iiif-processor

This module provides a full-featured image processor supporting the IIIF Image API versions 2.1 and 3.0. It covers only the image processing pipeline itself, leaving input and output to the caller.

Install with NPM

npm install iiif-processor --save

Usage

import { Processor } from "iiif-processor";

const processor = new Processor(url, streamResolver, opts);

• url (string, required) - the URL of the IIIF resource to process
• streamResolver (async function, required) – returns a Promise of a readable image stream for a given request (see below); the legacy two-argument callback form is deprecated
• opts:
  • dimensionFunction (function) – a callback function that returns the image dimensions for a given request (see below)
  • max (object) – optional maximum size constraints of an image that can be returned
    • width (integer) - the maximum pixel width of the returned image
    • height (integer) - the maximum pixel height of the returned image
    • area (integer) - the maximum total number of pixels in the returned image
  • includeMetadata (boolean) – if true, all metadata from the source image will be copied to the result
  • debugBorder (boolean) – if true, add a 1px red border to every generated image (for tile debugging)
  • density (integer) – the pixel density to be included in the result image in pixels per inch
    • This has no effect whatsoever on the size of the image that gets returned; it's simply for convenience when using the resulting image in software that calculates a default print size based on the height, width, and density
  • pageThreshold (integer) – the fudge factor (in number of pixels) to mitigate rounding errors in pyramid page selection (default: 1)
  • pathPrefix (string) – the template used to extract the IIIF version and API parameters from the URL path (default: /iiif/{{version}}/) (see below)
  • version (number) – the major version (2 or 3) of the IIIF Image API to use (default: inferred from /iiif/{version}/)

Examples

Full Self-Contained Application

See the TinyIIIF example.

Stream Resolver

The calling function must supply the processor with a Stream Resolver that returns a Promise of an open Readable Stream. It receives information about the request (id and baseUrl).

Pairtree File Source

async function streamResolver({ id, baseUrl }) {
  let imagePath = "/path/to/image/root/" + id.match(/.{1,2}/g).join("/") + "/image.tif";
  return createReadStream(imagePath);
}

The Stream Resolver can also take an async callback as its second parameter, in which case it should return the value of applying the callback to the stream. This allows the function to do its own cleanup.

Amazon S3 Bucket Source

import { GetObjectCommand, S3Client } from "@aws-sdk/client-s3";

async function streamResolver({ id, baseUrl }) {
  const s3 = new S3Client();
  const command = new GetObjectCommand({
    Bucket: "my-tiff-bucket",
    Key: `${id}.tif`
  });
  const response = await s3.send(command);
  const body = response.Body;

  if (!stream) {
    throw new Error(`Could not fetch object from S3: ${id}`);
  }

  return stream;
}

Note: The two-argument callback form is still supported but deprecated; prefer the promise-based resolver shown above. If you currently return a stream synchronously, wrap it with Promise.resolve() or mark your function async.

Dimension Function

The calling function can also supply the processor with an optional Dimension callback that takes information about the request (id and baseUrl) and returns the dimensions of the source image. This allows for caching dimensions and avoiding an expensive image request.

The function should return either:

• a {width: w, height: h} object indicating the dimensions of the source image
• an array of {width: w, height: h} objects indicating the dimensions of all of the pages available within the source image, if it is a multi-resolution image (e.g., a pyramidal TIFF), e.g.:

  [
    { width: 14499, height: 12069 },
    { width: 7249, height: 6034 },
    { width: 3624, height: 3017 },
    { width: 1812, height: 1508 },
    { width: 906, height: 754 },
    { width: 453, height: 377 },
    { width: 226, height: 188 }
  ]
  

Providing the dimensions of all available pages allows the processor to choose the most efficient starting image for the size requested.

async function dimensionFunction({ id: string, baseUrl: string }): Promise<Dimensions | Dimensions[]> {
  let dimensions = lookDimensionsUpInDatabase(id);
  return { width: dimensions.width, height: dimensions.height };
}

Path Prefix

The pathPrefix constructor option provides a tremendous amount of flexibility in how IIIF URLs are structured. The prefix includes one placeholder {{version}}, indicating the major version of the IIIF Image API to use when interpreting the rest of the path.

• The pathPrefix must start and end with /.
• The pathPrefix must include the {{version}} placeholder unless the version constructor option is specified. If both are present, the constructor option will take precedence.
• To allow for maximum flexibility, the pathPrefix is interpreted as a JavaScript regular expression. For example, /.+?/iiif/{{version}}/ would allow your path to have arbitrary path elements before /iiif/. Be careful when including greedy quantifiers (e.g., + as opposed to +?), as they may produce unexpected results. / characters are treated as literal path separators, not regular expression delimiters as they would be in JavaScript code.

Processing

Promise

import { Processor } from "iiif-processor";

let url = "http://iiif.example.com/iiif/2/abcdefgh/full/400,/0/default.jpg"
let processor = new Processor(url, streamResolver, { dimensionFunction });
processor.execute()
  .then(result => handleResult(result))
  .catch(err => handleError(err));

Async/Await

import { Processor } from "iiif-processor";

let url = "http://iiif.example.com/iiif/2/abcdefgh/full/400,/0/default.jpg"
let processor = new Processor(url, streamResolver, { dimensionFunction });
try {
  return await processor.execute();
} catch (err) {
  handleError(err);
}

id / baseUrl

The stream resolver and dimensions function functions both accept an object with id and baseUrl specified.

For instance, for the request:

https://example.org/iiif/assets/42562145-0998-4b67-bab0-6028328f8319.png/10,20,30,40/pct:50/45/default.png

The id parameter is 42562145-0998-4b67-bab0-6028328f8319.png and the baseUrl is https://example.org/iiif/assets.

Contributing

Contributions are welcome in the form of bug reports, suggestions, pull requests, and/or documentation.

If you're working on a PR for this project, create a feature branch off of main.

This project uses the debug library for selective debugging output. To view all IIIF-related debug messages, set the environment variable DEBUG=iiif-processor:*. To view just the main or transformer contexts, set DEBUG=iiif-processor:main or DEBUG=iiif-processor:transform.

This repository follows the Samvera Community Code of Conduct and language recommendations. Please do not create a branch called master for this repository or as part of your pull request; the branch will either need to be removed or renamed before it can be considered for inclusion in the code base and history of this repository.

License

node-iiif is available under the Apache 2.0 license.