Create a darken version of an image

Question

I need to create a darken version of an image. What is the correct way to accomplish this? I have tried with the 'modulate' method:

manipulate! do |img|
  img.modulate(0.85)
end

but the result is not optimal (see Result link).

Original Result

Answer 1

RMagick Transformation Script has a darken method which may be better suited to this:

img.darken      # darkens the image 25%.
img.darken 0.40 # darkens the image 40%.