1.3.0 • Public • Published


    image-resizer is a Node.js application that sits as a custom origin to your CDN and will resize/optimise images on-the-fly. It is Heroku ready, but can also be deployed easily to any cloud provider (has been used with success on AWS).

    The primary goal for this project was to abstract the need to set image dimensions during the upload and storage phase of images in a modern web application.


    Building and deploying your own version of image-resizer is as easy as running the cli tool (image-resizer new), setting your Heroku configs and firing it up!

    Based on Express.js image-resizer uses sharp under the hood to modify and optimise your images.

    There is also a plugin architecture that allows you to add your own image sources. Out of the box it supports: S3, Facebook, Twitter, Youtube, Vimeo (and local file system in development mode).

    When a new image size is requested of image-resizer via the CDN, it will pull down the original image from the cloud. It will then resize according to the requested dimensions, optimize according to file type and optionally filter the image. All responses are crafted with custom responses to maximise the facility of the CDN.

    Getting Started

    $ npm install -g image-resizer gulp
    $ mkdir my_fancy_image_server
    $ cd my_fancy_image_server
    $ image-resizer new
    $ npm install
    $ gulp watch

    This will create a new directory structure including all the necessary files needed to run image-resizer. The money file is index.js which is loads the express configuration and routes.

    image-resizer can also simply be added as a node_module to any project and the streams interfaces used standalone. ./test.js has a good example of how the app should work running behind Express.

    There is a RubyGem of helpers (both Ruby and Javascript) to assist you in building the endpoints for your image-resizer instance.


    The new refactored codebase now takes advantage of node streams. The previous iteration was heavily based on promises but still ended up with spaghetti code to some extent.

    Inspired a lot by Gulp image-resizer passes around an Image object between each of the streams that contains information about the request and the image data (either as a buffer or stream).

    Images are also no longer modified and sent back to s3 for storage. The full power of the CDN is used for storing the modified images. This greatly improves performance both on the server side and client side. Google PageSpeed did not like the 302 redirects returned by an image-resizer instance.

    Also removing the need to push data to s3 helps the server processing as this can be a wildly inconsistent action.


    image-resizer now supports a range of custom plugins for both image sources and filters. As mentioned above a number of sources are supported out of the box but each of these can be over written as needed.

    The directory structure created via $ image-resizer new will include a plugins directory where the initialization script will pick up any scripts and insert them into the application.


    image-resizer only requires a working node/npm environment and libvips. The necessary buildpack information to load your Heroku environment is included.

    Environment Variables

    Configuration of image-resizer is done via environment variables. This is done to be compatible with Heroku deployments.

    To set environment variables in your Heroku console.

    heroku config:set AWS_ACCESS_KEY_ID=abcd1234

    For Heroku deployment the minimum required variables are:


    If you choose to change your default source to be something other than S3 then the NODE_ENV variable is the only required one (and whatever you need for your default source).

    For convenience in local and non-Heroku deployments the variables can be loaded from a .env file. Sensible local defaults are included in src/config/environment_vars.js.

    The available variables are as follows:

      NODE_ENV: 'development',
      PORT: 3001,
      DEFAULT_SOURCE: 's3',
      EXCLUDE_SOURCES: null, // add comma delimited list
      // Restrict to named modifiers strings only
      // AWS keys
      AWS_ACCESS_KEY_ID: null,
      AWS_REGION: null,
      S3_BUCKET: null,
      // Resize options
      AUTO_ORIENT: true,
      REMOVE_METADATA: true,
      // Protect original files by specifying a max image width or height - limits
      // max height/width in parameters
      // Color used when padding an image with the 'pad' crop modifier.
      IMAGE_PADDING_COLOR: 'white',
      // Optimization options
      IMAGE_QUALITY: 80,
      // Cache expiries
      IMAGE_EXPIRY: 60 * 60 * 24 * 90,
      IMAGE_EXPIRY_SHORT: 60 * 60 * 24 * 2,
      JSON_EXPIRY: 60 * 60 * 24 * 30,
      // Logging options
      LOG_PREFIX: 'resizer',
      QUEUE_LOG: true,
      // Response settings
      CACHE_DEV_REQUESTS: false,
      // Twitter settings
      // Where are the local files kept?
      LOCAL_FILE_PATH: process.cwd(),
      // Display an image if a 404 request is encountered from a source
      IMAGE_404: null
      // Whitelist arbitrary HTTP source prefixes using EXTERNAL_SOURCE_*


    Optimization of images is done via sharp. The environment variables to set are:

    • IMAGE_QUALITY: 1 - 100
    • IMAGE_PROGRESSIVE: true | false

    You may also adjust the image quality setting per request with the q quality modifier described below.


