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ngarefalosjr
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Artifacts in DNG files converted from NEF

Jan 21, 2012 12:05 PM

On two occasions, I've encountered artifacts in my photos that I've converted from NEF (using Nikon D7000) to DNG format in Lightroom 3.6.  Is there a "fix" for this?  

 
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    Jan 21, 2012 12:13 PM   in reply to ngarefalosjr

    What kind of artifacts? A screen shot might help. There shouldn't be any.

     

    Hal

     
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    Jan 21, 2012 12:51 PM   in reply to ngarefalosjr

    That's a corrupted image. When you export the DNG to a JPEG on your hard drive, is the resulting file also containing that blemish? If so, then the DNG is corrupt. If not, it's your preview that's corrupt.

     

    Did you convert the files to DNG on import, or did you do it afterwards?

     

    Hal

     
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    Jan 21, 2012 4:15 PM   in reply to ngarefalosjr

    Probably not. It's the same process.

     

    Late-model DNGs contain a checksum that alerts Adobe programs if they go corrupt after they were created, and your files don't do that. If they did, you'd get an error message when you tried to us the DNG. That says to me that either the original raw file was corrupt or that the corruption happened during the creation process. Do you still have the original?

     

    Hal

     
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    Jan 22, 2012 5:58 AM   in reply to ngarefalosjr

    So try importing the original file (without converting to DNG). Does it have the same blemish when viewed in Lightroom?

     

    Hal

     
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    Jan 22, 2012 8:43 AM   in reply to ngarefalosjr

    Good. I'm curious to know if using Lightroom to convert that NEF to DNG causes the problem to happen again.

     

    Hal

     
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    Jan 22, 2012 9:18 AM   in reply to ngarefalosjr

    I'd say so. It's good to keep backups of all your images.

     

    We're left with the question of how it happened, but I'm fresh out of ideas. Does your computer have a memory test application that you could run? If so, you might want to run it. Intermittent problems can be caused by hardware glitches.

     

    Hal

     
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    Jul 27, 2012 4:12 PM   in reply to ngarefalosjr

    I have seen this photo corruption issue cropping up regularly on forums (it also happened to me years ago). The worst thing is that it is a silent process: if one doesn't happen to look at a particular photo one may never know that it is corrupted.

     

    I put a feature request forward to implement an automatic photo integrity check into Lightroom:

    http://feedback.photoshop.com/photoshop_family/topics/photo_integrity_ check

    Please feel free to add your vote.

     
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    Jul 27, 2012 6:36 PM   in reply to quidquomodo

    There is such a feature, if you convert to DNG. The file includes a checksum of the image data, and LR and Camera Raw give a warning if the checksum no longer matches.

     

    Hal

     
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    Jul 27, 2012 6:59 PM   in reply to Hal P Anderson

    In the situation a year ago, was it media failure or something else that caused the “corruption”?

     
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    Jul 28, 2012 3:39 AM   in reply to ssprengel

    Good question. I suspect it was a hardware error of some sort, but the user never posted what he found, if anything.

     

    The backup NEF was fine, and re-converting it to DNG produced an OK image, so the problem was somewhere in the computer.

     

    Hal

     
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    Jul 28, 2012 5:21 AM   in reply to Hal P Anderson

    Hal, my understanding is that this check is done only when working on an image (DNG). So if the image is left alone - say for 6 months - Lightroom won't provide any warning, is that correct?

     

    1- So it looks like a very quick implementation of the data integrity check would be to do the check on demand for every DNG in the catalogue.

     

    2- At a second stage, this function could be extended by creating checksum for all types of raw files and also jpg.

     
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    Jul 28, 2012 5:49 AM   in reply to quidquomodo

    Yes, you're correct. It sounds perfectly feasible to keep a checksum in the database for other file types. I voted for your idea.

     

    Here's an interesting article: http://dpbestflow.org/data-validation/dng-validation

     

    Currently, the only way to check a large number of DNGs is to run the free DNG converter on them, which can take a long time and requires disk space for the second copies. The Adobe SDK has a function for checking the checksums, so it sounds like a relatively easy task to write a small app that would validate an entire directory tree containing DNGs. That could be quite fast and would be a good thing to run periodically.

     

    Hal

     
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    Jul 28, 2012 3:47 PM   in reply to Hal P Anderson

    Thanks for the link, this is a cumbersome workaround, but better than nothing.

     

    Maybe a plugin could be written that implements the SDK function to validate all the DNGs in a catalogue. But that still leave the issue for other raw files and jpg.

     
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