gistfile1.rb

class GenericFile < ActiveFedora::Base
  ...
  
      makes_derivatives_of :content, based_on: :mime_type do
        'text/pdf' =>                 { derivatives: { :text => { :quality => :better },
                                        processors: [:ocr]}},
        ['image/png', 'image/jpg'] => { derivatives: { :medium => "300x300>", :thumb => "100x100>" }}
      end
  
end