unpic

🖼 Unpic

Universal image CDN URL translator

There are many image CDNs that provide a URL API for transforming images. There is little consistency in these APIs, and it's often unclear what the API is for a given URL. This library aims to provide a consistent interface for detecting image CDN URLs and transforming them.

If you'd like to use this on the web, you might want to try Unpic img, a multi-framework image component, powered by Unpic.

It designed to work with image URLs from sources such as CMSs and other user-generated content, where the source image may or may not be from an image CDN, and may already have transforms applied. This allow different transforms to be applied for display on a website. A web framework may need to transform an image for display on a site. Rather than doing this by downloading and resizing it locally or re-processing it with a separate image service, this library can be used to transform the URL to use the original image CDN, which will then transform the image on the fly.

Usage

This library is available via NPM as unpic and JSR as @unpic/lib.

To use it in Node, install it from npm:

npm install unpic

Then import it in your code:

import { transformUrl } from "unpic";

To use it in Deno, import the module from JSR:

import { transformUrl } from "jsr:@unpic/lib";

If you previously installed the library from deno.land/x, you should update to use JSR instead as the deno.land/x version is no longer updated.

You can then use the transformUrl function to transform a URL:

const url = transformUrl(
	"https://cdn.shopify.com/static/sample-images/bath_grande_crop_center.jpeg",
	{
		width: 800,
		height: 600,
	},
);

console.log(url);
// https://cdn.shopify.com/static/sample-images/bath.jpeg?width=800&height=600&crop=center

You can also use the parseUrl function to parse a URL and get information about the image:

const parsed = parseUrl(
	"https://cdn.shopify.com/static/sample-images/bath_800x600_crop_center.jpeg",
);

console.log(parsed);
// {
//   provider: "shopify",
//   src: "https://cdn.shopify.com/static/sample-images/bath.jpeg",
//   operations: {
//     width: 800,
//     height: 600,
//     crop: "center"
//   }
// }

You can bypass auto-detection by specifying the provider:

const url = transformUrl(
	"https://cdn.shopify.com/static/sample-images/bath_grande_crop_center.jpeg",
	{
		width: 800,
		height: 600,
		provider: "shopify",
	},
);

This is particularly useful if you are using the CDN with a custom domain which is not auto-detected.

You can also specify a fallback provider to use if the URL is not recognised as coming from a known CDN:

const url = transformUrl(
	"https://example.com/image.jpg",
	{
		width: 800,
		height: 600,
		fallback: "netlify",
	},
);

This is useful if you are using a CDN provider that supports external images, but you still want to use the original CDN if possible.

Custom operations

Different CDNs support different operations. By default, the transform function accepts the operations width, height, quality and format. You can pass provider-specific operations as the third argument to the transformUrl function:

const url = transformUrl(
	"https://cdn.shopify.com/static/sample-images/bath.jpeg",
	{
		width: 800,
		height: 600,
	},
	{
		shopify: {
			crop: "center",
		},
	},
);

You can pass options for multiple providers, which will be passed to the provider depending on the detected CDN:

const url = transformUrl(
	src,
	{
		width: 800,
		height: 600,
	},
	{
		shopify: {
			crop: "left",
		},
		imgix: {
			position: "left",
		},
	},
);

These options are type-safe, as we include the types for each provider.

You can do the same for provider options, such as base URLs project keys.

const url = transformUrl(
	src,
	{
		width: 800,
		height: 600,
		fallback: "cloudinary",
	},
	{
		shopify: {
			crop: "left",
		},
	},
	{
		cloudinary: {
			cloudName: "demo",
		},
	},
);

Provider imports

If you know which providers you will be using, you can import them directly. This will reduce the bundle size of your application, as only the providers you use will be included. In this case you can pass provider-specific operations in the object.

import { transform } from "unpic/providers/shopify";

const url = transform(
	"https://cdn.shopify.com/static/sample-images/bath.jpeg",
	{
		width: 800,
		height: 600,
		crop: "center",
	},
);

Supported Providers

• Adobe Dynamic Media (Scene7)
• Builder.io
• Bunny.net, including caisy
• Cloudflare
• Contentful
• Contentstack
• Cloudinary
• Directus
• ImageEngine
• Imgix, including Unsplash, DatoCMS, Sanity and Prismic
• Kontent.ai
• Shopify
• Storyblok
• Supabase
• Vercel / Next.js
• WordPress.com and Jetpack Site Accelerator

FAQs

• What is an image CDN? An image CDN is a service that provides a URL API for transforming images. This is often used to resize images on the fly, but can also be used to apply other transforms such as cropping, rotation, compression, etc. This includes dedicated image CDNs such as Imgix and Cloudinary, CMSs such as Contentful, Builder.io and Sanity, general CDNs such as Bunny.net that provide an image API, but also other service providers such as Shopify. The CMSs and other service providers often use a dedicated image CDN to provide the image API, most commonly Imgix. In most cases they support the same API, but in others they may proxy the image through their own CDN, or use a different API.

• Why would I use this instead of the CDN's own SDK? If you you know that your images will all come from one CDN, then you probably should use the CDN's own SDK. This library is designed to work with images from multiple CDNs, and to work with images that may or may not be from a CDN. It is particularly useful for images that may come from an arbitrary source, such as a CMS. It is also useful for parsing URLs that may already have transforms applied, because most CDN SDKs will not parse these URLs correctly.

• Can you add support for CDN X? If it supports a URL API and doesn't require signed URLs then yes, please open an issue or PR.

• Can you add my domain to CDN X? If you provide a service where end-users use your URLs then probably. Examples may be image providers such as Unsplash, or CMSs. If it is just your own site then probably not. You can manually specify the provider in the arguments to transformUrl and parseUrl.

• What params can I use? The library provides a standard set of operations (width, height, format, quality) that work across all providers. You can also use provider-specific operations by passing them as the third argument to transformUrl. These are fully type-safe - your IDE will show you which operations are available for each provider.

• Why do you set auto format? If the CDN support is, and no format is specified in transformUrl, the library will remove any format set in the source image, changing it to auto-format. In most cases, this is what you want. Almost all browsers now support modern formats such as WebP, and setting auto-format will allow the CDN to serve the best format for the browser. If you want to force a specific format, you can set it in transformUrl.

• Why do you set fit=cover (or equivalent)? If the CDN supports it, and no fit is specified in transformUrl, the library will set fit to cover. This is because in most cases you want the image to fill the space, rather than be contained within it. Every CDN has its own syntax for this, so it's best if we set a default that applies to all images. If you want to force a specific fit, you can set it in transformUrl.

• Do you support SVG, animated GIF etc? If the CDN supports it, then yes. We don't attempt to check if a format is valid - we will just pass it through to the CDN. If the CDN doesn't support it, then it will return an error or a default.

• Do you support video, etc? No, this library is only for images. If you pass a video URL to transformUrl, it will return undefined, as it will for any URL that is not recognised as an image CDN URL. It is up to you to handle this case.

Contributing

See the contributing guide.