CR3 vs DNG

No more DNG for me.

[Time for another photogeek blog post!] 

I’ve been using a DLSR camera since 2008 and have been photographing in Raw since 2012, after I finally realized the benefits of camera-raw over jpeg.  In 2012 I also started keeping my entire photo collection in Adobe Lightroom, allowing Ligh​​troom to convert any Raw photos to DNG (‘digital negative’) files at the time of import.  Why?  Because I was convinced by books and bloggers that DNG is The Right Way to store images.  Today, ten years later, I’ve changed my mind.  In this post I explain why.

First, why did I use DNG?  Three main reasons:

  • DNG is an open-source format, while Raw files use a proprietary format specific to the camera manufacturer; thus, DNG files are more likely to be readable decades from now, even if camera manufacturers disappear or their formats are deprecated.
  • DNG files include a built-in integrity check – a checksum or hash that can be used to later verify that the file has not been damaged.
  • DNG files are smaller than the original Raw file because they compress the image data; I always use the lossless compression option, so the size reduction is small but there is no degradation in quality.

Why am I now changing my mind?  Three main reasons:

  • DNG files are now larger than the original Raw file, for me, because switched from Nikon to Canon, using Canon’s proprietary “CRAW” format; although lossy, I’ve been unable to tell the difference in quality (see Note2 below) and the resulting “CR3” files are much smaller than the uncompressed Raw files.  When Adobe Lightroom converts these CR3 files to DNG, it uncompresses the CRAW file and then losslessly compresses the image into the DNG file, and the compression ratio is much smaller. For example, my old (crop-frame) Nikon D500 would produce a 24.6MB Raw file that became a (slightly smaller) 22.6MB DNG file, and my new (full-frame) Canon R5 will produce a 15.6MB CRAW CR3 file that becomes a (much larger) 40.2MB DNG file.
  • DNG files are not accepted by some photography contests that limit the types of post-processing allowed in submitted images and require finalists to upload a Raw file corresponding to the submitted image (example: see the rules for the Wildlife Photographer of the Year); if the Raw file is converted to DNG on import to Lightroom, the Raw file is lost forever and such contests would be out of reach.
  • I now use a separate tool to integrity-check all content in my Lightroom collection, and thus do not need (or use) the built-in integrity feature of DNG files; after all, I want to integrity-check all my images (including jpg, png, tif) and videos (including mp4, m4v) and not just the DNG files.  (Although it would be trivial for Lightroom to incorporate such a feature, it does not!)

And three smaller reasons:

  • DNG files might not be preserving all the metadata information from Raw files, in cases where the Adobe DNG converter is unable (or unwilling) to extract, translate, and record all the metadata from the Raw file.  I’m uncertain the degree to which this is true, or whether any important information is lost, but I hate to lose information.
  • I’m confident in the longevity of Canon or Nikon Raw formats; in the worst case, I could convert all my Raw files to DNG at the time those Raw formats appear to be fading from use.
  • I save time when importing Raw files to Lightroom, because Lightroom no longer needs to convert them all to DNG.  Although this task runs in the background, it does sometimes delay my work.

This choice – DNG or Raw – is a subject of debate in the photography community (see Note1 below).  I reviewed many posts and blogs before making my new choice.  Unfortunately, many of the blog posts arguing against DNG are wrong – at least for people whose workflow centers on Lightroom.   Some seem unaware that Lightroom never writes image updates, and (by default) never writes metadata updates, to the underlying files (whether DNG or any other format); that information remains in the catalog. (My catalog includes thousands of jpg and DNG files and none of them have been touched by Lightroom, despite many edits to the metadata and image content.)  So none of the bloggers’ complaints about the cost (or risk) of updating DNG files make sense to me.

I was curious how Lightroom communicates with external tools – both those from Adobe and those provided by third parties.  Maybe in those circumstances there is an advantage to holding the underlying image as a DNG file?  No – I could never find an example.  When I ask Ligh​​troom to “edit in” another tool like Photoshop or Topaz, Lightroom exports a TIF file, which is edited by the external tool and then imported back to Lightroom as a new TIF image.  (They can be big!  for a 25MB CR3, the resulting TIF ranged from 250MB to 658MB after processing in Photoshop or Topaz.)  I have yet to encounter a case where a DNG file (or a Raw + XMP sidecar file) is used to transport an image from tool to tool.

Should you do the same? Not necessarily. It only became a real option for me because DNG’s benefits no longer apply to me.

Comments and corrections welcome!

Note1. If you want to read more, here are some of the references I explored about DNG vs Raw.  Read them with a critical eye, because some of them are outdated or incorrect in certain details.

  • Adobe’s official comparison.
  • “Lightroom Killer Tips” argues against use of DNG files
  • Tim Grey also argues against use of DNG files
  • A useful comment in Quora
  • A 2014 post from Lightroom Queen – useful but quite outdated.
  • Separately, a 2018 video from Tony Northrup does a nice job describing the advantages of lossy DNG compression, which I’m not interested in using.
  • Upvote this suggestion to encourage Adobe to expand the integrity-check feature beyond DNG files to the entire Lightroom catalog!

Note2. For anyone looking to understand CRAW compression – whether it is lossless or lossy, and whether it causes any image degration, the consensus is that it is indeed lossy but the difference is almost impossible to notice.  See for example:

  • Petapixel concluded there are no downsides to CRAW.
  • Nando Harmsen (fStoppers) did detailed quality comparisons and could not find a noticeable difference.
  • “The Digital Picture” blog claims that RAW files are already somewhat compressed, and CRAW are further compressed, indeed, claims “Canon has advised us that the new C-RAW format uses a lossy-compression algorithm,” but with no citation or link.  It went on to do experimental comparisons and concluded the differences are barely noticeable. And: “After repeatedly asking Canon, the only C-RAW downside shared with me is that there may potentially be more noise in shadows when increasing brightness during post processing.”
  • Jan Wegener explains it all in detail, with experiments.  He saw almost no difference, except maybe where deep shadows needed to be pulled.
  • John Ellis explained in it a LR-Queen forum thread.

Author: dfkotz

David Kotz is an outdoor enthusiast, traveller, husband, and father of three. He is also a Professor of Computer Science at Dartmouth College.

4 thoughts on “CR3 vs DNG”

  1. I shoot on Fuji, and I’ve stayed away from DNG for various reasons including a few you’ve listed here. However, you can choose to store the original RAW file inside the DNG for later extraction if needed. This produces a much larger DNG file, but it also gives you all of the benefit (or lack thereof) of the DNG format while still preserving the original RAW. With 32 and 50 TB drives on the horizon, I can’t see any reason to worry about space unless you’re storing (and trust) the cloud with specific overpriced providers.

    1. Thanks. I considered embedded Raw back in 2012 and again now in 2022. Not for me, because (a) I don’t think the contest organizers who demand a Raw file would find that approach acceptable, and (b) I do worry about space because I store my collection in the cloud. Yes, I could buy more space, but I don’t see a benefit to storing a 56MB DNG+RAW file instead of a 16MB CR3 file. That triples (or more) my space costs without much benefit.

  2. Hi David! Excellent post! I actually found your blog from a comment you made on Validator LR Plugin’s blog where you said: “…Of course I discovered it only after writing my own tool, which has very similar behavior but runs strictly as a command-line bash script…” You mention this tool also in the current post. I wonder I that something you would like to share, as it seems very useful?

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