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https://github.com/samvera/node-iiif

This module provides a full-featured IIIF Image API 2.1 and 3.0 image processor. It covers only the image processing pipeline itself, leaving input and output to the caller.
https://github.com/samvera/node-iiif

iiif iiif-image nodejs

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

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# iiif-processor



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This module provides a full-featured image processor supporting the IIIF Image API versions [2.1](https://iiif.io/api/image/2.1/) and 

[3.0](https://iiif.io/api/image/3.0/). It covers only the image processing pipeline itself, leaving input and output to the caller.



## Install with NPM



```sh

npm install iiif-processor --save

```



## Usage



```javascript

const IIIF = require('iiif-processor');



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

```



* `url` (string, required) - the URL of the IIIF resource to process

* `streamResolver` (function, required) – a callback function that returns a readable image stream for a given request ([see below](#stream-resolver))

* `opts`:

  * `dimensionFunction` (function) – a callback function that returns the image dimensions for a given request ([see below](#dimension-function))

  * `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](#path-prefix))

  * `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](./examples/tiny-iiif/README.md) 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`)](#id--baseurl) and returns an open

[Readable Stream](https://nodejs.org/api/stream.html#stream_class_stream_readable) from which the source image can be read.



#### Pairtree File Source



```javascript

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



```javascript

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`)](#id--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.



```javascript

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 `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](https://www.w3schools.com/jsref/jsref_obj_regexp.asp). 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

```javascript

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

```javascript

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](#stream-resolver) and [dimensions function](#dimension-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](https://www.npmjs.com/package/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](https://samvera.atlassian.net/wiki/spaces/samvera/pages/405212316/Code+of+Conduct) and [language recommendations](https://github.com/samvera/maintenance/blob/main/templates/CONTRIBUTING.md#language).  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](LICENSE).