Deep Zoom and others for displaying large images on the web

Slashgeo have noted the release of Deep Zoom in Javascript aka Seadragon, by Microsoft. Deep Zoom allows one to deliver a very high resolution image over the web, with pan and zoom. Only the portions viewed are download, so bandwidth usage is minimised. Until now Deep Zoom was Silverlight only. It works similarly to OpenStreetMap, Google Maps or Live Search Maps. A large image is transformed into a ‘pyramid’, by generating lower resolution versions (e.g. full, ½, ¼, …) and stacking them until a peak is reached. Each level is cut into square tiles, which are stored individually in a known hierarchy. The pyramid generation is similar to mip-mapping. The image might be satellite or aerial photography, a scanned map, a legal document, medical imagery (e.g. a smear test or x-ray) or any highly detailed photograph. Deep Zoom joins a collection of platforms and technologies that perform a similar role, which I’ll briefly summarise.

IIPImage

IIPImage is an Open Source package that has a similar design to Deep Zoom, it’s named after the Internet Image Protocol. The tiles are extracted as needed from a specially constructed tiff file. On the server a FastCGI module extracts the tiles as needed. Clients written in Java (demo), Flash (demo) and AJAX (demo) clients are available.

Lizardtech GeoExpress/MrSID

Lizardtech ExpressView is a browser plugin to view files in the proprietary MrSID image format. MrSID files can achieve higher compression ratios than JPEG for a given image quality, particularly for aerial imagery. ExpressView is Windows only, but is also able to render a MrSID file from a local disk or an email attachment. Encoding can be done with GeoExpress, or GDAL or other applications that embed the SDK.

OpenLayers

OpenLayers is a JavaScript library used for embedding a map (e.g. OpenStreetMap) within the browser. OpenLayers is not restricted to maps, it can be used with TileCache, to view any bitmap.

Zoomify

Zoomify is a long term player in this field, offering Zoomify EZ, Zoomify Flash and Zoomify Enterprise. The Flash client is free to use in it’s most basic form, or additional features are available for a fee.

Other image formats

JPEG 2000 is a open format similar in design to MrSID, but it has gained little traction on the desktop. HD Photo (aka JPEG XR, fka Windows Media Photo) is a fledgling format with similar capabilities to JPEG 2000 or MrSID, but cheaper encoding routines that make it faster to compress. ER Mapper ECW is again similar to MrSID and JPEG 2000, a Windows only ER Viewer is available. If you know of other formats, technologies or techniques, or if you’d like to know more, please leave a comment.