require 'rmagick'

img = Magick::Image.read('images/Flower_Hat.jpg').first
begin
  img = img.level_colors('green', 'orange', true)
  img.alpha(Magick::DeactivateAlphaChannel)
rescue NotImplementedError
  not_imp = Magick::Image.read('images/notimplemented.gif').first
  img = not_imp.resize(img.columns, img.rows)
end
img.write('level_colors.jpg')