def split_images
  #'image' is a ImageMagick Object
  width  = image.cols/number_cols
  height = image.rows/nubmer_rows
  images = []
  0.upto(number_rows-1) do |x|
    0.upto(number_cols-1) do |y|
      images << image.crop( Magick::NorthWestGravity, x*width, y*height, width, height, true)
    end
  end
end