def to_ps(options={})
      output_to_string_io do |io|
        Cairo::PSSurface.new(io,
                             full_width(options),
                             full_height(options)) do |surface|
          surface.eps = options[:eps] if surface.respond_to?(:eps=)
          render(surface, options)
        end
      end
    end
def to_ps(options={})
      output_to_string_io do |io|
        Cairo::PSSurface.new(io,
                             full_width(options),
                             full_height(options)) do |surface|
          surface.eps = options[:eps] if surface.respond_to?(:eps=)
          render(surface, options)
        end
      end
    end
Render the barcode to a PS document