Libraries

Adding custom Active Storage transformations

Curated ago by @jeremysmithco

Description

Out of the box, Active Storage supports a number of transformations, through the image_processing gem. This gem provides a common interface to both MiniMagick (the old standard) and ruby-vips (the new default).

I recently needed the ability to lighten images uploaded via Active Storage (for use as watermarks), but there isn’t a built-in method to do this through the transformations interface. However, I discovered that you can register your own custom ImageProcessing methods like this. (Thanks to this blog post for the approach.)

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require 'image_processing'

module ImageProcessing::Vips::CustomProcessing
  extend ActiveSupport::Concern

  included do
    def lighten(percentage)
      overlay = image.new_from_image([255, 255, 255, (255 * percentage).to_i])
      image.composite(overlay, :over)
    end
  end
end

Create a custom module to be included in the processor, adding a lighten method. The image is an accumulator available to all methods in the processing pipeline. The new_from_image method creates a new image of the same dimensions as the original, setting every pixel to RGB value (255, 255, 255) or white, with an opacity set to the percentage argument. Then this overlay image is “composited” over the original image with the composite method.