For many years, libraries and archives have used the JPEG and TIFF coding standards to store images in an electronic format. These older standards were not designed to integrate the presentation of technical and descriptive metadata associated with images that has become so crucial to long-term usability, nor provide for quick access to these bundles of information. JPEG 2000, named by the Joint Photographic Experts Group, was created to offer these and other significant improvements over the first JPEG standard. In particular, the JPEG committee sought to create an open standard that provided the ability to bundle metadata with images in the same physical file, better efficiency in image compression including the option of âlosslessâ compression, and storage of multiple resolutions of the same image in one file. The intention of the committee is for JPEG 2000 to replace JPEG as the prevalent standard for storing digital images across many industries and research fields. Although members of the library and archives communities were not explicitly involved with the creation of the new standard, the characteristics of JPEG 2000 files are of great interest. JPEG 2000 is not only an evolutionary progression of formats but also as a revolutionary step that changes best practices in ways that can sustain the profession for a long period of time.
Best practices for the storage of digital images in the library and archives communities use the TIFF and JPEG file formats. The older JPEG format reduces the amount of space required to store images through a form of compression that sacrifices image detail. The TIFF format provides options for compression that do not affect image fidelity, but few have gained wide acceptance and those that have are based on patented algorithms. By comparison, the compression scheme used by JPEG 2000 is free of license and royalty restrictions and provides for âlosslessâ compression of image data.
An âopen standardâ is one that is free for anyone to read, understand, and implement with no royalties or fees. TIFF is an open standard, although the optional compression algorithm it uses is not. Another file format used extensively in the map and satellite photography fields, SID, offers compression but is also patented technology. The JPEG 2000 standard, as with all open standards, encourages multiple products for processing these files to be created in a competitive marketplace with assurance that adherence to the standard will result in interoperability. The open nature of the standard also ensures that software can be written to process the files long after a commercial advantage has been realized.
The growing abundance of preservation-quality images and their associated metadata is bringing into sharp relief the need to effectively manage these resources over the long term. To date, effort has been focused on building complex software systems that bind the metadata with the appropriate image file. JPEG 2000 introduces the concept of metadata bundles within the file format itself, permanently associating the metadata with the image in one digital object.
As an image file format, TIFF had its origins in the 1980s in desktop publishing and related industries. The practice and terminology from those fields carried forward to the library and archives communities as the format was adopted as standard practice. In the intervening quarter century, imaging technology evolved with a field of science called signal processing that, at its core, represents images as mathematical algorithms. In doing so, the imaging community became concerned with the introduction of ânoiseâ in the image âsignalâ from the hardware, software, and the process for capturing the image (e.g., misalignment of lenses, proper lighting of objects, and adequate construction of sensors). In order to get the most accurate reproduction of the original object in the signal, the noise needs to be reduced. To make the greatest use of JPEG 2000 as an image format, the professionals in our communities must advance their knowledge and understanding of digital image capture with concepts and language from the signal processing field.