Why I don't delete my NEFs

Adobe DNG icon

Someone asked on Flickr if they should delete their camera raw files after converting to Adobe DNGs. Certainly you can see a strong pressure from Adobe to do so in order to save some hard drive space.

I don’t. Adobe’s DNG converter has the option of storing the original raw file along with it so I don’t see any theoretical harm in deleting the RAW file if that option is checked. Then again, since it increases the file size as much as two files stored separately, I don’t understand the advantage in that other than in file management for those who don’t have an adequate one (i.e. you are using Adobe Bridge or iPhoto instead of Aperture or CaptureOne).

The problem is that without this option checked can you reconstruct the original raw file from the DNG alone? I know of no tool that does this. I know of no incentive for one to be built by Adobe.1

So what? Well look at the DNG file, it is double the size of a compressed NEF (Nikon raw). Why? Because Adobe’s de-mosaic recipe has already been added/embedded with the RAW.2 What if I don’t like Adobe’s recipe?3 What if I’d prefer my vendor’s RAW conversion because they are aware of their own anti-alias/bayer filter and optical design assumptions in their lenses and bodies? What if I use a a 3rd party tool made by real optics engineers that adjust for lens and camera body defects? What happens as these RAW processing tools improve? What option do I have at that point?


I use DNG as part of my photo workflow because unlike TIFF, they can carry metadata. I store and archive DNGs along with the Nikon NEFs in Aperture. But will I don’t delete my NEFs.

And neither should you.

1 One day I switched to Outlook Express. It was very easy to move my e-mail from Eudora to it and I liked the nice mac-like UI (pre-Mac OS X) and appreciated the speed and search-ability of a database storage system instead of a file/folder one. The problem came what I wanted to leave. The only way to extract my e-mails and address book information was via a AppleScript that took hours to run and did a half-assed job of it. I learned a lesson there: Outlook Express was a roach motel. Is DNG any different?
2 I am not saying that this application from the DNG can not be theoretically reversed to recreate the raw file or that Adobe is doing irreversible changes to the raw file format. Actually the main strength of DNG is that it tries to keep all the metadata and raw sensor data intact (as much as it is mappable). There is a world of difference between the theoretical and the practical however.
3 I don’t like it. Adobe Camera Raw applies denoising, contrast adjustment, and sharpening to hide its inherent inferiority—these are post-processing, not development tools, but this significant detail is missed by people who rave about how great ACR is.

11 thoughts on “Why I don't delete my NEFs

  1. Apparently this post confused the questioner. Here is a less politically-correct, more opinionated response that has some stuff I was saving for a future blog entry.

    @Gordon: DNG is future-proofed and hardware-independent. It is also a very simple specification to implement (it’s just TIFF spec with a standardized metadata format). It is because these advantages that it is useful. Imagine if your camera comes from a vendor that might go out of business, or Canon decides to stop supporting your old digital camera, or your image editing tool is made by someone really lazy.

    But hardware independence is a BAD THING(tm). An NEF converted into a DNG has the unique camera data as a string (like “Nikon D50”) in the header field. For all intents and purposes, that file is identical to the Nikon D70s NEF converted to a DNG, other than that string. Applications that process and handle DNGs will handle images from both cameras identically. It will handle images from different lenses identically. It will handle almost any image from any digital camera nearly identically. DNG is an attempt to treat all images almost identically.

    (There are some arbitrary parameters in the DNG spec such as “anti-alias filter strength” that can make a difference in processing, but these are qualitative numbers, not quantitative and thus aren’t camera-specific, aren’t accurate, and aren’t precise.)

    The problem is cameras aren’t identical.

    The Nikon D50 and Nikon D70s RAWs are not the same and shouldn’t be treated as such. The anti-aliasing bayer microlenses placed in front of the sensor and the exposure system are different between those two cameras. Nikon Capture 4 knows this and treats them with a slightly different recipe when processing. DxO Optics Pro does the same and even adjusting for lens defects and lens-body combinations.

    You need the NEF file to take advantage of either program. Can you reconstruct the NEF file from a DNG file? No.

    Sure, replacing your RAW files with DNGs is a view that is shared. It is shared among people who think that a RAW file format is no different than a TIFF with metadata who “rave” about how “great” Adobe Camera Raw is.

    Among those of us who know better, doing so is just buying into some Adobe marketing bullshit.

    DNGs are future-proofed and hardware-independent and that is a great thing. They are not your digital negatives and should not be treated as such.

