Cool Things in Seadragon: World Digital Library

April 22, 2009

The World Digital Library is a collection of significant primary documents from countries and cultures around the world.  The folks over there have put them online (as of April 21st) to both promote cultural understanding as well as to provide a resource for educators and scholars.  They’ve also utilized Seadragon Ajax to do so, and the end product is really, really cool.

World Digital Library

Simply select a world region that you want to explore and you’ll be taken to a page containing all of your “search results” and a pane on the left to help you narrow down the items you have available to you.  Picking an individual item will give you a general description and all of the item’s particulars, such as creation date, author, location etc.  One more click on the item will send you into the Seadragon Ajax portion of the site, where you can zoom and pan around the item to your hearts content.  There’s a ton of interesting documents and photos to peruse here, so if you’re having a hard time choosing, start with a personal favorite of mine, the iconic photo of pea-pickers by Dorothea Lange.

The images do suffer from some pixel drift, though this is a product of using Kapil’s Python script for image conversion to DZI. It is also worth noting that this same gentleman did development on the WDL site.  They’ve also changed the Seadragon Ajax UI buttons, but that’s to incorporate a “next” and “previous” button for documents that have multiple pages.  It’s a wonderful site, and I suggest you check it out.

Kevin Hanes



  1. Kevin,

    WDL is really nice site, thanks for sharing.
    Could you please elaborate a bit more you what mean by pixel drift and what’s causing it exactly, as the Python Deep Zoom Tools I’ve developed are based on Kapil’s original script. I’d love to fix this, in case I happen to have the same issue with my script.


  2. When you replace a low res tile with a high res tile, you want the images on those tiles to match just right so it looks like the picture is just coming into focus. If they don’t match perfectly, it looks like the picture is moving as well as coming into focus. We call this effect pixel drift.

    Pixel drift can creep into the tiles that make up a DZI in a number of ways. Your level sizes could be off (for instance accumulated rounding errors), or your pixel interpolation algorithm may have some drift built in.

    For diagnosing pixel drift, it’s best to have a setup where you can scrub through the different levels that make up your image pyramid. This way the picture is locked down, and it’s obvious if your pixels are drifting.

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