Changing Fallback Thumbnails

Omeka displays thumbnails for files in many places. However, useful thumbnails can’t be generated for all types of files, and for some files that could have a thumbnail, the server simply doesn’t have the libraries it needs to read that type of file and create the thumbnail.

In these situations, there is no thumbnail generated, so Omeka will use a fallback thumbnail instead. All Omeka 2 versions have images/fallback-file.png, a simple image of a blank page used to represent files generically. Omeka 2.2 adds more specific fallbacks for audio, video and image files.

Overriding thumbnails in themes

The fallback thumbnails are simply theme assets, so they can be overridden by a theme just including its own image in the same location. The default fallbacks are located in application/views/scripts/images and are PNG images with names starting with fallback-. fallback-file.png is present in all Omeka versions, and Omeka 2.2 adds fallback-audio.png, fallback-video.png and fallback-image.png.

In a theme, you can just put your own versions of those files in the theme’s images folder. The default images are 200x200 pixel square PNGs.

Adding new fallback thumbnails

In addition to just overriding the existing thumbnails, you can also add new fallbacks with a plugin.

The function add_file_fallback_image is used to add a new fallback image for a given MIME type or type family. The first argument is the MIME type the fallback will apply to, and the second is the name of the image to use. The image name is internally passed to img. The plugin should place the actual fallback image in its views/shared/images folder.

The fallback will only be used for files lacking thumbnails that match the MIME type (or family) you pass. The “family” is the part of the MIME type before the slash, “image” for “image/jpeg” for example.

The call to add_file_fallback_image should be made in the plugin’s initialize hook.