You either get it or you don’t
Barry Pearson writes about Seven years of writing about Digital Negative Format and other tales of the life and advantages of the DNG format:
When Adobe launched DNG on 27 September 2004, it was obvious to me that this was addressing a significant need. I knew from my career in helping to develop complicated multi-vendor computing systems that it is very important to structure a system into components linked by documented common interfaces.
I spent about 2 weeks examining the available documentation about DNG, including the specification, before concluding that it was a credible proposal. On 10 October 2004 I began to use DNG for all my raw images.
I had been reading and contributing to newsgroups for many years. Misleading and/or inaccurate statements about DNG began to be posted about 3 October 2004. (This has been a continuing trend all over the web).
I wasn’t that early an adopter, but almost. For me it was the release of Photoshop CS2 that made me switch to DNG, so that would make it April 2005, and high on my list were (and remain) a preference for embedded metadata over sidecars and for having an embedded preview. I still keep my raw files, somewhere, but isn’t it amazing that in 2012 a major camera company can release a professional camera without even offering as an option a publicly-documented raw file format?
Another issue with DGN is that it loses some metadata. For example, Apple’s Aperture can show the focus point grid and the active focus point as an overlay on the image. But it can’t do that with DNGs converted from the original RAW.
Bob
That’s incorrect. The camera makers’ proprietary metadata is preserved in the DNG. Aperture can read raw files’ focus points because they have access to the camera makers’ SDKs, which obviously don’t handle DNGs.
John, are you sure you’re sure? I just experimented again with a .CR2 in Aperture – I can see the focus points. When that file is converted to .DNG, I can’t.
Bob
Sorry, there’s a little misunderstanding. What is incorrect is that DNG loses some metadata – it simply stores all unparsed metadata in a single block. Obviously Aperture displays the focus points for the CR2 but not for the DNG created from it. However, Aperture uses the camera makers’ SDKs to display the focus points and while it recognises your DNG came from a Canon, it doesn’t invoke the Canon SDK code (I think that’s it, but it may be that it does so but the code doesn’t know where the focus point data is stored).
OK. So in the end, converting to DNG robs me of information in Aperture I would have otherwise had. Maybe there are other circumstances I’m not aware of that might do the same for other data/features.
And I’m not convinced that we’ll somehow lose the ability to read CR2 and NEF files at some point in the future. I just don’t see the value of DNG and I see the harm.
CR2 and NEF, perhaps not, though that’s a narrow and short term view of what DNG is about. Just consider whether other camera makers today will continue to be around. Conceivably you will always be able to find some utility on some OS to decode Kodak raw files, for instance, but the app you want on your computer?
In any case, future readability is just a straw man argument rolled out by those who will probably never get DNG. DNG’s advantages are wider than that. Consider metadata entry – embedded metadata is more dependable long term than sidecars, and I’d always be more confident when an app writes metadata to a format that’s publicly documented like DNG (are you really happy Aperture can write directly into mystery meat proprietary file formats?). You also have one or more adjusted previews. So for example I could switch to Aperture and use preview mode to see my Lightroom adjustments, maybe print them too (not sure). And there are the DNG validation hashes – Lightroom doesn’t expose it as much as it might, but it does routine check the data integrity. So it’s a range of advantages.
You are absolutely right, it is hard to believe that professional cameras from major companies like Nikon, Canon, Sony and Hasselblad still come out without built-in DNG support. Pentax and Leica have natively supported DNG for ages. For me, always having to convert to DNG slows down my ingest process quite a bit.
But there is a major issue with DNG: As far as I know, DNGs usually (i.e. by default) store the data as it came from the sensor. That means the application that reads the files needs to support the native format of the sensor pixel pattern. It is quite likely that some software vendors in the distant future will choose not to implement support for exotic historic sensors that do not use a conventional Bayer pattern (like Sigma’s Foveon, the rumored Fuji X-Trans and the like). While it is indeed possible to activate demosaicing in the conversion options inside the Adobe products, that will obviously no longer store the original sensor data and makes it impossible to benefit from improved future demosaicing algorithms unless you accept the storage overhead of embedding the original RAW file. Plus, most people don’t even know the demosaicing option is there, let alone what it does, and it will probably result in larger files as well since the red and blue channel hast to contain the additional interpolated values.
Don’t get me wrong, DNG is great and I wish it was more universally supported, but it is quite dangerous in that it tricks people into thinking all DNG files are 100% future-proof without restrictions.