def center_crop(dimensions, upsample)
      if is_smaller_than(dimensions) && upsample == false
        dimensions = reduce_to_image(dimensions)
      end
      image_file.thumb("#{dimensions_to_string(dimensions)}#")
    end
def center_crop(dimensions, upsample)
      if is_smaller_than(dimensions) && upsample == false
        dimensions = reduce_to_image(dimensions)
      end
      image_file.thumb("#{dimensions_to_string(dimensions)}#")
    end
Uses imagemagick to make a centercropped thumbnail. Does not scale the image up.