File Preservation of Digital Images

The troubles of file format preservation can be especially hard for such professions as photography. Photographers must deal with not only a lack of a hard copy of their work but also the issues of proprietary file formats with camera manufactures and image editing software. For example, the Nikon .NEF file used, as the company’s proprietary camera RAW file format will not even open in such systems as Adobe Bridge depending on the year the camera was produced and the version of .NEF file provided.

This could render collections of photographs useless. To help evade such issues the Digital Image Submission Criteria (DISC) standards have been provided by the IDEAlliance. The DISC standards recommend that of a JPEG high quality (level 8 ) and DNG a more universal RAW file format as delivery file formats (64).  These file formats are acceptable for file delivery but are they archival? This question can be answered by expanding upon our current knowledge of archival formats.

According to the Sustainability of Digital Formats Planning for Library of Congress Collections to be considered for archival status, certain aspects of the file must be measured. The first is disclosure; this means the amount of documentation that exists of over the created file (par 3). If it is an open source file format, there is more information than that of a proprietary allowing for the proper amount of information for a file to be properly preserved. Files are also measured on their adoption, if the format is widely used it allows for longer life in the digital world (par 7). Transparency “refers to the degree to which the digital representation is open to direct analysis with basic tools, including human readability using a text-only editor” (par 10).

Another factor is whether a file format allows for self-documentation through metadata, the idea being that if you can write within the file there may be clues on how to keep in an expectable condition for later use (par 16). It is also important to mention that external dependencies of the file type, if the file depends to much on specific hardware it may be tough to continue use if a digital system needs to be upgraded (par 20). Lastly, any patents and technical protection mechanisms must be considered to make sure that there is always access to the file and that multiple users are still able to obtain and work with it (par 22).

In regards to the DNG file format is considered to pass many of the requirements offered by the Library of Congress. “DNG is publicly documented, it is far more likely that raw images stored as DNG files will be readable by software in the distant future, making DNG a safer choice for archival” (Adobe Systems Incorporated 10). The public documentation of the metadata of the DNG file is also readily available allowing software to continue to read the files in the future (Adobe Systems Incorporated 10). As an extension of the TIFF 6.0 file format it is also compatible with the TIFF-EP standard and if necessary can “simultaneously comply” with the Digital Negative Standard as well (Adobe Systems Incorporated 10). This means that not only should file reader except a .DNG extension but also a .TIFF extension, opening up image storage into TIFF files as well (Adobe Systems Incorporated 11).

The color maintenance in the DNG file is rated to be excellent and allows for support of ICC profiles (Library of Congress par 4). This is very good when putting these files into a cross media workflow because it allows for the support and conversion of color profiles upon output. DNG also offers a way to create a standard way to encoder the raw sensor data from the camera and a few manufactures have begun to include DNG as an option for capture (OpenRAW Organization par 7). The format of the file is also intended for nondestructive image editing allowing for “for use with image manipulation tools that execute a variety of processes to transform the DNG into “pictures” suitable for different outputs” (Library of Congress par 4). Currently the compression of the image files is minimal when working with in the DNG format (Adobe Systems Incorporated 15). Transparency of the file is found only within the wrapper and any encoded data needs tools render (Library of Congress par 3).

Regarding the JPEG, file format is similar to the RAW in that it is fully disclosed and is documented by the Joint Photographic Experts Group (JPEG) (Library of Congress par 3). It has also been documented in the ISO standard in ISO/IEC 10918-1:1994 (JSTOR par 1). The transparency of the JPEG depends upon the type of software it does not have any external dependencies when it comes to reading or using the file (Library of Congress par 3). The file format has limited ability for technical metadata this would include such things as f-stop and aperture (Library Congress par 4). Color maintenance is limited and according to the Library of Congress does not support all ICC profiles.

The appeal of the JPEG file format that unlike DNG, the file format contains wide acceptance for digital capture and can be found in almost every camera or scanner as a capture option. However, even though the file format is available for capture it is not suggested due to the lossy compression when capturing data (Library Congress par 6). It should be noted that on some digital cameras there is an option for high quality jpeg. “It is using the same resolution as the RAW setting, assuring maximum image quality” (Smith par 5). Currently, Adobe Photoshop allows for JPEG and TIFF files to be opened and edited in the Camera Raw dialog (Adobe par 2).

Both the DNG and JPEG formats can be found to be file formats that are acceptable for long term preservation of files. However, it is important to note that each file has an appropriate place within the cross media workflow. The DISC standards make note that the DNG and JPEG are appropriate method of delivery and does not mention capture. However, if when capturing digital file formats it is important to use the highest quality possible so this maybe when a worker within the CMW uses a DNG file.

Due to the limited bit depth of the JPEG a DNG might also be best when editing images within the CMW. However, when a preview of an image is needed in the CMW a JPEG file with its compressed format would be ideal for fast loading time. Also if working with a website in a CMW a JPEG file format would be an excellent deliverable for such an output. It is important to note that were the final file will end up is the path it should follow within the CMW.

It is important to evaluate and migrate what is needed/wanted at least every five years when working with digital files (Gyor par 8). It is also important to pay attention to industry trends when working with files so that as formats fall out of favor the information they contain can be migrated over to a file format that allows for better preservation. By paying attention to what makes a file long lasting you are able to then extend the life of not only your files but the cross media workflows, content management systems and digital asset management systems that support it.


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