It’s common to talk about “raw files” as if they were a single standard like JPEG. But nearly every camera capable of storing the unprocessed data from its sensor on a memory card actually uses its manufacturer’s proprietary format, which may even be specific to that model. This may not seem much of a problem, as those cameras almost always include a CD with raw conversion software packed in the box. There are also third-party raw converters that are often better than what the camera manufacturer provides.

The babel of formats could cause real trouble sooner than you might think. Like other forms of computer technology, digital cameras are evanescent. In a mere five years, Canon’s D30— a revolutionary 3-megapixel DSLR introduced in 2001— was successively replaced with the D60, the 10D, the 20D, and the 30D (which was replaced with the 40D in 2007). That’s just one manufacturer’s lineage, and doesn’t even include Canon’s professional DSLRs or the Digital Rebel/300D lineage that split from the 10D. In 2005 Canon dropped support for the D30 in their Digital Photo Professional raw converter. Complaints from the many people who still use the D30 forced Canon to restore that support. But who’s to say they won’t drop it again (perhaps along with the D60 and 10D) in a future version?

Even if you’re wealthy enough to replace your camera regularly, the ghosts of cameras past will still linger in your library of raw files. You could save the raw conversion software that came with those cameras and reinstall it when necessary. But what if it’s not compatible with your new computer or operating system? The 64-bit version of Microsoft’s Vista operating system no longer runs 16-bit “legacy” software written for DOS or Windows 3.1. Apple’s current Intel-based machines use the Macintosh’s third distinct processor family. So it’s not merely conceivable but very likely that 20 years from now, computers capable of installing your old 32-bit Windows raw converters will be found only in museums.

Adobe is attempting to solve this problem with DNG (pronounced ding, but sometimes dingy or dinghy), the Digital NeGative format. DNG is a publicly-documented specification of a standard format for storing raw camera data. Adobe is actively “encouraging” camera manufacturers to abandon their proprietary formats and adopt DNG. Until that happens, they’re promoting DNG as an archival format for photographers. Adobe provides free software that can convert many proprietary formats into DNG. They have been regularly updating it as they add support for new cameras to Adobe Camera Raw, Photoshop’s raw converter. The DNG converter can optionally embed the original raw files into DNG files to assure that nothing is lost.

It’s too early to tell whether DNG will actually provide a long-term solution to raw-file obsolescence. If any company has the market clout to convince (or bully) camera manufacturers into adopting a standard, it’s Adobe— unless Microsoft decides to enter that arena with a proprietary rights-managed format tied to Windows. But if DNG fails to reach critical mass, it could disappear a lot faster than the formats it’s meant to replace.

A few high-end (Hasselblad, Leica) and minor (Ricoh, Samsung) camera manufacturers have already adopted DNG, possibly with some “assistance” from Adobe. Coming late to the digital table, they stand to benefit the most from using a standard rather than developing their own raw formats. Whether the major players adopt it may depend on their marketing strategy. Canon currently gives away their Digital Photo Professional software to anyone who buys their cameras, so they would seem to have little to lose from adopting a standard. But Nikon sells their advanced Nikon Capture raw converter as an extra-cost accessory (their cameras come with the snapshooter-oriented Picture Project software, which provides rudimentary raw conversion). They would seem to have no incentive to give up their proprietary format and the revenue it provides.

Nikon received many complaints when they released new digital SLRs in 2005 that encrypted the white balance information in their raw files. Nikon issued a defiant press release defending the encryption as essential for the “preservation of [Nikon’s] unique technology.” In response, a “working group of photographers” formed OpenRaw, which promotes making complete documentation available for past, present, and future proprietary raw file formats. They carefully distinguish this initiative from Adobe’s goal of a common standard, which they consider impractical. Regardless, Nikon’s avaricious encryption of a minor part of their raw files may have paradoxically increased the demand among photographers for open access to those files. But it’s too early to say which approach (if any) will prevail.

