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Antoine HLMN
Antoine HLMN
Inspiring
June 5, 2026
Question

Convert to DNG increases file size

  • June 5, 2026
  • 2 replies
  • 47 views

I tried the “convert to DNG” function and in INCREASED the file size. Settings were:

  • Only convert Raw files (obviously)
  • Delete originals after successful conversion
  • Extension: dng
  • Compatibility: CR 16.0 and later
  • JPEG Preview: None
  • Emebed fast load data: NO
  • Use Lossy compression: NO
  • Embed Original Raw File: NO

While I do understand the benefit of DNG over proprietary raw, for long term support, I do not think it’s a good idea to allow an increase in file size without a warning.

While the alleged open character of the dng format is a good selling point, I do not think it’s going to be an issue to open raw files in the future. Nevertheless, I appreciate that option. Therefore I think the main selling point of dng would be a higher compression yielding in smaller files.

Note: I also know that a Lossy compression would obviously output smaller files, but that’s not the point.

 

    2 replies

    JohanElzenga
    Community Expert
    JohanElzengaCommunity Expert
    Community Expert
    June 5, 2026

    Without you saying what the original raw file was (raw files are often compressed these days), nobody can say if the bigger size of a non-compressed DNG version is strange or completely as expected.

    -- Johan W. Elzenga
    R
    Community Expert
    richardplondonCommunity Expert
    Community Expert
    June 5, 2026

    Another consideration is that sometimes a Raw converter is available which includes some supposed “special sauce” from the camera manufacturer - which may simply amount to, the ability to match specific in-camera picture modes as would otherwise have been applied to JPG output. So that is a point of comparison with converting through generalised Adobe processing. This dedicated Raw converter will accept an out of camera Raw file (from that manufacturer) but may not accept a converted DNG. Converting to DNG is one-way and irretrievable unless an entire duplicate of the out of camera Raw file is extractably embedded.

     

    Given that my preferred converter (LrC) is for now equally happy to take in a camera original Raw as a DNG, I’ve till now been reluctant to commit such a conversion. If the proprietary file format was going to no longer be supported, but DNG was: only that would be the sort of necessity which dictates it.

     

    BTW the separate sidecar file into which metadata is written when the Raw is proprietary: I actively prefer that it is non-embedded. This way the camera file remains always untouched, and if some edits have been written out meanwhile: my next refresh of file backup is now copying just those few changed Kb per each updated photo - not, writing an entire DNG file again for each.

      Antoine HLMN
      Antoine HLMNAuthor
      Inspiring
      June 5, 2026

      Exactly my point 👍🏻

       

      While Adobe’s reps might disagree, converting to dng ends up dumbing down the file by loosing all the feature you have mentioned. The argument of future proofing the files doesn’t really hold up as modern os have no issues whatsoever to read raw files. But they have a point and if raw files could be standardised, or be dng files, that’d be great. (By the way, I wonder if Adobe charges manufacturers which include dng as options (Pentax, Sigma, …))


      Long story short: imho, the main benefit of dng is file size reduction (being lossy or lossless) and an increase in file size (without warning) is a big no no.

      R
      Community Expert
      richardplondonCommunity Expert
      Community Expert
      June 5, 2026

      That’s an interesting one about e.g. Pentax (I have one): the native DNG was fully supported as an alternative to PEF within the Pentax supplied Raw converter, when I tried this several years ago, but an Adobe converted DNG (derived from a PEF) was not. Assuming one cares about such things of course. At one stage Lightroom(C) supported PEF properly but Pentax native DNG only under generic compatibility. Believe that one was later fixed.

       

      Those who know likely cannot say what negotiations may happen behind the scenes around DNG!  

       

      I have often seen the embedding of metadata by DNG presented as a positive advantage, but remain unconvinced.

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