($destination_filepath);
   }
 }