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DNG vs. ARW?

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rovhazman View Drop Down
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Post Options Post Options   Quote rovhazman Quote  Post ReplyReply Direct Link To This Post Topic: DNG vs. ARW?
    Posted: 05 July 2009 at 19:38
Sorry if it was asked before.

I am considering to start to keep all my RAW files as DNG rather than ARW. Mainly because in DNG you don't have sidecar files.

However, I wonder if there is information lost in the processes of converting the ARW to DNG. For example, the ARW contain information about the lens which Adobe cannot read - is this information stays in the DNG file?
 



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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2009 at 20:32
I don't know if anything is lost, but out of principle I would keep the original ARW/MRW. If you run out of space just burn them on a CD or DVD and store in a safe place. Better be safe then sorry I would think.
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Post Options Post Options   Quote kevinbm Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2009 at 20:35
Seems like a needless extra step to me to convert to DNG unless you are using Photoshop 2 or below whose version of Camera Raw can't read ARW files from the A700
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rovhazman View Drop Down
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Post Options Post Options   Quote rovhazman Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2009 at 20:40
Thanks for the replies.

If there is doubt I'll stay with the ARW. However, lately I backuped my RAW files and I realized that I lost all the processing I already did. I know that there are smarter ways for backup without losing the processing, but I thought working with DNG can solve it.
I am working with LR so I can convert the files while importing them - no extra step.
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Post Options Post Options   Quote CronoDL Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2009 at 00:02
Since you're using Lightroom, you shouldn't need to worry about sidecar files. Lightroom stores everything inside its catalog, and won't generate sidecars unless you tell it to.

I keep my RAWs as ARWs. I don't find much of an advantage to using DNG, mainly because I use Lightroom for organizing, tagging, IPTC, etc. If I didn't use LR, I can see how the xmp file can become one more thing to keep track of.
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Post Options Post Options   Quote Vivec Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2009 at 01:07
A while ago, I was converting from ARW to DNG files since I liked the idea of a standard format. However, I found out that the dng conversion wasn't entirely lossless as the Sony metadata got lost -- in particular, the lens id is not preserved and one can no longer use programs like alphalensinfo to identify the lenses
note: the turns out the real story is more subtle -- see later in this thread

So, nowadays I just use ARW files. Also, I am a lot less worried about the file format becoming obsolete: first of all, there are excellent raw conversion tools that are in the public domain as ANSI C which will always work, and I can hardly imagine Adobe dropping support for raw conversion without giving a upgrade solution. Finally, since I wrote the alphalensinfo tool I now have more insight in the raw file format of Sony and it is a very straight forward TIFF file so it would be easy to support in the future if necessary.

Edited by Vivec - 20 July 2009 at 09:04
 



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Post Options Post Options   Quote polyglot Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2009 at 03:25
DNG is good because it's an open format, but the conversion to DNG will (probably) lose some details - see Vivec's post. Not a lot of point in doing the conversion even if we would maybe prefer that Sony produced DNGs directly. Honestly it doesn't really matter as long as they don't do crazy stuff like encrypted-raw to lock us into using proprietary software - that sort of thing would definitely make ARWs non-archival.

Just don't forget to also backup the sidecar-files (eg. .ufraw, .xmp, etc) or your lightroom catalogue!
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Post Options Post Options   Quote rovhazman Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2009 at 06:25
Thanks everyone!
Vivec, you abswered my question. I'll keep the ARW files (and maybe use the DNG for backup the original files, after the lensid is embedded).
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Post Options Post Options   Quote Vivec Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2009 at 06:34
Originally posted by rovhazman rovhazman wrote:

Thanks everyone!
Vivec, you abswered my question. I'll keep the ARW files (and maybe use the DNG for backup the original files, after the lensid is embedded).


One thing you can do is use alphalensinfo on the original ARW file to generate an XMP file and then convert the ARW file to a DNG. Still, since the Sony "maker note" is discarded, there might be other meta information that is lost.
note: it turns out the real story is more subtle -- see later in this thread

Just to be clear, according to Adobe there should not be any loss of image quality when converting to DNG, i.e. supposedly all image data is preserved. I am just talking about Sony specific meta data.

Edited by Vivec - 20 July 2009 at 09:04
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 08 July 2009 at 14:12
At first blush storing the xmp info in the DNG file seems a good idea. However when you use a back-up program that only updates "changed files" (I have one of those and use it to make back-ups on external hard drives) it's much quicker backing up 4 or 5 kb xmp file updates vs. whole 9-30 MB DNG file updates (size depending on camera used).

So even w/o the problem pointed out by Vivec having small xmp files is not such a bad idea.
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Post Options Post Options   Quote rovhazman Quote  Post ReplyReply Direct Link To This Post Posted: 08 July 2009 at 14:43
Thanks again.

So that is what I am doing - on my working HD (external) I am keeping the ARW files. On my backup HD (external) I am saving them as DNG (after doing all the editing and adding lens id). Just to be sure that I'll have the support for ever (although I think Adobe will disappear before Sony will...).

I also have un-processed JPEG copy on my local HD (I am shooting JPEG+cRAW), but I am not sure I am going to keep it. It is nice to have all the pictures on the computer, but the HD is getting full. So maybe I'll start shooting RAW only and save JPEGs of the selected pictures only.
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 08 July 2009 at 15:17
My workflow is actually a bit different:

I store all working MRW + ARW + XMP files on my internal hard drive.
Once a week I back up my entire raw file directory to an external hard drive, using the option "update changed files only".

In that way I have a back up with all the recent edits, even for files I shot 1 or 2 years ago and worked on the past week. This goes quite quickly since for the back-up of the edits the program only has to copy the updated xmp's, since the ARW/MRW's never change. Only new ARW/MRW's from that week have to get copied entirely. So if I would have converted everything to DNG's it would need much more time to back-up the much bigger files in case changes have been made to older files.

I still make a backup to DNG once or twice a year and burn those on DVD, but never re-back them up in case additional PP has taken place. That's kind of a "last resort" backup that has never been used yet.
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Post Options Post Options   Quote rovhazman Quote  Post ReplyReply Direct Link To This Post Posted: 09 July 2009 at 03:59
pegelli - I am going to adopt your workflow - it makes much more sense. I hope I am not getting troubles with copyright...
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Post Options Post Options   Quote polyglot Quote  Post ReplyReply Direct Link To This Post Posted: 09 July 2009 at 04:41
pegelli: why bother with DNG in your annual DVD-burning session? Why not just burn the ARW+XMP files?

PS: please always use par2 on optical media intended for long-term storage.
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