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T
tl_t
Participating Frequently
January 23, 2020
Question

DNG Converter DNG files are 30% larger than Canon compressed CR3 (C-raw) input files

  • January 23, 2020
  • 5 replies
  • 4316 views

Hi, I have a newer Canon camera that uses the .CR3 RAW file format.  You can take your RAW pictures in 2 modes:  full uncompressed CR3, and compressed CR3 (aka, C-raw).  Adobe's official support for CR3 is documented here.  They also support my specific camera, the EOS M6 Mk ii.  

 

Problem:  When I run the Adobe DNG Converter 12.1 (current version) on a compressed CR3 C-raw file, the output DNG file is about 35% larger than the input file.   In contrast, when I use DNG Converter with a full uncompressed CR3, the output DNG file is about 10% smaller than the input file.

 

Why is the DNG Converter producing output files that are larger than compressed CR3 input files? 

 

 

 

 

 

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5 replies

JP Hess
JP Hess
Inspiring
November 6, 2020

Although Adobe touts the benefits of converting to DNG, I rarely do it. When I do, it is more for experimental reasons than anything else. For the most part I leave my images in their original NEF state. I suppose there are arguments for and against either way. There is no right or wrong answer, really. I don't think disk space is really an issue. It's really what ever makes the user feel confident.

 

If you are one who prefers to write metadata to changes in Lightroom, the benefit of the DNG is that there would not be an XMP file. The metadata would be written directly to the DNG file. Personally, I have always just relied on the Lightroom catalog to retain the metadata so I don't have XMP files anyway and I haven't ever regretted it. That's my personal choice. If I ever need an XMP file for an individual image it's easy to create.

 

Added later: my apologies for commenting so much about Lightroom. I forgot that I was in the Camera Raw forum.

    L
    landyiscandy
    Participant
    November 6, 2020

    Hi, I had the same problem and I've discovered something super weird. When I convert the files on import with LR the CR3 files will slightly reduce in size. When I convert the CR3 files to DNG with "Adobe DNG Converter" they increase slightly in size. (Not nearly the 30% size difference, they increase maybe 3% in size.) But I don't understand why, since when I "copy as DNG" in LR on import the files slightly reduce in size.

      JP Hess
      JP Hess
      Inspiring
      January 25, 2020

      There is no performance benefit to having your images on a SSD. There IS some benefit to having Lightroom (the program itself) and the catalog on SSD, but you would do just as well to have the images on a good quality spinning hard drive with reliable backup. The images are not accessed by Lightroom, all action is performed in the catalog.

      T
      tl_tAuthor
      Participating Frequently
      January 25, 2020

      Well kind of.  Yes you CAN run your photos on an HDD or even a NAS, but you will see performance gains by using SSD depending on your applications.  In my case, it's not only Lightroom that's touching the files and SSD.  I have a Canon utility that download images from camera to SSD:  an intensive r/w operation.  Then, and Idrive client that scans the SSD to backup to local NAS, and to cloud (a read operation).  Then in the near future, a Dropbox client that will read the photos on disk and sync to the cloud.  I don't think running on HDD kills your performance or anything, I've run photo apps with the source files on HDD and NAS before, but with applications like these, SSD will give a performance boost. 

       

      One other thing is that Lightroom does access the files:  it stores XMP metadata inside the DNG files themselves if you enable that option in the Preferences (which I do).  

      JP Hess
      JP Hess
      Inspiring
      January 27, 2020

      If you're using apps that access the original files then I suppose having the files on SSD could provide some benefit. I have chosen not to do that, but to rely on the Lightroom catalog. 10 years of experience doing that hasn't disappointed me so I'm not going to change at this point. Cataalog performs very well on the SSD, with images stored on spinning hard drives.

      JP Hess
      JP Hess
      Inspiring
      January 23, 2020

      If saving space is of great concern to you, have you considered using the lossy compression option in the DNG converter? 

       

      The other thing you might consider is adding an external hard drive. They are quite reasonable these days.

      T
      tl_tAuthor
      Participating Frequently
      January 23, 2020

      I've never experimented with the DNG lossy compression, didn't realize that existed until now.  I see it's an option in the converter.

       

      If I use that--to minimize impact on image quality--is it better to use the full uncompressed CR3 file format in the camera, so that the DNG lossy compression is operating on the full set of original bits?

       

      Otherwise, the concern would be I'm running DNG lossy compression on top of the CR3 C-raw lossy compression, possibly impacting image quality more than I'd want to.  I'll experiment both ways and see what happens. 

      TheDigitalDog
      TheDigitalDog
      Inspiring
      January 24, 2020

      Frankly, with the cost of storage space, I see little reason for lossy DNG compression. If your main concern is file size, just leave the CR3’s as is. But there ARE some advantages to DNG over just file size. Case in point:

      https://www.cnet.com/news/adobe-offering-new-reasons-to-get-dng-religion/

      http://digitaldog.net/files/ThePowerofDNG.pdf

      Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"
      JP Hess
      JP Hess
      Inspiring
      January 23, 2020

      The DNG converter works on an algorithm that doesn't take into consideration whether or not the original raw file is compressed or not compressed. The DNG converter simply converts the image based on that algorithm. The size of the resulting file will be what it will be, and it varies from one raw file type to another. Some raw files are reduced by as much as 50% while others are reduced by much less. And, as you have discovered, some raw files will increase in size based on how they were originally constructed. There is nothing wrong with the converter and nothing you can do about it.

      T
      tl_tAuthor
      Participating Frequently
      January 23, 2020

      I wonder if the reason the CR3 C-Raw files come out larger, is that the DNG Converter basically unpacks the RAW bits--including that it DE-compresses them for conversion--and then does NOT RE-compress them since they don't have Canon's proprietary algorithm for the C-RAW compression?  

       

      To put that in simpler terms:  I wonder if DNG converter simply "unzips" the compressed C-Raw file, converts it, and then is unable to "re-zip" the compressed bits?  

       

      None of this is ultimately a make-or-break issue for me.  However, it is slightly inconvenient.  The reason I use the CR3 compressed C-Raw format is to save space, both on my camera card and when I move to my PC.  Using DNG converter basically eliminates the space savings on the PC.  I'll keep using it because I want to convert to DNG standard files, but would be a nice-to-have if DNG converter could somehow convert while maintaining the compression level of the bits. 

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