IIIF Server (module for Omeka S)

IIIF Server is a module for Omeka S that integrates the IIIF specifications and a simple image server (similar to a basic IIP Image) to allow to process and share instantly images of any size and medias (pdf, audio, video, 3D...) in the desired formats.

The full specifications of the International Image Interoperability Framework standard are supported (level 2), so any widget that supports it can use it. Rotation, zoom, inside search, etc. may be managed too. Dynamic lists of records may be created, for example for browse pages.

Images are automatically tiled to the Deep Zoom or to the Zoomify formats. They can be displayed directly in any viewer that support thes formats, or in any viewer that supports the IIIF protocol. Tiled images are displayed with OpenSeadragon, the default viewer integrated in Omeka S.

The IIIF Server supports the IXIF media extension too, so manifests can be served for any type of file. For non-images files, it is recommended to use a specific viewer or the Universal Viewer, a widget that can display books, images, maps, audio, movies, pdf, 3D, and anything else as long as the appropriate extension is installed.

This Omeka S module is a rewrite of the Universal Viewer plugin for Omeka by BibLibre with the same features as the original plugin, but separated into two modules (the IIIF server and the widget Universal Viewer). It integrates the tiler Zoomify that was used the plugin OpenLayers Zoom for Omeka Classic and another tiler to support the Deep Zoom Image tile format.

Installation

PHP should be installed with the extension exif in order to get the size of images. This is the case for all major distributions and providers. At least one of the php extensions [GD] or [Imagick] are recommended. They are installed by default in most servers. If not, the image server will use the command line ImageMagick tool convert.

• From the zip

Download the last release IiifServer.zip from the list of releases (the master does not contain the dependencies), uncompress it in the modules directory, and rename the module folder IiifServer.

• From the source and for development:

If the module was installed from the source, check if the name of the folder of the module is IiifServer, go to the root of the module, and run either:

    composer install

Then install it like any other Omeka module.

• CORS (Cross-Origin Resource Sharing)

To be able to share manifests and contents with other IIIF servers, the server should allow CORS. The header is automatically set for manifests, but you may have to allow access for files via the config of the server.

On Apache 2.4, the module "headers" should be enabled:

a2enmod headers
systemctl restart apache2

Then, you have to add the following rules, adapted to your needs, to the file .htaccess at the root of Omeka S or in the main config of the server:

# CORS access for some files.
<IfModule mod_headers.c>
    <FilesMatch "\.json$">
        Header add Access-Control-Allow-Origin "*"
        Header add Access-Control-Allow-Headers "origin, x-requested-with, content-type"
        Header add Access-Control-Allow-Methods "GET, POST, OPTIONS"
    </FilesMatch>
</IfModule>

It is recommended to use the main config of the server, for example with the directive <Directory>.

Notes

Note: To keep old options from Universal Viewer, upgrade it to version 3.4.3 before enabling of IiifServer. Else, simply set them in the config form.

When you need to display big images (bigger than 10 to 50 MB according to your server), it is recommended to upload them as "Tile", so tiles will be automatically created (see below).

Options for the IIIF server can be changed in the helpers "IiifCollection.php", "IiifManifest.php" and "IiifInfo.php" of the module, and via the events.

See below the notes for more info.

• Using externally supplied IIIF manifest and images

If you are harvesting data (via OAI-PMH, for instance) from another system where images are hosted and exposed via IIIF, you can use a configurable metadata field to supply the manifest to the Universal Viewer. In this case, no images are hosted in the Omeka record, but one of the metadata fields has the URL of the manifest hosted on another server.

For example, you could set the alternative manifest element to "Dublin Core:Has Format" in the module configuration, and then put a URL like "https://example.com/iiif/HI-SK20161207-0009/manifest" in the specified element of a record. The Universal Viewer included on that record’s display page will use that manifest URL to retrieve images and metadata for the viewer.

• Filtering data of manifests [TODO]

The module creates manifests with all the metadata of each record. The event uv.manifest can be used to modify the exposed data of a manifest for items and collections. For example, it is possible to modify the citation, to remove some metadata or to change the thumbnail.

IIIF Server

All routes of the IIIF server are defined in config/module.config.php. They follow the recommandations of the IIIF specifications.

To view the json-ld manifests created for each resources of Omeka S, simply try these urls (replace :id by a true id):

• https://example.org/iiif/collection/:id for item sets;
• https://example.org/iiif/collection/:id,:id,:id,:id... for multiple resources;
• https://example.org/iiif/:id/manifest for items;
• https://example.org/iiif-img/:id/info.json for images files;
• https://example.org/iiif-img/:id/:region/:size/:rotation/:quality.:format for images, for example: https://example.org/iiif-img/1/full/full/270/gray.png;
• https://example.org/ixif-media/:id/info.json for other files;
• https://example.org/ixif-media/:id.:format for the files.

By default, ids are the internal ids of Omeka S, but it is recommended to use your own single and permanent identifiers that don’t depend on an internal pointer in a database. The term Dublin Core Identifier is designed for that and a record can have multiple single identifiers. There are many possibilities: named number like in a library or a museum, isbn for books, or random id like with ark, noid, doi, etc. They can be displayed in the public url with the modules Ark and/or Clean Url.

If item sets are organized hierarchically with the plugin Collection Tree, it will be used to build manifests for item sets.

Image Server

The image server has two roles.

• Dynamic creation of tiles and transformation

  The IIIF specifications allow to ask for any region of the original image, at any size, eventually with a rotation and a specified quality and formats. The image server creates them dynamically from the original image, from the Omeka thumbnails or from the tiles if any.

