JPEG2000 is a relatively new image file format, created by the JPEG Committee in 2000. JPEG2000, despite its name, is not a JPEG format, but utilises a clever compression technology that maximises quality while minimizing file sizes.
The Wellcome Library, anticipating a growth in digitisation of library materials as it takes forward an ambitious digitisation program, recognises the value of efficiency in storing its digital content whilst maintaining the high levels of quality and open standards required for long-term preservation. However, JPEG2000 comes in a variety of “flavours” and comprises 12 “parts”, as explained in the JPEG2000 specification.
Seeking to determine exactly which JPEG2000 format to use to meet the aims of long-term storage and accessible delivery services, the Library commissioned a report by Simon Tanner, Director of King’s Consultancy Service (KDCS). The report was written in conjunction with Robert Buckley of Xerox Corporation, an expert in the technical specifications of the JPEG2000 format.
As a result of the recommendations and conclusions provided in the report, the Wellcome Library will adopt a “visually lossless” lossy compression to gain at least 75% storage savings in comparison to a TIFF version (depending on the type of material being digitised). The recommended compression parameters will produce an image with no visible difference in image quality, but the compression is irreversible – i.e. the original bit stream will not be possible to reconstruct. As the Library will be digitising physical items that can (if necessary) be re-digitised, it was considered an acceptable compromise.
Embedding multiple resolution layers and tiling will facilitate dissemination, allowing a single image file to address multiple needs (such as thumbnails, screen resolution, and print resolution). In future, the Library will incorporate a web delivery system that can exploit these characteristics to create on-the-fly derivatives that can be viewed through a browser or downloaded (e.g. JPEG and PDF).
The full report is available under the Creative Commons Attribution Non-Commercial 2.0 license, and can be viewed and downloaded from the image viewer below (toggle full screen to read), or here.