Validating RAW files - DPChallenge Forums

Olympus 8mm f/1.8 M.Zuiko Digital ED Fisheye PRO Lens

02/14/2011 03:08:05 PM · #1

I tried to slip this in under

cutout's thread about his DQ problems, but the hijack didn't work, so I'll have to start my own thread and hopefully will get an answer.

I have always (apparently mistakenly) understood that RAW files cannot be modified. Yet in Lightroom, which I have been running as a trial, images to which I have added keywords show Metadata status as "Has been changed". When I look at the EXIF data of the same files in Bridge there may be a variation of about one second between date created and date modified. Under the file properties in Windows Explorer it shows the file as being created at the time it was downloaded to the computer, and having been modified at the (earlier) time when the photo was taken. All of this seems rather confusing and I'm getting worried that if one of my photos needs validation, the RAW may prove not to be acceptable.

After posting that paragraph I noticed that in Bridge one of my files shows date modified as the day after it was created while others from the same sequence have a variation of no more than a second. I don't understand how this can happen as I didn't add keywords until at least a month later. I have no clue how I could have modified the RAW at that stage.

Originally I thought that the issue may have been related to Lightroom, which I probably won't buy, as I'm considering rather upgrading Photoshop from Elements 7 to CS5. However the file I found with modified date showed a modification date about a month before I installed Lightroom, so I'm stumped as to how the modification occurred. I really want to find out what has gone wrong here before it affects one of my challenge entries, just in case I ever manage to get a good score again.

RainMotorsports

Nikon D60

Nikon AF-S DX Zoom-Nikkor 18-55mm f/3.5-5.6G VR

02/14/2011 03:13:16 PM · #2

Any file of any kind can be modified in some way shape or form. Though messing with a raw files actually picture information isn't the case here nor is it directly of any good value. Transfer and software that adjust values like white balance (manufacturers software usually) are the normal culprits.

Just copy the file from the camera to a folder, work from a copy of that at all times. That way you have a real original never viewed by any software that could mess with it. I keep two copies of all originals a working and a master. Takes up alot of space though.

Olympus 8mm f/1.8 M.Zuiko Digital ED Fisheye PRO Lens

02/14/2011 03:26:12 PM · #3

I think when I got my new camera I used the camera software to download one lot of photos but was immediately suspicious that something was wrong, so I have gone back to the normal cut and paste. I thought once I started shooting RAW that I wouldn't have to worry about keeping two copies of everything, but I suppose I'll have to do it. Space is going to be a problem, but I'll have to manage somehow.

I wish I knew how that one file got modified though because I'm sure I didn't do anything strange to it.

02/14/2011 03:52:12 PM · #4

At present, there is no publicly available tool that will allow someone to edit the image data in a RAW file. It is theoretically possible, it's just that no current tools work this way. Keep in mind that RAW data is really not image data in the strictest sense, it's just a numerical representation of brightness levels for individual pixels. In order to create an actual image, the data first needs to be "demosaiced" in order to re-create the two missing color channels for each pixel location. Note that this does not apply to the Foveon sensors used by Sigma.
So AFAIK, unless something has changed since I left the SC, a RAW file is still a much more robust proof file than a JPEG. The "modified date" has no impact with a RAW file, other than as an indication of when the file was last accessed.
Some tools do modify the metadata in the RAW file, saving changes to white balance, exposure, etc.; these changes also do not affect the validity of a RAW file, since the underlying data is not changed.
One final note; converting a RAW file to DNG essentially places it in the same category as a JPEG file for proof purposes, because the DNG format can contain demosaiced, edited data.

Olympus 8mm f/1.8 M.Zuiko Digital ED Fisheye PRO Lens

02/14/2011 04:01:11 PM · #5

A few of my early photos from my 7D were converted to DNG because Elements wouldn't read the CR2 files, but I updated my version of Camera Raw, so that isn't an issue. If "modified date" doesn't affect validity of a challenge entry, then I don't really care what date the programs show. But it does seem a bit strange that different programs seem to show different information for the same files.

02/14/2011 04:05:45 PM · #6

Originally posted by GinaRothfels:

...But it does seem a bit strange that different programs seem to show different information for the same files.

It's very possible that one program is just reporting the "last modified" date stored by the operating system (something that is not even a part of the file, but information that is stored separately) while the other program is actually looking to the metadata within the file for that information.

Olympus 8mm f/1.8 M.Zuiko Digital ED Fisheye PRO Lens

02/14/2011 04:12:32 PM · #7

Thanks. It sounds like I'm looking for trouble where there really isn't a problem. I think it was the keywords in Lightroom that first got me worried. But it's unlikely I'll even buy Lightroom (as my only interest in it was as the cheapest way to use Nik's HDR program), so that issue will disappear when my Lighroom trial expires in about an hour anyway.

RainMotorsports

Nikon D60

Nikon AF-S DX Zoom-Nikkor 18-55mm f/3.5-5.6G VR

02/15/2011 12:52:56 AM · #8

Originally posted by kirbic:

Some tools do modify the metadata in the RAW file, saving changes to white balance, exposure, etc.; these changes also do not affect the validity of a RAW file, since the underlying data is not changed.

Arw you sure? Because I seem to remember in cutout's case (though a jpeg) they pointed to the exact same Modified/Created exif date that gets modified by nikon software. Im 100% it does it on the transfer we all know that. Never looked but I am 99% sure it changes that modified date in the raw's exif and that DPC doesnt consider that valid despite the facts.

spiritualspatula

Panasonic LUMIX DMC-LX100

Nikon AF-S NIKKOR 24-70mm f/2.8G ED

02/15/2011 02:59:48 AM · #9

Originally posted by kirbic:

Capture NX allows you to open and resave a Nikon NEF file, as an NEF format. Wouldn't this be "altering a RAW?"

bvy

Sigma DP1x

02/15/2011 07:29:31 AM · #10

Originally posted by kirbic:

In order to create an actual image, the data first needs to be "demosaiced" in order to re-create the two missing color channels for each pixel location. Note that this does not apply to the Foveon sensors used by Sigma.

Thank you for that disclaimer. I'm hoping the SD1 will be a game changer. (Sorry for the digression.)

02/15/2011 07:35:06 AM · #11

Originally posted by RainMotorsports:

Originally posted by kirbic:
Some tools do modify the metadata in the RAW file, saving changes to white balance, exposure, etc.; these changes also do not affect the validity of a RAW file, since the underlying data is not changed.

Arw you sure? Because I seem to remember in cutout's case (though a jpeg) they pointed to the exact same Modified/Created exif date that gets modified by nikon software. Im 100% it does it on the transfer we all know that. Never looked but I am 99% sure it changes that modified date in the raw's exif and that DPC doesnt consider that valid despite the facts.

Yes, at this point I am sure. I won't say more about the nuts and bolts of assessing validity of RAW files, but suffice to say that I'm not aware of any disqualification for inadvertent modification of a RAW file's metadata or image data.