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?
The artifact shows up as a square in the middle of the photograph. The artifact seems to contains a mix colors, in lines. (It looks similar to what one might see on a graphic representation of a PC's defrag routine...hope that makes sense.) The artifact takes up less than 5% of the image. It is very strange.
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?
I exported the image to a JPEG onto my hard drive and found that the resulting file does indeed also contain the blemish. (Therefore, I'm assuming, as you state, that the DNG is corrupt). I always have converted my files while importing. Would the process be more reliable and free from corruption by converting after import?
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?
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.
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:
Please feel free to add your vote.
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, 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.
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.
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.