On the ImageLib mailing list, Rob Lancefield (Manager of Museum Information Services for Wesleyan University) posted a link to the Universal Photographic Digital Imaging Guidelines (UPDIG) for image creators. The introduction says: "These 12 guidelines — provided as a Quick Guide plus an in-depth Complete Guide — aim to clarify the issues affecting accurate reproduction and management of digital image files. Although they largely reflect a photographer's perspective, anyone working with digital images should find them useful.... This document, prepared by the UPDIG working group, represents the industry consensus as of September 2007." The listed members of UPDIG leads one to believe that this is a professional photography group. One thing in the introduction to the guidelines caught my eye, though:
The chapter on archiving now has a discussion of JPEG as an archival format.
Note that the authors do indeed mean JPEG (circa 1994), not JPEG2000. The chapter on archiving lists the pros and cons of a number of formats, to include JPEG. The following bullet points are excerpted from the text.
- Conversion to TIFF files: By converting images to TIFF format [from camera RAW], the photographer is storing the images in the most accessible file format... There is a downside, however. TIFF files are much larger than RAW files... Another downside to conversion to TIFF is that it precludes the use of better RAW converters that are surely coming in the future.
- Archiving JPEG files: Conventional wisdom holds that the TIFF format holds a quality advantage over the JPEG format. This holds true only if the JPEG file is saved at less than 10 quality using the Photoshop standard. When using JPEG quality 10 or 12, the artifacts are either non-existent or insignificant. Higher bit-depth is really the only advantage of using TIFF over JPEG 10 or 12 (in terms of image quality)... Update 2008-02-11: Please see below.
- Archiving RAW files: If a photographer chooses to archive the RAW file, then he will be preserving the largest number of options for future conversion of the files... This, too, has its downside. RAW files will likely have to be converted to a more universal file format at some time in the future.
- Archiving DNG files: RAW files can be converted to DNG, a documented TIFF-based format created by Adobe that can store the RAW image data, metadata, and a color-corrected JPEG preview of the image. The DNG file format provides a common platform for information about the file and adjustments to the image... DNG is likely to be readable long after the original RAW format becomes obsolete, simply because there will be so many more of them than any particular RAW file format... There’s a downside to DNG, of course. Conversion to DNG requires an extra step at the time of RAW file processing; it does not take terribly long, but it is an extra process.
Update 2008-02-11: Ken Fleisher noted in the comments that the excerpt above was truncated before his reasoning was described. In the interest of clarity, the full text of this bullet point on the UPDIG site is:
Archiving JPEG files: Conventional wisdom holds that the TIFF format holds a quality advantage over the JPEG format. This holds true only if the JPEG file is saved at less than 10 quality using the Photoshop standard. When using JPEG quality 10 or 12, the artifacts are either non-existent or insignificant. Higher bit-depth is really the only advantage of using TIFF over JPEG 10 or 12 (in terms of image quality). Some have argued that that JPEG, because of the way it encodes data, compromises color. This is a misconception. When using the highest quality settings, there is no loss of color fidelity. Therefore, if JPEG files are saved at 10-12 quality, and if they do not require much pixel editing before use, archiving JPEG files is not a bad concept, and it can save a lot of space. For many picture archives, the economics of storing large numbers of files dominates all other considerations, and JPEG offers a feasible solution to the problem.
The notes at the end of the chapter say: "The archiving JPEG section is based on research and analysis by Ken Fleisher."
So I wonder what is going on here. Does the cultural heritage community have a different definition of the word archive from the professional photography community? Are there sufficient differences in our goals that warrant the differences in practices?
This topic is of interest because the program of the Library and Information Technology Association (LITA) will be holding a panel at the on using the JPEG2000 file format for archival purposes. Part of the discussion will center around the notion of visually lossless versus data lossless compression. This mention of lossy-yet-high-quality JPEG compression seems to fit into the same topic.of the