A cynic might suspect that Adobe has an ulterior motive behind their apparent altruism in developing and promoting a “public” standard. Adobe Camera Raw is probably the most popular third-party raw conversion software, by virtue of its inclusion in Photoshop, Elements, and Lightroom. Version 4.4.1 (released in April 2008) supports 179 different cameras. Later updates will add more. That means Adobe must incur significant expense continually reverse-engineering or licensing all those proprietary formats. A single open standard would make things so much easier for them. Yes, it would also make things easier for other developers of third-party raw converters, but that’s not a problem. Adobe can just buy out any competitors that have a promising or threatening product, as they did with Pixmantec and RawShooter. The other benefits, including protecting photographers from obsolescence, are merely selling points. Although Adobe calls the DNG specification “public,” they have patented it. But they generously grant a free license to anyone who wants to develop software or hardware that uses DNG files; it’s the same arrangement they’ve made for their “public” but patented PDF format.

Cynicism aside, DNG is a promising technology that could have genuine benefits for photographers— if it ever catches on. It’s hard to make a recommendation about whether it’s worth using now as an archival format. I don’t use it, but my Canon Digital Rebel XT is a very popular camera that Canon (and Adobe Camera Raw) is likely to support for the foreseeable future. I would consider DNG if I had a collection of raw files from a camera whose manufacturer has gone bankrupt or has left the market (e.g., Konica-Minolta), or whose manufacturer that seems likely to leave the market due to an insignificant market share (e.g., Sigma). It might be more sensible to save the best output of your favorite raw converter as an uncompressed 16-bit TIFF file and/or a 16-bit flat PSD (native Photoshop) file (see A Bestiary of File Formats for more information). Both formats have enormous user bases and enough history to ensure that support will remain available for any foreseeable future.

Following is a brief discussion and comparison of seven file formats for photography and graphics. Don’t look for a complete or scholarly treatise. It’s merely my take on what they’re for, where they come from, their future prospects, and particularly how I use them.

TIFF is the grand-daddy of image file formats, originating in the mid-1980s. Designed from the outset to be flexible and extensible, it has many mutually-incompatible variants for specialized uses ranging from fax machines to desktop publishing. But in its simplest form of a single 24-bit or 48-bit color image without compression, TIFF is probably the most durable, compatible, and widely supported of the current file formats that can store full image data. With the notable exception of Web browsers, nearly all software that displays or edits images can read it. That compatibility comes at the price of large file size: each pixel of a color image requires three (or possibly six) bytes. That makes it unattractive for Web use, which is why browsers don’t support it. Some software allows compression, but the resulting files aren’t much smaller and may be unreadable in other programs. The compression option in Photoshop CS2 and CS3 actually increases the size of 48-bit TIFF files!

TIFF can store the metadata that digital cameras and some image editing programs create to record date, time, exposure, color space, owner, copyright, and other information. It also accommodates multiple channels (e.g., “alpha” channels for storing selections in image editors, infrared cleaning data from scanners, and the usual red, blue, and green). Photoshop’s implementation can store layers, making TIFF nearly interchangeable with its native PSD format.

I use TIFF for storing full-resolution finished, non-sharpened “master” images. From them I make everything else: the smaller versions for this Web site, prints, and any other products purchasers might want to license. I believe these simple uncompressed TIFF files are very likely to remain supported in future software, which makes them suitable for “archival” storage of finished images. But I could be wrong about that.

JPEG (“jay-peg,” named for the Joint Photographic Experts Group that developed the standard for it in 1992) is ubiquitous on the Web and in digital cameras for full-color 24-bit photographs. Every graphical browser supports it, and nearly all software that displays or edits images can read it. It uses “lossy” compression that attains very compact file sizes by cleverly exploiting the quirks and limitations of human vision. It discards a significant amount of data that the human eye and brain won’t miss (but birds might, as they see in four colors somewhat different from the three we see). Most software and cameras that create JPEG files can vary the compression to balance quality against file size. Too much compression means smeared color, lost detail, and artifacts. JPEG is limited to 8 bits per channel. It can store metadata but not alpha channels or layers.

