It is important to address the issue of who will archive digital image files. Another basic decision is what kinds of files will be archived, how the archive will be protected from format obsolescence and media failure, and what kind of metadata scheme will be used to facilitate searches.
Without careful filing, it can be hard to find a specific image. However, most image file formats (including all of those that we recommend here) include space for metadata that facilitate cataloging and searching with a digital asset management programs (such as Extensis Portfolio or iView MediaPro). Embedding IPTC metadata in image files early in a workflow, paired with logical file numbering and naming conventions, speeds up cataloging and facilitates searching.
Storing multiple copies of image files on redundant hard drives is arguably the most convenient and least expensive solution to guard against data loss. Additional back-ups to CD-R or DVD-R media may be prudent. Note, however, that different brands and batches of CD-R and DVD-R media have different archival qualities. Use only media with high archival ratings; burn discs at lower speeds; do not use adhesive labels on discs; and write on discs only with non-solvent markers designed specifically for inscribing CDs and DVDs, writing only on the hub of the disc.
A prudent practice is to maintain a complete copy of your photo archive off-site. However, be aware of one potential problem with any type of online copy: If there is corruption in your primary copy and you have your system set to automatically clone it to the backup, you can corrupt the backup.
Over time, as operating systems change and new storage media emerge, it will likely be necessary to migrate your digital image files. Most businesses and institutions have been slow to recognize the need for digital asset management, so it generally falls to photographers to maintain digital image archives. It’s wise to discuss archiving responsibilities with clients to avoid losing image files.
Archiving RAW image files from Digital SLR cameras is likely be a key challenge in the long-term maintenance of a digital archive. Because each camera model creates a unique file type, the likelihood of files becoming unreadable at some time in the future is high. Photographers should develop a comprehensive strategy to confront this issue, accounting for the probable obsolescence of file formats and the necessity for file format migration.
File format migration refers to the practice of conversing image files to a different (newer) storage format. This can come in the form of conversion to TIFF files, conversion to DNG files, or conversion to some future format not even in existence today. Each of these choices holds certain advantages and disadvantages regarding image quality, storage needs, and workflow requirements. Some of these concerns are outlined below.
Conversion to TIFF files: By converting images to TIFF format, the photographer is storing the images in the most accessible file format. Because TIFF is an open standard, it is likely to be readable for a very long time. TIFF also offers a workflow advantage: By converting to TIFF, you probably eliminate the need to reconvert the files again for many years, perhaps even for your lifetime. So images can be converted and archived with confidence that they are safely accessible long into the future.
There is a downside, however. TIFF files are much larger than RAW files. Converting image files to 16-bit TIFFs can make the files up to 10 times larger than RAW files and 15 times larger than compressed DNG. This will clearly increase the cost of file storage (assuming other costs stay the same). Although TIFF files have several compression options (LZW, ZIP, and JPEG), none of them are recommended due to the lack of universal support for a compressed TIFF format. This is especially important if you do not know exactly who will be receiving the file. Another downside to conversion to TIFF is that it precludes the use of better RAW converters that are surely coming in the future. Just as Photoshop CS3 does a better conversion than Photoshop CS2 does, it is likely that the RAW file conversion programs we will have several years from now will do an even better job than our current tools.
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.
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. As conversion software improves, new versions of the file can be made that will can have better color fidelity, or better noise reduction, or better upsizing interpolation. By keeping the RAW file intact, the largest number of future conversion options is preserved.
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. This may involve the conversion and re-cataloging of hundreds of thousands of image files. If this conversion is not accomplished before that particular format becomes generally unreadable, then the conversion may simply never happen, and those images may be lost. Additionally, since RAW files are proprietary, it is not a safe practice to alter these files. This means that any work you do to these files, such as the addition of metadata or tonal adjustments to the image, should not be stored in the file itself. This is typically accomplished by the use of either “sidecar” files or the storage of these adjustments in some kind of larger database. The splitting of this information makes for a file-management challenge that may present a serious roadblock in the future, as you try to include this work in a conversion file. Although some software can add metadata to RAW files, there can be conflicts with Adobe Bridge not reading the processing information in the XMP file after metadata has been added to the file by another program. You should always test for anomalies before adding metadata to proprietary RAW files.
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. Because of this, cataloging applications like iVIew MediaPro and Extensis Portfolio can see metadata that has been entered in Photoshop, and these programs can see the image adjustments made in Photoshop. DNG files can be re-opened in Photoshop as though they were RAW files, and offer the full range of conversion options in Photoshop that the original RAW file offered.
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. Additionally, DNG offers significant file-size savings through a lossless compression that can reduce the file size by up to one third. DNG also offers the possibility of embedding the RAW file itself, so that it can be re-converted later if desired. Of course, this particular option makes the DNG almost double the size of the original RAW file, so it isn't always to be recommended.
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. Also, by converting a RAW file to DNG, you currently preclude using the camera manufacturer’s software for converting this file. If you like the conversions you get from the manufacturer’s software more than the conversions you get from Photoshop, then DNG may be unacceptable.
The DNG converter attempts to copy “Undocumented Maker Notes” to the metadata of the DNG file. These maker notes might include information that could be useful in converting the file at a later date (such as “dust reference” information, or information helpful in correcting for chromatic aberration). By converting to DNG today, you may lose this data, since it is currently undocumented and it may not be copied correctly.
The archiving JPEG section is based on research and analysis by Ken Fleisher. This rest of this analysis of archival image formats was prepared by Peter Krogh. A more in-depth discussion of these issues, as well as all issues related to the creation and maintenance of a digital archive, can be found in his book, The DAM Book: Digital Asset Management for Photographers (O’Reilly, 2006). It’s available directly from the author, from O’Reilly, or from Amazon and similar distributors.