Image 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. It works with the module Iiif Server, that provides main manifests for items.
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 Image 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 Image 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.
The IIIF manifests can be displayed with many viewers, the integrated OpenSeadragon, the Universal Viewer, the advanced Mirador, or the ligher and themable Diva, or any other IIIF compatible viewer.
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.
The module Iiif Server is currently required and should be installed first.
Note: To keep old options from Universal Viewer, upgrade it to version 3.4.3 before enabling of ImageServer. Else, simply set them in the config form.
- From the zip
Download the last release ImageServer.zip from the list of releases (the
master does not contain the dependencies), uncompress it in the modules
directory, and rename the module folder ImageServer.
- 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 ImageServer, 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 Image 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 apache2Then, 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>.
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).
All routes of the Image 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-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.
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.
In case of big files, it is recommended to use the command line version of ImageMagick, that is not limited by the php memory.
Furthermore, the limit of the size (10000000 bytes by default) can be increased if you have enough memory, so images won't appear blurry even if they are not tiled.
-
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).
The tiles can be created in bulk via a job, that can be run via a button in the config form of the module.
-
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.
- Create thumbnails from the tiled image, not from the original.
- Support curl when allow_url_fopen and allow_url_include are forbidden.
- Automatically manage pdf as a list of canvas and images (extract size and page number, then manage it by the image server)
- Support a different route for iiif version 2 and iiif version 3, plus the default one.
See module Iiif Server.
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.
See online issues on the module issues page on GitHub.
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.
- Copyright Daniel Berthereau, 2015-2020 (see Daniel-KM)
- Copyright BibLibre, 2016-2017
First version of this plugin was built for the Bibliothèque patrimoniale of Mines ParisTech.