Rails 6 - Shrine - ImageProcessing - Get Original Uploaded file

This is my image_uploader.rb

require "image_processing/mini_magick"

    class ImageUploader < Shrine


    Attacher.derivatives do |original|
        magick = ImageProcessing::MiniMagick.source(original).saver(quality: 88)
        # generate the thumbnails you want here 
        { 
         thumb:  magick.resize_to_fill!(150, 150),
         medium: magick.resize_to_fill!(500, 500),
         large:  magick.resize_to_limit!(800, 800),
        }
    end


end

Question is simple but I can't find answer is Shrine docs. How can I get original photo ? In Rails 4 it was simple, I just ask for image_url(:original)

SOME TRICK:

I read about mini_magic and add something like this

 original: magick.resize_to_limit!(20000,20000),

Image won't be changed if do not exceed 20000x20000 dimensions ...