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Tuesday, February 26, 2013

DNG File Format & DNG Converter

In this excerpt from his book, digital master photographer and Photoshop Alpha-tester Jeff Schewe demystifies the DNG format for today and for the future


Digital Image Preservation

• Self-documentation: Digital objects that are self-documenting (meaning containing information relating to the content and the format of the file) are likely to be easier to sustain over the long term and less vulnerable to catastrophe than data objects that are stored separately from all the metadata needed to render the data as usable information or understand its context. A digital object that contains basic descriptive metadata and incorporates technical and administrative metadata relating to its creation and early stages of its life cycle will be easier to manage and monitor for integrity and usability and to transfer reliably from one archival system to its successor system.

• External dependencies: The degree to which a particular format depends on particular hardware, operating system, or software for rendering or use and the predicted complexity of dealing with those dependencies in future technical environments.

 Impact of patents: Patents (a form of intellectual property) related to a digital format may inhibit the ability of archival institutions to sustain content in that format. Although the costs for licenses to decode current formats are often low or nil, the existence of patents may slow the development of open-source encoders and decoders, and prices for commercial software for transcoding content in obsolete formats may incorporate high license fees.

• Technical protection mechanisms: To preserve digital content and provide service to users and designated communities decades hence, custodians must be able to replicate the content on new media, migrate and normalize it in the face of changing technology, and disseminate it to users. Content for which a trusted repository takes long-term responsibility must not be protected by technical mechanisms such as encryption or implemented in ways that prevent custodians from taking appropriate steps to preserve the digital content and make it accessible to future generations.

As you can see from these seven sustainability factors, digital photography is at serious risk. Why? Undocumented, proprietary raw file formats. Some may argue that there are file formats available that do mitigate the risks; those file formats (such as JPG or TIFF) don't provide a format for the storage of the unprocessed raw sensor data. But it's the original raw sensor data that we need to preserve because, as we've seen in just a few short years, the software for processing the raw data has improved considerably. With digital photography, we have the unprecedented situation that original raw captures will actually improve over time because the software and algorithms to decode and access the raw data will improve over time.

Based on the NDIIPP sustainability factors, the DNG file format rates very highly for the prospect of long-term preservation and conservation of digital negatives.

How did this situation come to pass? In the history of photography, it has been the traditional role of film or paper manufacturers to develop standards relating to the preservation of photographic materials. The camera makers have had no such responsibility and have developed no such standards. Camera makers have neither the facilities for testing nor any background or experience in long-term preservation. When the digital photography revolution began, the camera makers found themselves in the unusual and rather awkward situation of expanding their traditional role of producing cameras and lenses into a role of processing the digital captures. Based loosely upon existing TIFF standards (in particular, TIFF-EP standards), the camera makers created short-term solutions to deal with technical issues of writing raw sensor data to disk or storage. Each sensor type and its raw file format was designed for the purpose of solving the short-term problem of writing the data. Little or no thought has been given to working toward standards that would help ensure long-term access to the data.

The camera makers, so far, are failing to address the long-term preservation of digital photography by their persistent use of undocumented and proprietary raw file formats. This must change. Standards must be developed and adopted that ensure sustainability of digital photography. This is the camera makers' new responsibility, and if they don't adopt it willingly, they must be forced to adopt it by the photographic industry.

Okay, I'll get off my soapbox now.


 

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