class ActiveStorage::Variation

def transform(image)

and performs the +transformations+ against it. The transformed image instance is then returned.
Accepts an open MiniMagick image instance, like what's returned by MiniMagick::Image.read(io), 
def transform(image)
  ActiveSupport::Notifications.instrument("transform.active_storage") do
    transformations.each do |name, argument_or_subtransformations|
      image.mogrify do |command|
        if name.to_s == "combine_options"
          argument_or_subtransformations.each do |subtransformation_name, subtransformation_argument|
            pass_transform_argument(command, subtransformation_name, subtransformation_argument)
          end
        else
          pass_transform_argument(command, name, argument_or_subtransformations)
        end
      end
    end
  end
end