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Adobe DNG Converter: Possible Loss of Metadata, Guaranteed Loss of File Dates, but Space Savings for Uncompressed RAW

re: botched design
re: Adobe DNG Converter

Adobe DNG Converter can convert virtually any raw file to a DNG, the format most likely to be supported 20 or 50 years from now, though given the billions of ARW, CR2/3, NEF, etc files, it seems unlikely for those formats to ever be an issue.

Unlike most manufacturer-specific raw formats, the Digital Negative is an openly published specification that not only is supported by Adobe, but is also freely available for other software and hardware vendors to support. Consequently, it can be a safer file format to use for long-term archival purposes. Archiving your file as a digital negative eliminates worries that the raw file will no longer be readable once the camera format that created it becomes obsolete...

I’m not buying the claims of “no longer readable”. There are billions of NEF, CR2, CR3 etc files around, and support for them will not end.

Barring lack of file format support, there is zero raw-conversion advantage in Lightroom or Photoshop or any other raw converter to using DNG. Zero. Keep your original capture, unaltered! Unless...

Benefits of DNG — compression for space savings

Do you want to backup 8TB instead of 4TB? Spend $4000 instead of $2000 for the same functionality? See the Sony workflow tax, ditto for Hasselblad X2D.

The only good reason to convert to DNG is for space savings.

That is, when huge uncompressed raw files are needlessly foisted on you, wasting huge amounts of space on main drive and backups. Converting such huge files to DNG and saving 50% or more on space (lossless compression) is very worthwhile. Your wallet will thank you and you will spend less time backing up, half the time on data validation, etc.

Issues with DNG conversion

Conversion to DNG is not without issues.

Loss of file capture dates

I often sort by capture date; it is a key external attribute(metadata) of the capture. The loss of file capture dates is unacceptable; I consider this such an egregious issue that I call it a BUG.

If I have multiple _DGL0037.ARW files, it matters if one was shot in 2017, and another in 2018, and 5 others on different dates—I want those dates. Destroying dates is unacceptable.

I have asked Adobe to add an option to preserve file dates.

The dates are not totally lost, since they are in the EXIF information in the DNG. But having to manually run exiftool to extract and set dates is a burden and hassle, and horribly confusing even for nerds like me, even if you don’t get error messages (I did) and put up with the glacial speed—unacceptable. Not for the faint-hearted.

I wrote my own tool for fixing the dates, and some other issues, one that is a lot less capable, but trivially easy to use (eg "img fix-dates <images>"). Point is, it should not be necessary to fix this problem in the first place!

Loss of capture dates after conversion to DNG by Adobe DNG Converter

New backups, wasted time

First, converting to DNG is usually and only a waste of your time. And you will have to make a fresh backup to backup the DNG files, and after throwing away the previous raw files.

Far worse, unless you lock the DNG files or ensure they are not changed by configuring Adobe software to use sidecar XMP files (only), DNG is modified when edited*—a huge headache for data verification and backups.

That is, instead of changing 2K of metadata in an XMP file, a huge raw file is changed, making for lengthy backups. And the dreaded “Time Machine disk is full” headache, since with each change, you’ll get a fresh copy of that 50MB or 100MB raw file.

DNG usually incompatible with proprietary camera software

Convert your Sony uncompressed raw ARW files to DNG for a ~50% space savings? Oops—the Sony software doesn’t work with DNG. Bye-bye pixel shift unless you do it first with the ARW files. Ditto for ARQ files.

In general, most camera manufacturer software will work only with their own raw file format. If you have any feature at all that you want from that software, conversion to DNG is a bad idea.

* Metadata is written into the DNG, thus marking the file as changed. The entire file will be marked for backup and often change in size too.

Loss of metadata?

Comments from Adobe engineering:

Regarding metadata, I understand your hesitation.  Our general policy is to include all the proprietary metadata (that we know about) when converting non-DNG raw files to DNG (*). 

For example, we include Canon, Nikon, and Sony MakerNote data when converting from CR2/CR3/NEF/ARW/ARQ to DNG.  However, since this information is vendor-proprietary, it is impossible for us to be 100% certain that the converted DNG contains all the private metadata.  It is always possible that there is private metadata elsewhere in the file, that we just don’t know about.  I don’t have an easy answer to this. 

(*) Note, only when creating DNGs that are lossless compressed or uncompressed.  If one chooses the lossy compression option when converting to DNG, then we assume the goal is to save (a lot more) space and that one is not really aiming for the highest-quality results, so we deliberately exclude the private MakerNotes from lossy-compressed DNGs.

DIGLLOYD: I feel more comfortable now in converting to DNG for good reasons, eg Sony uncompressed raw files. However, the loss of file dates is unacceptable—I need that fixed; I am not keen on having to manually run exiftool to extract and set dates.

Not sure why anyone would want a lossy-compressed DNG other than saving space. I suppose it is better than a JPEG (maybe).

Anon reader writes:

“Barring lack of file format support, there is zero raw-conversion advantage in Lightroom or Photoshop or any other raw converter to using DNG. Zero.” 

Not true. If you have, for example, a version of Lightroom or PS CS6 that refuses to read a raw image because the camera is unsupported (typically too new), by converting the image to DNG you can edit it.   I refuse to pay Adobe CC tax and continue to use Lightroom 6 which is fine for my needs. My Canon EOS M6 II camera is not supported by LR6 but by converting it to DNG I can happily edit it, keeping the original .CR3 file in a backup. 

DIGLLOYD: the two movies on one screen thing... obliviousness to direct evidence right in front of one’s eyes... sigh. There, in a nutshell, is captured the core issue with public discourse today, or rather, its utter breakdown. I almost left that predicate out, as it’s tiresome to have to spell out obvious things. I thought I had innoculated myself by keeping it... doh!

The only “tax” involved here is wasting time. Strikingly, such comments demonstrate a further lack of awareness that no value has any meaning without comparing it to something, eg a $10 a month fee vs the value of one’s time. All too often this plagues many #artists (those untrained in any technical discipline which involves logica and proper comparison). Similarly, people bitch about $10 a month when their phone bills are $100 or more (mine is $265 for 7 devices).

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