DNG and variety

This page addresses the myth that using DNG in the pipeline between cameras and raw converters prevents satisfactory handling of major or subtle variations in sensor configurations by those raw converters.


What are the problems?

Examples of sensor configuration details:
DNG and camera innovation

Example of contents of a DNG file:
Raw topics

What variety are we talking about?

This page is about:

  1. Variety in camera characteristics, especially sensor configurations.
  2. Variety in raw converters, especially in the methods they use to handle "1".
  3. Variety in photographers' preferences for image quality, workflow, and tools.

There is one potential claim that is true:

DNG can't solve all the problems of these types of variety.

Just many of them!

Alternatives approaches are typically worse.

What false claims are made about DNG and variety?

Some typical false claims include:

DNG is really suitable only for an Adobe-centric workflow.

DNG imposes a vanilla or "one size fits all" policy on cameras and/or raw converters.

DNG restricts raw converters to rendering like Adobe's ACR and Lightroom.


Methods of handling variety

Products can use one method or combinations of methods.

Method 1: Use openly-specified data in the DNG file

Adobe's ACR and Lightroom use "method 1" by default, but allow users to use "method 3" as well by providing their own "Calibration" values to modify the default colour rendering.

A key reason why DNG is not "just another raw file format" is that DNG files contain openly-specified metadata that describes many of the camera characteristics, especially sensor configurations. This is especially useful for archival purposes, and for processing raw files of cameras that are unknown to the raw converter.

It is possible to render a DNG-held image to at least the quality of Adobe's ACR and Lightroom, and not limited to that quality, using just this openly-specified data.

Method 2: Use "secret sauce" in the DNG file

Adobe's DNG Converter copies an Exif Makernote block if it exists to DNGPrivateData, allowing raw converters to access it.

In a stagnant and non-competitive world we wouldn't have "secret sauce" in DNG files. We don't live in that world.

DNG permits a camera manufacturer to store private data in the DNG file. Or a DNG converter can copy private data that is in a non-DNG file to the DNG file. Then raw converters can read that data, if they understand it. (If they don't understand it, or don't need it, they can use "method 1" and/or "method 3". The openly-specified metadata must be present even if there is "secret sauce" as well).

Method 3: Use data that isn't in the DNG file

Here is more about the data that raw converters need and their options for adding DNG support:
Camera details embedded in DNG - end notes

Some raw converters use their own data about the camera to supplement the data in the DNG file. They may do so instead of "method 1", (for example, ACDSee, Pixmantec's Rawshooter). Or they may do so as well as, or as an optional alternative to, "method 1", (for example Silkypix or Apple's Aperture). This data may be built-in by the raw converter supplier or be set by the user.

This is explicitly supported by the DNG specification's tag UniqueCameraModel: "This string may be used by reader software to index into per-model preferences and replacement profiles".

Method 4: Evolve the DNG specification

DNG is designed to evolve. It has a version scheme that allows the DNG specification, DNG writers, and DNG readers, to evolve at their own paces. (All versions remain valid so that old photographs can be processed in future).

The 2nd version added about 10 new tags, some of them providing more details about camera characteristics. There will be more versions in future. Each new version increases the variety that can be handled by "method 1".


Examples from Silkypix

Silkypix is used here as an exemplar of both "method 1" and "method 3". It probably isn't unique, and there is no reason why other raw converters couldn't do something similar.

D70 NEF DNG from D70 NEF Linear DNG from SD14 X3F SI-1920 DNG

"Native" Nikon D70 NEF.

Silkypix offers a choice of renderings if it knows the camera.

"Converted DNG" from Nikon D70 NEF.

Silkypix offers both "native" rendering and "DNG" rendering if it knows the camera.

"Converted (Linear) DNG" from Sigma SD14 X3F.

Silkypix offers a choice of renderings if it doesn't know the camera, even for Linear DNG.

"Native DNG" from Silicon Imaging's 1920HDVR digital movie camera.

Silkypix offers a choice of rendering if it doesn't know the camera.


Examples from Capture One 4

Although this is still in Beta (at 2007-09-03), Capture One 4 is used here as an exemplar of both "method 1" and "method 3".

D70 NEF DNG from D70 NEF

"Native" Nikon D70 NEF.

Capture One 4 offers a choice of "Profiles", with an appropriate default.

"Converted DNG" from Nikon D70 NEF.

Capture One 4 offers a choice of "Profiles", including those for specific cameras, by default using a rendering specific to DNG.


Examples of misleading or false claims

Both of these examples were cited months after they were first posted, showing that they had an extended influence. My aim here is to counter misinformation and "fear, uncertainty, doubt".

Claims Commentary

Michael Tapes: RawWorkflow.com, 2007-04-03. (Cited: DPReview, 2007-07-20).

But if RSP "had" supported all DNG files, then those not natively supported by RSP would have converted as if Adobe had done them....

So while Adobe would want you to believe that a true DNG savvy converter is a wonderful thing, it is only a wonderful thing if you want to have Adobe quality conversion (debayer) and color.

DNG doesn't dictate the colour rendering or demosaic (debayer) algorithm. Even different versions of Adobe's software don't always render DNG files the same and sometimes have different demosaic algorithms.

It is also possible to have user-specified modifications to DNG's default colour rendering.

But for now this is only valid for an Adobe workflow IMO. It also works for Silkypix and others!

Joseph S Wisniewski: DPReview, 2006-11-25. (Cited: DPReview, 2007-07-20).

So, "full DNG support" means the decoder has to have a collection of oddball algorithms to cope with the features of the "fringe" cameras. And this fringe algorithm collection needs to be updated every time someone brings out a new fringe DSLR.

According to that logic: " full support by any raw file formats means the decoder has to have a collection of oddball algorithms to cope with the features of the "fringe" cameras. And this fringe algorithm collection needs to be updated every time someone brings out a new fringe DSLR".

That is simply a description of "variety in the digital photography industry". It isn't a problem caused by DNG, but it is a problem that DNG can help solve.

The only problem is that there's no such thing as "full DNG support".

It is true that "there's no such thing as "full DNG support"" yet, but so what? (And is there full support of any other raw file format?)

What matter is whether there is enough DNG support at any time to cater for the DNG files in use by photographers.

No one except Adobe uses the color profiles embedded in the DNG files. Many products can support cameras via DNG that they can't support via their native raw files. There is no evidence that they all ignore color profiles embedded in the DNG files. (dcraw bases its colour rendering data on DNG's method).
That's because the entire DNG concept is flawed, it doesn't solve any real world needs. The DNG concept solves real world needs for many people. This doesn't need further commentary here.