Veridian’s Diary - Low resolution image pre-generation for Veridian viewer

Our clients and indeed any users of a Veridian digital collection will be familiar with the image viewer, so for this Veridian’s Diary entry we’d like to share an improvement we’ve recently made to this tool.

If you’re not acquainted with how our image server works, rather than follow the pre-generated image approach used by other platforms such as Olive/Ignite and CONTENTdm, the Veridian image server generates images on demand as users browse collections.

The advantages of this approach include the ability to display images in different dimensions, resolutions and formats, and ensure the displayed images are always up-to-date - even if the source documents are replaced. This method also avoids some of the disadvantages that come with using pre-generated images, including limitations on the image formats available, and as most of our collections contain either hundreds, thousands or millions of pages, pre-generated images significantly increase server disk usage requirements.

However, generating images on demand is not without its own drawbacks. This approach requires more processing power, and there is often a few seconds of wait time before the images are generated, regardless of how powerful the server is. In some cases, this can lead to a disjointed user experience.

In order to directly address this initial wait time, we’ve developed a hybrid approach for the Veridian viewer that sits between image generation on demand and pre-generation, to move closer to a ‘best of both worlds’ situation. The latest version of Veridian allows collections to pre-generate only the lower resolution page-level images, so when users visit a document the low resolution page images load immediately. This means we have significantly reduced the potential wait time before the first image appears. Additionally, when users navigate through the document subsequent pages will also be visible faster.

The pre-generated low resolution images require ~2.5GB of space per 100,000 pages in the collection, depending on the size of the original images. This new feature is optional and can be turned on for a Veridian digital collection by request. We already have two collections with this feature enabled, the Catholic News Archive and Papers of Princeton.