  It is recommended to use the php extensions GD or Imagick. The command line tool ImageMagick, default in Omeka, is supported, but slower. GD is generally a little quicker, but ImageMagick manages many more formats. An option allows to select the library to use according to your server and your documents or to let the module chooses automagically.

• Creation of tiles

  For big images that are not stored in a versatile format and cannot be processed dynamically quickly, it is recommended to pre-tile them to load and zoom them instantly. It can be done for any size of images. It may be recommended to manage at least the big images (more than 10 to 50 MB, according to your server and your public).

  Tiles can be created in two formats: Deep Zoom and Zoomify. Deep Zoom Image is a free proprietary format from Microsoft largely supported, and Zoomify is an old format that was largely supported by proprietary image softwares and free viewers, like the OpenLayers Zoom. They are manageable by the module Archive Repertory.

  The tiles are created via a background job from the media "Tile" (in item edit view).

Note about the display of tiled and simple images

When created, the tiles are displayed via their native format, so only viewers that support them can display them. OpenSeadragon, the viewer integrated by default in Omeka S, can display the formats Deep Zoom and Zoomify directly (from version 2.2.2), so it is quicker. The OpenLayers viewer support the two formats too. The mode ("iiif" of "native") and other OpenSeadragon settings can be changed when the renderer is called.

When the viewer doesn’t support a format, but the IIIF protocol, the image can be displayed through its IIIF url (https://example.org/iiif-img/:id). This can be done for any image, even if it is not tiled, because of the dynamic transformation of images.

To display an image with the IIIF protocol, set its url (https://example.org/iiif-img/:id/info.json) in an attached media of type "IIIF" or use it directly in your viewer. The id is the one of the media, not the item.

3D models

The creation of manifests for 3D models is fully supported by the widget and natively managed since the release 2.3 of Universal Viewer via the threejs library.

• Possible requirement

The module Archive Repertory must be installed when the json files that represent the 3D models use files that are identified by a basename and not a full url. This is generally the case, because the model contains an external image for texture. Like Omeka hashes filenames when it ingests files, the file can’t be retrieved by the Universal Viewer.

This module is not required when there is no external images or when these images are referenced in the json files with a full url.

To share the json with other IIIF servers, the server may need to allow CORS (see above).

• Example

  • Allow the extension json and the media type application/json in the global settings.
  • Install the module Archive Repertory.
  • Download (or add via urls) the next three files from the official examples:
    • http://files.universalviewer.io/manifests/foundobjects/thekiss/thumb.jpg
    • http://files.universalviewer.io/manifests/foundobjects/thekiss/thekiss.jpg
    • http://files.universalviewer.io/manifests/foundobjects/thekiss/thekiss.json
  • Add a new item with these three files, in this order, and the following metadata:
    • Title: The Kiss
    • Date: 2015-11-27
    • Description: Soap stone statuette of Rodin’s The Kiss. Found at Snooper’s Paradise in Brighton UK.
    • Rights: 3D model produced by Sophie Dixon
    • License (or Rights): by-nc-nd
  • Go to the public page of the item and watch it!

Important: When using Archive Repertory and when two files have the same base name (here "thekiss.jpg" and "thekiss.json"), the image, that is referenced inside the json, must be uploaded before the json. Furthermore, the name of the thumbnail must be thumb.jpg and it is recommended to upload it first.

Finally, note that 3D models are often heavy, so the user has to wait some seconds that the browser loads all files and prepares them to be displayed.

TODO / Bugs

• When a item set contains non image items, the left panel with the index is displayed only when the first item contains an image.
• Separate IIIF Server (creation of manifests and media infos) and image server (tiling and display compliant with iiif specifications).
• Create thumbnails from the tiled image, not from the original.
• Support curl when allow_url_fopen and allow_url_include are forbidden.

Warning

Use it at your own risk.

It’s always recommended to backup your files and your databases and to check your archives regularly so you can roll back if needed.

Troubleshooting

See online issues on the module issues page on GitHub.

License

This module is published under the CeCILL v2.1 licence, compatible with GNU/GPL and approved by FSF and OSI.

In consideration of access to the source code and the rights to copy, modify and redistribute granted by the license, users are provided only with a limited warranty and the software’s author, the holder of the economic rights, and the successive licensors only have limited liability.

In this respect, the risks associated with loading, using, modifying and/or developing or reproducing the software by the user are brought to the user’s attention, given its Free Software status, which may make it complicated to use, with the result that its use is reserved for developers and experienced professionals having in-depth computer knowledge. Users are therefore encouraged to load and test the suitability of the software as regards their requirements in conditions enabling the security of their systems and/or data to be ensured and, more generally, to use and operate it in the same conditions of security.

This Agreement may be freely reproduced and published, provided it is not altered, and that no provisions are either added or removed herefrom.

The module uses the Deepzoom library and Zoomify library, the first based on Deepzoom of Jeremy Buggs (license MIT) and the second of various authors (license GNU/GPL). See files inside the folder vendor for more information.

Contact

See documentation on the IIIF on its site.

Current maintainers of the plugin for Omeka 2 and the module for Omeka S:

• Daniel Berthereau (see Daniel-KM)

First version of this plugin was built for the Bibliothèque patrimoniale of Mines ParisTech.

Copyright

• Copyright Daniel Berthereau, 2015-2018
• Copyright BibLibre, 2016-2017