How to apply a transformation to all image versions (Carrierwave)?

To apply a transformation to all image versions, you can use process_all_versions in Carrierwave.

Here's an example of applying a 'sepia' effect to all versions (the rest is not required, it's a demo only):

class PictureUploader < CarrierWave::Uploader::Base

  include Cloudinary::CarrierWave

  process_all_versions :cloudinary_transformation => {:effect => :sepia}

  process :tags => ['post_picture']

  version :standard do
    process :resize_to_fill => [100, 150, :north]
  end

  version :thumbnail do
    resize_to_fit(50, 50)
  end

end