FAQ: Canon DPP & CR2
Note: All writting is based on my personal experience.
Canon DPP related comments are ment for DPP v188.8.131.52 (unless otherwise noted).
How safe it is to modify metadata inside Canon CR2 raw files?Usually, you'll get simple advice: "don't touch raw file!" -in most cases from those, who didn't bother to get familiar with metadata, had bad experience with some tool or simply don't know what they are doing.
Do you dare to change metadata (exif, for example) inside JPG or TIF file? Yes? You see, CR2 is the same thing: Canon CR2 file is TIF format actually -no secrets in this regard. Of course, one must distinguish between metadata and raw image data. Both reside inside CR2 file and while you can (almost) freely modify metadata, you shouldn't (and usually can't) modify raw image data.
So, when talking about "how safe" is modifying CR2 metadata, you can also ask: how safe is modifying metadata inside JPG file?
Many are afraid, their CR2 files may not be readable by DPP (or some other tool) anymore, after metadata has been modified. This is a valid point, but the same can be true for JPG files too -in both cases, this apply only if metadata is damaged!
To answer the question: using ExifTool(GUI), it is totally safe to modify/write "public" metadata inside CR2 files.
Warning: Modifying MakerNotes metadata section is not recommened -unless you really know what are you trying to accomplish.
As powerfull as ExifTool is, it makes it possible to modify Canon MakerNotes tags too. To avoid damage made by user, ExifToolGUI is restricted to modify only two tags there: OwnerName and LensType -both are very safe to modify.
Why modifying metadata inside CR2 files at all?Well, you wouldn't read that, if you don't know the answer yet. Anyway, here it goes...
Looking inside exif, you can see when photo was taken (was yor camera DateTime settings correct?), but you can't see where it was taken -this is the most obvious example. And you'd like to add some your personal notices about photo: who's on it, was tripod used, did you allready make a print (for album), who took the photo,...
OK, you use some XXX photo cataloging software, where you can write such things, which is then saved into database. Then you realize, software you use isn't good enough for your needs or simply some better YYY cataloging software became available... I think you know where this leads: how to transfer all your personal notices from XXX into YYY database? Even there may be some solution (from YYY creator), you will usually lose something. In worst case, you'll need to tag your photos from beginning on.
Now, if your notices are written directly into image files, you never need take care of where your notices are. And all you have to do is: import your images -and all your personal data (locations, keywords, notices...) will be automatically imported too.
How does Canon DPP handle (modified) metadata?As expected: DPP only read Exif (incl. MakerNotes) section and doesn't bother if there's more (IPTC or XMP) data inside CR2.
Even one would think DPP doesn't care about IPTC/XMP at all, this isn't totally true. You can see that, when you convert CR2 file:
-for the first time, implemented in DPP v184.108.40.206, all metadata is copied into converted file.
Why would someone replace existing embedded JPG image inside CR2?Beside metadata and raw image data, every CR2 file also contains embedded JPG image. It is automatically generated by camera and serves for fast preview on camera screen (btw. to gain speed, most image viewers show embedded JPG too). In short: embedded JPG shows how would photo look alike, if shot would be taken in JPG mode. The only difference is it's size: usually, embedded JPG has relative small resolution (I said "usually" -because this depends on camera model and it's settings).
As said, most viewers use embedded JPG for previewing and so does most cataloging software. Now, there may be few things, which can bother us... for example:
The only thing you loose by replacing embedded JPG, is... original embedded image. Big deal -it was not usefull anyway (otherwise there would be no need to replace it). Most photos are usually printed on 4x6" (10x15cm) paper. So, for photo quality printing (about 300ppi), we need to embed JPG image which size is 1800x1200 pixels (horizontal orientation).
How does DPP react after replacement of existing embedded JPG image? DPP doesn't use embedded JPG at all, so nothing changes in this regard.
Don't get me wrong: I'm not saying one should replace embedded previews in all CR2 files. I'm just saying it may be needed and that it is possible to accomplish that. Still suspicious? Let me ask: would you use this option, if it would be possible within DPP? I bet you would.
How about converting to DNG?This is always personal decission... anyway, here's my opinion:
From above, one might think I "hate" DNG. Not really. It's just, I don't see any reason for jumping into it right now (June, 2008).