JPEG with low compression (“maximum” or “highest” quality) is a good choice for storing final versions of images that don’t require further editing. When viewed or printed, such files are essentially indistinguishable from much larger uncompressed or losslessly-compressed files. But the lossy compression means that repeatedly opening and re-writing a JPEG file degrades the image. It’s rather like the way photocopies of photocopies get increasingly fuzzy. The lost data may also limit and complicate adjustments in an image editor, which can be a problem with digital camera JPEG files.

Because JPEG is so pervasive, it’s another likely candidate for future-proof archival storage, subject to its inherent limitations. I use JPEG for the small images on this Web site, and for delivering high-resolution licensed images to purchasers by download or e-mail (delivery in other formats may require mailing a CD, as the file size could be too large for Internet delivery).

GIF (“gif[t]” or “jiff”) is nearly as old as TIFF. Every graphical browser supports it, and nearly all software that displays or edits images can read it. It keeps file sizes small through “lossless” compression— when you uncompress the data you get back exactly what you started with. GIF is not useful for photographs because it allows a maximum of 256 colors. But it is useful for text or drawings, since lossless compression doesn’t create the artifacts and smearing that JPEG often produces with sharp, high-contrast edges. GIF supports “transparency,” which means you can designate one of the 256 colors as “invisible” so the background shows through it. That way, lettering, logos, or other images can appear to “float” on the page regardless of the color or background. I use GIF files (with transparent backgrounds) for the graphical titles at the top of the Travel Photo Essay pages on this Web site. Another common use of GIF is for animated images, since the GIF standard allows multiple images in a single file that Web browsers can display in rapid succession.

PNG (“ping”) was meant to replace GIF. CompuServe developed GIF in 1987, unaware that Unisys owned a patent on the “LZW” algorithm chosen for its lossless compression. Unisys slept while GIF became popular, first on computer bulletin boards and then on the nascent Web. In 1994 they woke up and put their lawyers to work, ordering developers of commercial software that creates GIF files to start paying royalties. Five years later, perhaps out of a greedy desire to squeeze everything they could out of their patent before it expired in 2003, Unisys announced that developers and even individual users of noncommercial and free GIF software now owed them royalties.

PNG was originally a “patent-free” reaction to Unisys from the open-source community. It uses a public-domain lossless compression algorithm and supports transparency like GIF. But it improves on GIF by supporting full 24-bit color, which makes it suitable for photographs. Because the compression is lossless, file sizes are larger than JPEG. Line art and graphics with 256 or fewer colors, for which GIF is most commonly used, produces file sizes comparable to GIF.

PNG hasn’t supplanted GIF because Microsoft chose not to support it fully in their Monopoly Standard browser. Microsoft Internet Explorer versions 6 and earlier do not support the “alpha channel transparency” used for color images with transparent backgrounds; all IE versions display incorrect colors in some PNG files (Mozilla/Firefox, Safari, and Opera fully support PNG). I learned that the hard way when I tried to replace the graphical titles on my Travel Photo Essay pages with new PNG versions. To accommodate the majority of my visitors, I had to replace the new headers with GIF versions that don’t look as good. Microsoft Internet Explorer 7 corrects the transparency problem but not the color problem. Better late than never, I suppose. And better to fix half the problem then none.

I used PNG with Paint Shop Pro for the working files I saved while editing images. The lossless compression provided a considerable space saving. Photoshop CS2 and CS3 extend the format to 48 bits, but still don’t allow alpha channels or metadata. The lack of metadata is a major weakness, since it can’t embed a color space or profile.

JPEG 2000 was supposed to be a 21st century replacement for the 1992-vintage JPEG. It uses a superior lossy compression technology that can produce fewer and less noticeable artifacts with smaller file sizes. It also includes a very effective lossless compression option. Despite its advantages, JPEG 2000 has gone nowhere. Seven years after its release, no Web browser supports it natively. Part of the problem may be that the “legacy” JPEG format has proved entirely adequate in very extensive use, so nobody is clamoring for a replacement.

