Archiving Digital Imagery for the Long Haul—Part Two of Four

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File Formats

The most common file formats used today for photographic applications include JPEG, TIFF, DNG and an assortment of proprietary RAW formats. There are others including PNG, GIF, BMP, PSD, PSP and a few more, but for archiving purposes it’s more sensible to stick with JPEG, TIFF, DNG and RAW. It’s well worth noting that the universality of the aforementioned file formats will change over time and at some point you will most certainly migrate your archive of JPEGs, TIFFs and other files to whatever format(s) become the new kids on the block.

Even at this juncture, many TIFFs and JPEGs created in the early days of digital imaging are proving to be difficult to open due to the many changes—subtle and not-so-subtle—in software upgrades over the years. By copying archived image files over to newer storage media, these pitfalls can be greatly reduced.

It should also be noted that file formats can be broken down into two groups: Lossless, which can be repeatedly edited and saved anew without compromising the image quality of the picture, and "Lossy" files, which as the name infers, lose integrity each time they are edited and saved. (Studies show lossy image files such as JPEGs can become visibly compromised after about 10 edit-and-save cycles, depending on the degree of editing performed each time around.

Data Loss:  Watch the file become progressively more compressed.

JPEG

JPEG (Joint Photographic Expert Group), an 8-bit file format, is the most universally used imaging format. Almost every digital camera creates them, and they are universally readable in every photo-editing application. JPEGs are also universally accepted for Web use.

From a storage point of view, JPEGs are attractive because even when saved at the highest quality levels, JPEGs close up smaller than other file format, which means you can archive more images onto whatever drives you may be using.

Despite claims of the inferior image quality of image files saved as JPEG, this is only true in the case of JPEGs saved to extreme compression ratios. JPEGs saved at the highest quality levels (11 or 12 in Photoshop) equal (or at the very least approach) the image quality of the same image saved as a TIFF file.

The real problem with JPEGs is that unlike other file formats, JPEGs are lossy, which means they shed data every time they are edited and saved and as a result can be easily compromised in terms of visual integrity. JPEG format is also not recommended for photographing line art.

Note: JPEGs that are opened and closed without changes remain intact. It’s only when an image is edited (i.e., cropped, color-corrected, sharpened, etc.) that you lose image data.

When shooting JPEGs it’s a good idea to leave the original image files intact, and only work on copies of the original image files. This is the easiest, safest method of preserving the integrity of the original JPEG file. It’s also a good idea to save an edited JPEG as a TIFF, which is a lossless file format that is far more stable than a JPEG.

JPEG2000

JPEG2000 is an advanced, heavier-duty version of the JPEG format. Among the advantages of JPEG2000 are the option to save lossless files, as well as the ability to save files as higher-dynamic 16-bit files (standard JPEGs are 8-bit only).  JPEG2000 also has a feature called Smart Decoding, which enables you to access and decode select portions of the original image file in order to produce multiple high-res or low-res images, which is a valuable tool for videographers seeking smooth zoom and panning action from still images à la Ken Burns.

Though many institutions, including major universities and the Library of Congress, have chosen JPEG2000 as their format of choice for archiving needs, JPEG2000 has been met with luke-warm reception among manufacturers and consumers since it was first introduced in 1996, which makes JPEG2000 an iffy choice for long-term image archiving.

TIFF

Like JPEG, TIFF files (Tagged Image File Format) are a universally recognized imaging standard and can be opened and edited on most all image editing software applications. One of the key advantages of TIFF files over JPEGs is that unlike JPEGs, which are exposed to data loss every time they are opened, edited and saved, TIFF files can be repeatedly edited without suffering any form of image degradation. They can also be edited and saved as 16-bit files, which contain far more tonality than 8-bit JPEGs.

The downsides of TIFF files are that because TIFF files do not compress when closed, a TIFF file takes up far more storage space than other file formats. As a workaround, TIFFs can be saved using a lossless compression option called LZW, which works as advertised, but because it’s not universally supported in the industry, TIFF files saved using LZW compression might be problematic to open down the line if LZW compression technology gets lost in the shuffle over time.

Note: TIFF files are not supported by most Web browsers and even if they are, TIFFs are far too large for most Web applications. Stick with JPEG for any and all Web applications.

RAW

The beauty of RAW files is that they contain virtually every “bit” of image data captured by the camera, and when processed properly and intelligently in Photoshop or similar proprietary image processing software, can produce TIFFs and JPEGs containing higher levels of tonality, contrast and detail than comparable TIFFs and JPEGs captured in camera.

The iffy aspect of archiving RAW files is that RAW files are proprietary to specific makes and models of cameras from a number of camera manufacturers. As such, the lack of standardization means many RAW file formats will undoubtedly fall by the wayside with time and may not be easily accessible with the passage of a decade or two.  This is not to say one shouldn’t archive RAW files, but if you do, be sure to include hi-res JPEG and/or TIFF files along with the RAW originals.

DNG

DNG is a TIFF-based image file format designed by Adobe that converts RAW files into a format that contains all of the RAW file data along with all metadata for the original image file and a color-corrected JPEG preview image. When processed in Photoshop, DNG files are opened in Adobe Camera RAW and can be edited using the same tools Photoshop makes available for conventional RAW file image editing.

The advantages of DNG files is that being universal, not to mention being a format created and supported  by Adobe, DNG files will probably withstand the test of time better than many RAW file formats. Another selling point for DNG files is that they take up less storage space than RAW files without compromising image quality.

A recommended set of archiving guidelines based on current technologies would be as follows:

  1. The original RAW files as captured by the camera. If your originals are JPEG or TIFF files, these should be left unedited and treated the same as RAW files.
  2. Process and edit each RAW file and save as a full-size JPEG at 300 dpi. Some (including myself) also save the same file as a same-size, 300-dpi TIFF for reasons of stability and as an extra measure of security.
  3. By storing the original image file along with a full-size, edited JPEG and/or TIFF of the original RAW (or JPEG) best assures that the image will be easily accessible, years or decades from now.
     

Related Articles:

Archiving for the Long Haul, Part 1

Archiving for the Long Haul, Part 3

Archiving for the Long Haul, Part 4