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Need to handle image uploads in your Rails app? Give DynamicImage a try.

Rather than creating a pre-defined set of images when a file is uploaded, DynamicImage stores the original file and generates images on demand. It handles cropping, resizing, format and colorspace conversion.

Supported formats at the moment are JPEG, PNG, GIF, BMP, WebP and TIFF. BMP, WebP and TIFF images will automatically be converted to JPG. CMYK images will be converted to RGB, and RGB images will be converted to the sRGB colorspace for consistent appearance in all browsers.

DynamicImage is built on Dis and ruby-vips.

All URLs are signed with a HMAC to protect against denial of service and enumeration attacks.


  • Rails 5+
  • Ruby 2.7+
  • libvips 8.8+


Documentation is available on


Add the gem to your Gemfile and run bundle install.

gem "dynamic_image", "~> 3.0"

Run the dis:install generator to set up your storage.

bin/rails generate dis:install

You can edit the generated initializer to configure your storage, by default it will store files in db/dis. See the Dis documentation for more information.

Creating your resource

Run the dynamic_image:resource generator to create your resource.

bin/rails generate dynamic_image:resource image

This will create an Image model and a controller, along with a migration and the necessary routes.

Note that in this case, the route with collide with any static images stored in public/images. You can customize the path if you want in the route declaration.

image_resources :images, path: "dynamic_images/:digest(/:size)"

Storing an image

To save an image, simply assign the file attribute to your uploaded file.

image_params = params.require(:image).permit(:file)

Rendering images in your views

You should use the provided helpers for displaying images, this will ensure that the generated URLs are properly signed and timestamped.

To display the image at it's original size, use dynamic_image_tag without any options.

<%= dynamic_image_tag(image) %>

To resize it, specify a max size. This will scale the image down to fit, but no cropping will occur.

<%= dynamic_image_tag(image, size: "400x400") %>

Setting crop: true will crop the image to the exact size.

<%= dynamic_image_tag(image, size: "400x400", crop: true) %>

Omitting either dimension will render the image at an exact width or height.

<%= dynamic_image_tag(image, size: "400x") %>

dynamic_image_path and dynamic_image_url act pretty much like regular URL helpers.

<%= link_to "See image", dynamic_image_path(image) %>


Generating images on the fly is expensive. This is less of a problem in development mode, as DynamicImage respects the If-Modified-Since header. In production, you should absolutely cache the results.

DynamicImage doesn't do any caching on it's own, but it is designed to play well with others. Here's a few options:

It's perfectly safe to cache images indefinitely. The URL is timestamped, and will change if the object changes.


Copyright 2006-2016 Inge Jørgensen

DynamicImage is released under the MIT License.