Workflow Friday: To DNG or not to DNG?


The Digital Negative (DNG) file format created by Adobe is an open source "archival" file format for raw digital images. It was created because Adobe noticed that some file formats were starting to disappear, and some raw processing software options were not supporting those older out-of-date file formats anymore. For example, Kodak, who is now in bankruptcy, had raw file formats for their 14n full-frame camera that are no longer readable by many manufacturer’s image editing software. This is just one example. Canon has also canned the original EOS 1Ds file format and there are only a few image-editing programs that can still read that raw file format. Hence, if you want access to your images in the distant future then this is a huge topic of discussion and one that many photographers still debate. Before we get into the debate let’s discuss the pros and cons of the DNG file format.

The key benefits for photographers are (note that the first three benefits are from the Adobe DNG website):

  • DNG format helps promote archival confidence, since digital-imaging software solutions will be able to open raw files more easily in the future.
  • A single raw processing solution enables a more efficient workflow when handling raw files from multiple camera models and manufacturers.
  • A publicly documented and readily available specification can be easily adopted by camera manufacturers and updated to accommodate technology changes.
  • The DNG files are roughly 10 to 40% smaller than the original file format. This might seem scary but it is just the application of lossless compression.
  • The DNG files themselves are an all-in-one type file format, which contain a jpeg preview, the raw settings (Adobe Camera Raw or Lightroom settings), all metadata and keywords and the image file itself. What this means is you don’t have to keep track of the .XMP files created by Lightroom and Adobe Camera Raw if you convert to DNG.
  • When creating the DNG file there is an option to embed the original raw file from your camera manufacturer into the DNG file. Doing so will make the DNG file roughly twice the size of your original raw image file but this is perhaps the most archival form of the DNG.
  • The ability to store an updated preview of the image in the DNG file that accurately represents your latest non-destructive raw image settings.
  • Easy conversion options built into Adobe Lightroom and Photoshop.

Basically the thinking here is that the DNG format is an open format that is publicly accessible and should Adobe go out of business this format is easily adopted for future use by any and all that wish to use it, thereby allowing photographers to access their images saved as DNG raw image files at any time in the future. In contrast, the raw file formats for Nikon, Canon, Olympus and other camera manufacturers are "closed" file formats. They are proprietary in nature and the camera manufacturers don’t want to make them open source file formats as they incorporate the secret sauce of their respective manufacturers.

Every Nikon and Canon camera has a different raw file format even though the file extension is the same .NEF or .CR2. For example, a Nikon D4 has a different raw file format than a Nikon D800 even though both cameras have the same .NEF file extension for raw images. With so many file formats running around it is easy to see why the DNG file format is a smart idea. I have heard some of the manufacturers say that using the DNG format in their cameras limits what they can do with the file format—and to some degree they have a good point. But, I think the bigger picture is they just don’t want to lose control of their file formats and also, some camera manufacturers, like Nikon, sell software to process their raw images and they want to make money off that software. But before we get sidetracked here let’s get back to the pros and cons of the DNG format.

The downside to the DNG format includes:

  • For Nikon users, the major downside to using the DNG file format is that Nikon Capture NX2, the software created by Nikon to process their raw files, does not work with DNG image files. So if you are like me, and sometimes want to process an image in NX2, and you’ve converted all of your raw files to DNGs then it is a no go situation.
  • Even though it is an open format, Adobe is just as likely (if not more so) to go out of business as Nikon or Canon. What happens then? The answer to this question is dubious though one assumes that Adobe would submit the DNG file format to become an industry standard. That is an assumption though and while I am sure it would all work out, no one really knows what would happen if Adobe wasn’t around to support the DNG file format.
  • Another downside to DNGs is that it takes longer to import your images into Lightroom since the software has to convert the image file format to DNG, then save that format to multiple hard drives, import the image into Lightroom and create the preview. There is just one extra step to create the DNG, but this is not a quick process.
  • Lastly, there is just a feeling you get when you alter a raw image file. We are told to never alter the raw image file and Adobe goes to great lengths to say that Lightroom is non-destructive so there is this mystique about converting to DNG that feels wrong. If converting all of your original raw image files to DNGs doesn’t sit well with you the best option is to save the converted DNGs on one hard drive and the original raw image files on another—that way you are backed up with both options.
  • Now, after all this discussion, I’ll offer my reasons for not converting my raw images to DNG. I do not convert my raw image files to DNGs mainly because Nikon Capture NX2 does not work with DNG files. And on the rare occasion that I need to work up an image in NX2 it is nice to have the original Nikon raw format. The reason I might work up an image with NX2, instead of Lightroom, is that every raw processor has a slightly different color palette. For some images NX2 renders better colors—actually, for all images NX2 renders better colors right off the bat. The problem with NX2 is that it is a very slow and obtuse piece of software (on the Mac platform) when compared to Lightroom, and it cannot recover highlights nearly as well as Lightroom’s "Whites" slider. NX2 offers slightly better raw processing of the raw image if you really compare it pixel to pixel with Lightroom but that gap is so infinitesimally small, especially now with Lightroom 4, that it is a non-issue for me. Normally, portraits where skin tone is critical are the images that get worked up in both Lightroom and NX2 and then I compare them to see which one I like better. For most images that get this royal treatment, 99 times out of a 100, I prefer the Lightroom version because I have more control and can fine-tune an image far beyond what I can do in NX2. But every so often an image comes out of NX2 looking better than what I was able to get in Lightroom. To be honest, I cannot remember the last time I actually used Nikon Capture NX2. I am running out of excuses with the DNG argument.

    The other reason I don’t convert my image files to DNGs is that I can do so at any time in the future and I don’t feel like Nikon or Adobe is going to ditch any of their raw file formats any time soon. So at some point, if I decide to go the DNG route, I’ll convert everything over and have at least one backup with the original Nikon raw file formats and another hard drive with the DNGs.

    I just wanted to bring up this topic for you the reader as many pros are now using the DNG format, especially many Canon shooters since Digital Photo Pro (DPP), the Canon image processing software, is pretty much horrific and there is no reason not to convert Canon raw images to DNG—especially in light of the fact that Canon has already ditched one raw file format. I am not railing on Canon here. I’m just telling it like it is. If I was a Canon shooter I’d probably be converting all of my images to DNG.

    photo_9Lastly, Adobe also has a stand alone DNG converter that can be used to convert your raw image files to DNG if you don’t want to use Lightroom or Photoshop. You can download the latest DNG converter from Adobe here.

    This blog post is a modified excerpt from my e-book, Adobe Photoshop Lightroom: A Professional Photographer’s Workflow. For more information on this e-book or to purchase the e-book please visit my website.

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