    While image-resizer will work as a standalone app, almost all of its facility is moot unless you run it behind a CDN. This has only been run behind AWS Cloudfront at this point and consequently all of the response headers are customized to work best in that environment. However other CDN's can not operate much differently, any pull requests in this regard would be most appreciated ;-)


    A couple of routes are included with the default app, but the most important is the image generation one, which is as follows:[:format][:metadata]

    Modifiers are a dash delimited string of the requested modifications to be made, these include:

    Supported modifiers are:

    • height: eg. h500
    • width: eg. w200
    • square: eg. s50
    • crop: eg. cfill
    • top: eg. y12
    • left: eg. x200
    • gravity: eg. gs, gne
    • filter: eg. fsepia
    • external: eg. efacebook
    • quality: eg. q90

    Crop modifiers:

    • fit
      • maintain original proportions
      • resize so image fits wholly into new dimensions
        • eg: h400-w500 - 400x600 -> 333x500
      • default option
    • fill
      • maintain original proportions
      • resize via smallest dimension, crop the largest
      • crop image all dimensions that dont fit
        • eg: h400-w500 - 400x600 -> 400x500
    • cut
      • maintain original proportions
      • no resize, crop to gravity or x/y
    • scale
      • do not maintain original proportions
      • force image to be new dimensions (squishing the image)
    • pad
      • maintain original proportions
      • resize so image fits wholly into new dimensions
      • padding added on top/bottom or left/right as needed (color is configurable)


    • - original image request, will be optimized but not resized

    Resizing Logic

    It is worthy of note that this application will not scale images up, we are all about keeping images looking good. So a request for h400 on an image of only 200px in height will not scale it up.

    S3 source

    By default image-resizer will use s3 as the image source. To access an s3 object the full path of the image within the bucket is used, minus the bucket name eg:

    translates to:

    External Sources

    It is possible to bring images in from external sources and store them behind your own CDN. This is very useful when it comes to things like Facebook or Vimeo which have very inconsistent load times. Each external source can still enable any of the modification parameters list above.

    In addition to the provided external sources, you can easily add your own basic external sources using EXTERNAL_SOURCE_* environment variables. For example, to add Wikipedia as an external source, set the following environment variable:


    Then you can request images beginning with the provided path using the ewikipedia modifier, eg:

    translates to:

    It is worth noting that Twitter requires a full set of credentials as you need to poll their API in order to return profile pics.

    A shorter expiry on images from social sources can also be set via IMAGE_EXPIRY_SHORT env var so they expiry at a faster rate than other images.

    It is also trivial to write new source streams via the plugins directory. Examples are in src/streams/sources/.

    Output format

    You can convert images to another image format by appending an extra extension to the image path:


    JPEG (.jpg/.jpeg), PNG (.png), and WEBP (.webp) output formats are supported.

    Metadata requests

    image-resizer can return the image metadata as a json endpoint:


    Metadata is removed in all other image requests by default, unless the env var REMOVE_METADATA is set to false.

    Heroku Deployment

    Included are both a .buildpacks file and a Procfile ready for Heroku deployment. Run the following cmd in your Heroku console to enable the correct buildpacks (copied from here).

    heroku config:set BUILDPACK_URL=

    The .buildpacks file will then take care of the installation process.

    As mentioned above there is a minimum set of config vars that need to be set before image-resizer runs correctly.

    It is also of note that due to some issues with GCC, sharp can not be used on the older Heroku stacks. Currently it requires cedar-14 stack.

    Local development

    To run image-resizer locally, the following will work for an OSX environment assuming you have node/npm installed - NVM is useful.

    npm install gulp -g
    npm install
    gulp watch

    The gulp setup includes nodemon which runs the app nicely, restarting between code changes. PORT can be set in the .env file if you need to run on a port other than 3001.

    Tests can be run with: gulp test

    Early promise-based version of codebase

    NOTE: Completely refactored and improved, if you are looking for the older version it is tagged as v0.0.1.


    npm i image-resizer

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