Any disadvantages when saving in DNG format? vs CR2 or NEF

[cyber3d]

There are a number of threads on the forum regarding RAW vs whatever. But, are there any arguments to not use DNG?

I find myself in a quandary. I need to start using a format that both Aperture and Photoshop can use with the least amount of hassle and degradation.

[Doug Sundseth]

I've neither experienced nor heard of any disadvantages to DNG files. (I've been using them for quite a while now.)

[Doug Pardee]

There are a number of arguments against using DNG, but many of them come down to, "why add yet another step to the workflow?" Which has its own answer for some people and not for others.

If you convert to DNG, you need to make a decision: keep the Raw files too, or discard them? One of the features of DNG is that everything is stored in a single file. One of the hazards of DNG is that everything is stored in a single file. The DNG file must be re-written whenever any change is made at all. A software bug or a power glitch at the wrong instant could destroy the DNG file. Most (but not all) Raw editors never rewrite the Raw file, so that file is relatively safe.

A (minor) consideration is that the DNG format keeps going through revisions. We're up to DNG 1.3 now, but most software currently doesn't understand 1.3 and treats it as 1.1 or 1.2. Which, to be fair, the DNG revision process is designed to permit. A DNG 1.3 file is usable as DNG 1.3 on software that understands it, or as DNG 1.0 on really primitive software. The nuisance is that if you have, say, some DNG 1.1 files, a Raw converter that does understand DNG 1.3 will not be able to take advantage of the newer features. Again, to be fair, most Raw converters ignore all of that stuff if they know how to convert Raw files from the camera in question, so about the only time it really matters is with Raw converters that otherwise couldn't process your Raw files.

For cameras with non-standard sensor designs — basically Sigma's Foveon and in some cases Fuji — the Raw file has to be converted to a "linear DNG", which is sub-optimal.

Something that's pretty much become a non-concern: whether Adobe is committed to DNG, or going to shove it overboard like it did JPEG 2000. Adobe hasn't made any indications of backing away from DNG, and most Raw converters process DNG.

Which brings up what's probably the biggest concern about DNG: not all Raw converters will process it. In particular, Raw converters provided by the camera manufacturer don't, and often those products provide some of the best Raw conversions available for a particular camera model. By going DNG, you're cutting yourself off from them, and from DNG-holdouts like Bibble and DxO. See http://www.barrypearson.co.uk/articles/dng/not_yet.htm for a listing. In practice, most people considering DNG are totally committed to Adobe software, so this probably isn't such a big deal.

[inkista]

Theoretically, another disadvantage to going with DNG is that metadata that the manufacturer comes up with that isn't part of the DNG standard is discarded. Things that are model-specific, like in-camera lens correction, etc. may be dropped. This is why DNG gives you the option of embedding the original RAW file, if you want to use the camera manufacturer's RAW converter later on down the line, but it will effectively double the size of the file.

[Dee Lund]

I am relatively new to the DNG format and have not discovered any disadvantages. When I started using DNG I was nervous as from past experience something new is not necessarily something good! To play safe I keep a copy of the CR2 files on a portable hard drive, that way I can work with the image in DNG but I know I have the CR2 file if anything should go wrong. Hope this helps.

[Doug Pardee]

Originally Posted by inkista

Theoretically, another disadvantage to going with DNG is that metadata that the manufacturer comes up with that isn't part of the DNG standard is discarded. Things that are model-specific, like in-camera lens correction, etc. may be dropped. This is why DNG gives you the option of embedding the original RAW file, if you want to use the camera manufacturer's RAW converter later on down the line, but it will effectively double the size of the file.

From the beginning, the DNG specification has allowed for the storage of "maker notes" in a field called DNGPrivateData. From almost the beginning (version 3.1 back in May 2005), Adobe's DNG converters have copied the maker notes into that DNG field for most cameras. Specifically:

DNG Converter 3.1 and above does indeed move all EXIF private maker note from all TIFF-EP based raw file formats, not just NEF and CR2 files. The file formats that do NOT use EXIF based private maker notes are not migrated. File formats from; Kodak, Foveon and Leaf do not use EXIF private maker notes, so those files are not supported for migration. Additionally, Canon CRW files and Fuji RAF do not completely adhear to the TIFF-EP and EXIF spec. So some metadata will be migrated and some will be stripped.

(ref: PhotoshopNews: Photoshop News and Information Archive DNG Workflow / Part I)

However, that doesn't mean that software that processes DNG files will necessarily utilize those maker notes, and it doesn't mean that the copied maker notes are even usable to begin with. It's generally believed that there are no usability problems with maker notes copied from CR2 and NEF files, but it's possible that some camera models have encoded the maker notes with the assumption that the maker notes and/or other data are located at specific offsets within the file.

DNG has a field called MakerNoteSafety that can be used to indicate that the data in the DNGPrivateData field is unreliable because of one or more of the usability issues. I don't know if the Adobe DNG Converter software sets that flag or not. I suspect not — that it's basically there for camera manufacturers to use.

See also: http://www.barrypearson.co.uk/articl...dngprivatedata


Re in-camera lens correction: the DNG 1.3 specification provides "opcode lists" to specify post-demosaicing image processing, including lens correction. To my knowledge, DNG 1.3 isn't widely supported yet by Raw converters, and any files already converted into an earlier version of DNG would need to be re-converted into DNG 1.3. I also don't know to what extent Adobe's DNG Converter currently supports generation of opcode lists for camera models with in-camera lens correction.

All of this points to one of the weaknesses of DNG in practice: the capabilities may be there, but whether the implementations exist is a different matter, and it's a matter that oftentimes is impossible to determine.

[Doug Sundseth]

Note that if you're using Lightroom, you can convert to DNG and import and save a second file for backup at the same time. The second file is the original RAW file, not a DNG.

[Doug Pardee]

I think there's an unstated question in there about whether DNG is a good idea or not. I personally don't use DNG, but in about seven years of watching a number of photography forum boards, I've never seen anyone say that they regretted using DNG or regretted not using DNG. It seems to be a matter of personal taste rather than technical issues.

Nikon owners seem more likely to be happy DNG users, primarily because the DNG lossless compression results in significantly smaller files than ordinary NEF Raw — I believe that the DNG file size is about the same as NEF lossless-compressed Raw. Obviously (?) this doesn't work if you keep the NEF file on your hard drive, either separately or stored inside the DNG file, because then you've got more disk space dedicated to holding your Raw data. You'll need to either move the NEF file off onto a backup medium or discard it altogether. From what I've seen, most of the happy Nikon DNG users discard their NEFs, thereby fully committing to DNG with no way to ever go back.

Then there are some people who hate XMP sidecar files, and almost certainly would be happier using DNG where all of the data is kept in one file.

[cyber3d]

I may have a solution in that we may dump using Aperture and use only Photoshop. I scream "Yeah!" under my breath!

Now, the other problem is the logistics of sharing a "master" images drive via airport (since the machines are separated by some distance and cables are not in the equation).

I figure we have 2 partitions. One for the RAW files, another for the finished PSD edited files.

In Bridge, each local machine will have a favorites showing:
1. the "airported" Master partition (untouched RAW files)
2. the "airported" Finished partition (Edited PSD files)


a) "download" a master to local hard drive, do edits and rename with version number.
b) "upload" the final version to the airport drive in the "finished" partition in a folder.

If someone needs to do any tweaking they can grab the latest "final" edited version, download to their local drive and tweak away. Once done, upload it back with a revision number.


Does that sound reasonable? Any thoughts? Comments?

May be I should start a new thread....
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