Another difficulty is that image compression algorithms are a minefield of overlapping and broadly-drafted patents, in part due to the understaffed and inept United States Patent and Trademark Office. The committee that created JPEG 2000 claims to have obtained all the necessary rights, and has made “a strong goal” of allowing anyone to implement the basic functionality without royalties. But there is still a pervasive fear that someone might suddenly emerge with an unnoticed and possibly dubious “submarine” patent, and attempt to shake down users the way Unisys did with GIF and Forgent Networks did with JPEG. Forgent’s patent was eventually invalidated, but not before they extorted over $90 million from 30 companies and sued 31 others.

Photoshop CS2 and CS3 support JPEG 2000 through a plug-in that’s included on the CD but must be installed manually. Its lossless mode provides the most space-efficient way to store 48-bit images, and includes metadata and alpha channels. Reading files is very slow. Writing files is excruciatingly slow, as the plug-in makes multiple passes through the file to optimize lossy compression even if you’ve selected lossless compression. A “fast mode” check-box option disables this optimization and makes file writing somewhat faster, but it often un-checks itself and forces you to wait for the useless optimization before you can reset that option. I suspect that JPEG 2000 will go extinct more quickly than other formats, so I consider it useless for archival image storage despite the significant space saving. Few graphics programs can read it, and as far as I know only Adobe’s plug-in can read the lossless 48-bit files it writes in Photoshop. But I use it for saving 48-bit working files while editing images in Photoshop, since Adobe provides no real alternative.

HD Photo is the newest animal in the file format zoo. It’s Microsoft’s answer to JPEG 2000, and offers very similar features and performance. Microsoft originally called this proprietary format Windows Media Photo. But when they decided they wanted to monopolize digital imaging the way they’ve monopolized office applications, they renamed it HD Photo. (“HD” seems to be the faddish name currently applied to any new digital technology whose benefits may not be readily apparent to many who are supposed to adopt it, as in HDTV and HD Digital Radio.)

Since Microsoft only started promoting HD Photo at the beginning of 2007, it’s far too early to predict whether it will fare any better than JPEG 2000. Microsoft built support for it into their flashy new Vista operating system, and they have a “Director of Digital Imaging Evangelism” to promote it. Yes, that’s his actual job title! As proof that “it’s not just for Windows anymore,” they’ve supposedly promised to make the HD Photo specification available for free, and also to refrain from suing developers who implement the patented technology on non-Microsoft or open-source platforms. They’re looking to get the Joint Photographic Experts Group to standardize HD Photo under the proposed name of “JPEG XR,” and offering royalty-free licensing of the relevant patents as an incentive. Microsoft’s control of those patents may actually work in HD Photo’s favor, as their armada of lawyers stands ready to torpedo anyone who threatens a “submarine” attack.

Despite Microsoft’s monopoly power, HD Photo still faces the same uphill battle JPEG 2000 had to convince users that it offers them significant and valuable advantages over established and entirely adequate formats. Microsoft’s “evangelists” also have the particular challenge of selling HD Photo to an inherently skeptical community. Many photographers and graphic designers are Apple Macintosh fanatics who probably won’t be receptive to any proprietary Microsoft standard. And other potential users could be reluctant to submit to Microsoft’s terms and conditions. I downloaded the free Photoshop plug-in; but when the installer presented me with an End User License Agreement full of fine print, I decided that HD Photo probably isn’t worth spending the time to read and “agree” to it. Still, if any company can bully (or “evangelize”) their proprietary format into a monopoly standard, it’s Microsoft. So stay tuned. But I’m not holding my breath.

Finally, PSD is Adobe Photoshop’s native file format. As you’d expect, it supports everything Photoshop can produce, including layers. To my knowledge, TIFF is the only other format that supports layers, although non-Adobe software may have problems reading files with layers. The main disadvantage of PSD is a file size as extravagant as TIFF, multiplied by any saved layers. The only compression it allows is the nearly worthless “run-length encoding” that compresses some sequences of repeated bytes.

PSD is another possible candidate for future-proof archival storage because of the long-standing thorough dominance of Adobe and Photoshop in the graphics market. Some non-Adobe products like Paint Shop Pro can read it. I use when I need to preserve layers in working files.