gistfile1.txt

    # * +convert_options+: When creating thumbnails, use this free-form options
    #   field to pass in various convert command options.  Typical options are "-strip" to
    #   remove all Exif data from the image (save space for thumbnails and avatars) or
    #   "-depth 8" to specify the bit depth of the resulting conversion.  See ImageMagick
    #   convert documentation for more options: (http://www.imagemagick.org/script/convert.php)
    #   Note that this option takes a hash of options, each of which correspond to the style
    #   of thumbnail being generated. You can also specify :all as a key, which will apply
    #   to all of the thumbnails being generated. If you specify options for the :original,
    #   it would be best if you did not specify destructive options, as the intent of keeping
    #   the original around is to regenerate all the thumbnails when requirements change.
    #     has_attached_file :avatar, :styles => { :large => "300x300", :negative => "100x100" }
    #                                :convert_options => {
    #                                  :all => "-strip",
    #                                  :negative => "-negate"
    #                                }