validation not working with file_column

I have installed the file_column plugin: in my model i have this code:

validates_file_format_of :image, :in => ["gif", "png", "jpg"], :message => 'must be an image file'   validates_filesize_of :image, :in => 0..800.kilobytes, :too_large_message => 'mettine una + piccola'

  file_column :image,:magick=>{       :geometry=>'600x600>',:attributes => { :quality => 60 },       :versions => {         :thumb => {:crop => "1:1", :geometry =>"30x30",:attributes => { :quality => 50 } },         :thumb_big=>{:crop => "1:1", :geometry =>"62x62",:attributes => { :quality => 50 } }       }   }

validates_filesize_of not works.

Why? How i can do? Thanks