  2. I agree completly.
    I actually don’t convert to DNG. Mostly because I do use Nikon Capture and then “transfer” to Adobe if I need further processing. I found I am willing to put up with it’s slowness (which isn’t so bad on my dual CPU PC) for it’s better more pleasing results.
    Though the thought of support for NEF or whatever other format going away is real. I dought that a company going under will mean instant loss of support for the file format from other vendors like Adobe.

  3. There are some inaccuracies above. Here are some corrections:

    1. It says: “Because Adobe’s de-mosaic recipe has already been added/embedded with the RAW”. Not true, (unless a specific non-default option has been requested). By default, (whether or not the original raw file is embedded), the DNG file contains the original sensor data, ready for any raw converter to process as it chooses.

    2. A reply says: “But hardware independence is a BAD THING(tm)…. It will handle almost any image from any digital camera nearly identically. DNG is an attempt to treat all images almost identically”. Most certainly not true! For example, if the D50 and D70s had a different colour response, the calibration tables in the DNG file be different. A DNG file contains the original sensor data, plus lots more information which identify the specific characteristics of the camera concerned, for example colour response, anti-aliasing amount, sensor configurations, and many others. Where cameras need to be treated differently by the raw converter, the DNG file is intended to hold the detailes that the raw converter needs to do so.

    3. The same reply actually added: “The anti-aliasing bayer microlenses placed in front of the sensor and the exposure system are different between those two cameras. Nikon Capture 4 knows this and treats them with a slightly different recipe when processing”. So what? DNG doesn’t lose anything, it adds metadata! A raw converter can either use the camera name such as “D50″ or D70s” to make its decisions, if it knows about the camera, or use the “anti-alias strength” if it doesn’t know about the camera. More, not less, choice.

    A DNG file contains a superset of the contents of a NEF, even when the original isn’t embedded.

    1. @Barry Pearson: Thanks for the corrections!

      Sorry about my errors. I should have been more clear that Adobe DNG doesn’t by default overwrite any data that is already there, it adds metadata and encapsulates the whole schmeer in its container format.

      I believe I addressed that embedding the entire RAW is a lose-lose in two ways: a) you are dependent on software to re-extract the raw file if you need it (for DxO, Nikon Capture, etc), and b) you almost double (sometimes more than double) file size.

      My point is while theoretically the real RAW file is recoverable, it is de-facto not. Adobe DNG creates a crutch that is going to vanillafy the camera industry. Honestly, is it a surprise that things like lens correction and de-vignette weren’t in the DNG specification first but were driven by Olympus et. al. and then added to the DNG specification? It isn’t to me. And yet, Leica had de-vignette in-camera (but not in-RAW) long before this trend—and Leica wrote to DNG. Hmmm…

      In general, taking the calibration support you mention is that either you embed the support in explicitly in which case any software supporting DNG pretty much uses it as a crutch, or you leave it as a hint, in which case you have all software pretty much goes with ignoring it (except Adobe software).

      The "so what" reason is there is the theoretical and practical and this article seeks to address the latter. I know in the former, by default, you can theoretically extract all the original RAW data from the DNG (because it is a superset), but since the invention of DNG five years ago how many unconverters have there been. By this I mean extraction, without embedded original RAW, from DNG to say an NEF or ORF or RAW or CRW? The answer would be none. And if someone deleted their NEFs and kept the DNGs and suddenly discovered DxO or Nikon Capture and liked it’s postprocessing, what recourse would they have? The answer would be none.

      Now compare it to the reverse case. Let’s say they left their data in NEF format, and they decided they really liked ACR processed images. What recourse would they have? Oh that’s easy—download DNG converter, convert the image, and then view in ACR… wait, they don’t have to do that: they can just view in ACR. It’s not like Adobe is going to remove support.

      See what I’m saying? Unless DNG is the default format of the camera, it’s a one-way street. People recommending it are basically saying, "Adobe is going to win. The rest of the camera world is going to lose." That may be the case, but, I like to root for the underdog. They’re the ones making the hardware, they’re the ones with the incentive to innovate.
      My recent post LH-3 Lens hood for the 35mm F1.2 NOKTON

  4. The only thing DNG “future proofs” is Adobe profits. They have a long history of planned obsolescence by design coupled with abandoning support for last year’s Adobe products. Where’s the CS2 upgrade for the D3 and D300 . . . CS2 owners have already been abandoned.

  5. Hello!
    Very Interesting post! Thank you for such interesting resource!
    PS: Sorry for my bad english, I’v just started to learn this language 😉
    See you!
    Your, Raiul Baztepo

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