Wavelet Compression Technology
The sharp display of very large digital files with minimal loading time is made possible by wavelet technology. As of January 2005, the Library of Congress will be using two methods of wavelet compression to serve large images: MrSID and JPEG2000.
The key feature of both is their use of tiling to compress digitized images, which allows high compression with minimal loss of detail. Tiling also gives both MrSID and JPEG2000 the ability to decompress only that portion of an image requested by the user.
By allowing immediate access to any part of an image, of any size, at any resolution, MrSID and JPEG2000 are ideal for viewing the Library’s large documents (newspapers, rare books, manuscripts) and maps, which are up to 4 GB in size.
The Library has used MrSID (Multi-resolution Seamless Image Database) technology from LizardTech since 1996.
MrSID's compression ratio is approximately 22:1, depending on image content and color depth.
To download and view maps in the MrSID format you need a MrSID viewer. LizardTech has discontinued this viewer and no longer offers support on the product. The Library provides access to this viewer, but does not provide help or support for the product. Download the MrSID viewer.
The Library adopted the use of JPEG2000 (Joint Photographers Expert Group) file format in January 2005.
JPEG2000's compression ratio is approximately 20:1, depending on image content and color depth.
MrSID and JPEG2000 technology require no special software for viewing images online. For users who wish to download images, please visit our How to View page for software options.