samvera
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 --saveUsage
const IIIF = require('iiif-processor');
const processor = new IIIF.Processor(url, streamResolver, opts);url(string, required) - the URL of the IIIF resource to processstreamResolver(function, required) – a callback function that returns a readable image stream for a given request (see below)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 returnedwidth(integer) - the maximum pixel width of the returned imageheight(integer) - the maximum pixel height of the returned imagearea(integer) - the maximum total number of pixels in the returned image
includeMetadata(boolean) – iftrue, all metadata from the source image will be copied to the resultdebugBorder(boolean) – iftrue, 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 (2or3) 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 callback
function, which takes information about the request (id and baseUrl) and returns an open
Readable Stream from which the source image can be read.
Pairtree File Source
function streamResolver({ id, baseUrl }) {
let imagePath = '/path/to/image/root/' + id.match(/.{1,2}/g).join('/') + '/image.tif';
return fs.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
const { GetObjectCommand, S3Client } = require('@aws-sdk/client-s3');
async function streamResolver({ id, baseUrl }, callback) {
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}`);
}
try {
return callback ? await callback(stream) : stream;
} finally {
stream.destroy();
}
}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, baseUrl }) {
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
pathPrefixmust start and end with/. - The
pathPrefixmust include the{{version}}placeholder unless theversionconstructor option is specified. If both are present, the constructor option will take precedence. - To allow for maximum flexibility, the
pathPrefixis 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
const IIIF = require('iiif-processor');
let url = 'http://iiif.example.com/iiif/2/abcdefgh/full/400,/0/default.jpg'
let processor = new IIIF.Processor(url, streamResolver, { dimensionFunction });
processor.execute()
.then(result => handleResult(result))
.catch(err => handleError(err));Async/Await
const IIIF = require('iiif-processor');
let url = 'http://iiif.example.com/iiif/2/abcdefgh/full/400,/0/default.jpg'
let processor = new IIIF.Processor(url, streamResolver, { dimensionFunction });
try {
let result = await processor.execute();
return result;
} 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:
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.