.dng as preservation format

[Elizabeth England]

(Apologies for cross-posting)

 

I am working on the preservation of a large collection of born-digital photos from the campus photography unit at Johns Hopkins. The photos are currently all saved as jpegs and nef, the Nikon camera RAW. I plan to normalize the photos that the archives will ultimately retain, but have not decided on the preservation file format. The campus photographers have weighed in that they are interested in DNG as the preservation format. I’m not too familiar with DNG, so I’ve been researching it and am wondering if anyone has experience with using it as a preservation format? Thank you in advance!

 

Elizabeth England

National Digital Stewardship Resident

The Sheridan Libraries

Johns Hopkins University

3400 N Charles St

Baltimore, MD 21218

410-516-8787

eeng...@jhu.edu

 

[Seth Shaw]

No personal experience with the format but it is a good option. DNG is an open format for camera sensor data (rather than a processed Jpeg representation) that has a good amount of industry support. I don't think most of the common image viewers can render them but all the major photo editing packages do.

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[Bertram Lyons]

Hi Elizabeth --

We recently completed a format assessment project with Harvard University Libraries and found the DNG format to be an acceptable preservation format for the storage of scene-referred images (those that began life as color filter arrays from digital cameras). 

Digital Negative (DNG) is an open raw image format created by Adobe for digital photography applications. DNG is based on the TIFF/EP standard format, and mandates additional TIFF tags to support camera-specific metadata. Because of its connection to the TIFF specification (which is itself an agreed-upon preservation format for digital still images), we felt that DNG, with certain precautions, can be used comfortably for long-term storage.

Format Lineage:

TIFF Revision 6.0, 1992, Final, Adobe Developers Association (includes Part 2 - Extensions)

ISO 12234-2:2001, Electronic still-picture imaging – Removable memory – Part 2: TIFF/EP image data format

Adobe Photoshop® TIFF Technical Notes

Adobe Photoshop® TIFF Technical Note 3

Adobe Digital Negative Specification (DNG), Version 1.4.0.0, 2012

A link to the format comparison matrix that we used can be found here: https://wiki.harvard.edu/confluence/display/digitalpreservation/Image+Sequence+Formats

Best of luck!

- Bert

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[Tyler Thorsted]

Elizabeth,

We have also adopted DNG as an acceptable preservation format. The format appears to maintain the raw sensor data and majority of the metadata associated with the original format. There are some different versions of the DNG specification, embedding the original and options for lossy compression so find what works for you.

Tyler Thorsted

Digital Conservator

LDS Church History Library

[Joseph Rhoads]

Elizabeth,

To add another data-point.

We have a collection where we preserve DNG files and create several derivatives based on them.

Specifically we're working with the campus Herbarium

https://repository.library.brown.edu/studio/collections/id_654/?per_page=100&page=1&view=gallery

We made the decision to extract the TIFFs and store them as the preservation masters along with the DNGs, but if I were to do it over, I might recommend just the DNGs.

In our case the information in the DNGs is a strict superset of what we get with the TIFFs.

(We also create JP2s for dissemination with an IIIF compliant image server)

-Joseph

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Joseph Rhoads

Digital Repository Manager

Center for Digital Scholarship

Brown University Library

[Matthew Burgess]

As mentioned by others, DNG is an open format. Importantly, it embeds a lot of metadata that is usually contained in sidecar files (such as adjustments) or even locally on individual computers (such as custom camera profiles) when dealing with proprietary formats including NEF and CR2. I would argue that DNG should be a preferred format for born-digital photographs where available.

--
Matthew Burgess
Imaging Officer
Digitisation and Imaging Services
State Library of New South Wales

[Tom Creighton]

Don't know if it's still relevant, but we at FamilySearch have made the decision to switch from normalizing to JPEG2000 to go with DNG. We haven't yet put it into place, but that's the plan. It's unlikely that we'll migrate existing artifacts from JPEG2000 until that format really looks like it is not viable. Since we have millions of still images already in our preservation system, that transformation is not something we will take on lightly.

Good luck to you.

Tom Creighton

CTO, FamilySearch

t...@familysearch.org

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[Kari S.]

Hi Bert,

I see on the Harvard DRS formats wiki that the DNG is preferred for digitized motion-picture film and that for still images they are recommending TIFF (primarily).  Can you discuss DNG as a recommended format for still images?

Thank you,

Kari

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[Bertram Lyons]

Hi Kari --

I think a good overview of Harvard's move towards DNG as one of a set of preferred formats can be found with the initial work of Jack Holm which is found at this link from Harvard's DRS, specifically the TIFF Format Specifications document: https://wiki.harvard.edu/confluence/pages/viewpage.action?pageId=207554565

An Adobe DNG file, at the wrapper level, is a variety of the TIFF format specification (TIFF/EP). The main difference is the array image data stored within the wrapper instead of processed uncompressed color pixels. Additionally DNG recommends a specific set of TIFF tags that should be present within the file to ensure that the array image data can be processed appropriately to color pixels upon rendering.

From a functional perspective, however, I would only keep DNG as a master if I was sure that I had clear and thorough information on how the sensor data should be processed according to the photographer. Or if I had both a TIFF "print" and was keeping the DNG to allow for re-processing at a later date.

Best --

Bert

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[Kari S.]

Bert, thank you for your reply and the extra information.  That helps me a lot. I had read the information based on the work of Jack but couldn't reconcile it with what you had done.  Now I have a better idea.

Best,

Kari