A quick and dirty sprockets extension example to transform images between formats.

sprockets.rb

# config/initializers/sprockets.rb
class ImageTransformer
  def call(input)
    filename, content_type = input.values_at(:filename, :content_type)
    new_extension = content_type.split('/').last
    converted = ImageProcessing::Vips.source(filename).convert!(new_extension)
    { data: converted.read, charset: nil }
  ensure
    converted&.unlink
  end
end

Sprockets.register_transformer('image/jpeg', 'image/webp', ImageTransformer.new)