def convert(format)
      ptr = ZBar.zbar_image_convert(@img, format)
      if ptr.null?
        raise ArgumentError, "conversion failed"
      else
        Image.new(ptr)
      end
    end
def convert(format)
      ptr = ZBar.zbar_image_convert(@img, format)
      if ptr.null?
        raise ArgumentError, "conversion failed"
      else
        Image.new(ptr)
      end
    end
Ask ZBar to convert this image to a new format, returning a new Image.

 Not all conversions are possible: for example, if ZBar was built without
 JPEG support, it cannot convert JPEGs into anything else.