def transformation_command
      scale, crop = @current_geometry.transformation_to(@target_geometry, crop?)
      trans = []
      trans << "-resize" << %["#{scale}"] unless scale.nil? || scale.empty?
      trans << "-crop" << %["#{crop}"] << "+repage" if crop
      trans
    end
def transformation_command
      scale, crop = @current_geometry.transformation_to(@target_geometry, crop?)
      trans = []
      trans << "-resize" << %["#{scale}"] unless scale.nil? || scale.empty?
      trans << "-crop" << %["#{crop}"] << "+repage" if crop
      trans
    end
Returns the command ImageMagick's +convert+ needs to transform the image
 into the thumbnail.