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03-13-2017, 02:25 PM   #1
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Maze like pattern on photos

Hello,
After my last photoshoot when I got the photos on my computer I noticed that most off the photos seem hazy, overall lack of contrast and color. at first I assumed that I must have had a lamp facing at a unfortunate angle and that the problem was caused by the reflection in the lens but when zoomed in I noticed strange maze or canvas like pattern all over the photo (attached 200% crop of the worst example).
I checked the exposure settings and everything looks normal, ISO 100, shutter 1/13, f 8, and I shoot with original K-5 in DNG format
At one point I was hoping that this might be caused by the software (I use darktable) but not all photos of that day are affected, its like 60 % and there are correct photos in between those 'affected', I attached a 200% crop of the 'clean' one for reference, both photos were taken in a span of 2 minutes same camera same lens.
Have anyone seen something like this before ? Could it be a camera firmware issue or is my sensor failing ?
any insight in this issue will be appreciated.

Attached Images
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PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
03-13-2017, 02:33 PM   #2
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To me this looks like poor processing on darktable's part. Are you getting the same results when developing raws in-camera or using another desktop program?

Adam
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03-13-2017, 02:36 PM   #3
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Can you submit a photo with the exif data intact?
03-13-2017, 02:36 PM   #4
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I infrequently got this in the past, but with larger spacing, when resizing a batch of images. I have subsequently re-resized them with no issues.

Never used darktable.

03-13-2017, 02:52 PM   #5
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QuoteOriginally posted by SpecialK Quote
I infrequently got this in the past, but with larger spacing, when resizing a batch of images. I have subsequently re-resized them with no issues.

Never used darktable.
Just uploaded the same image processed with RawTherapee, for anybody interested here is a DNG file https://dl.dropboxusercontent.com/u/14290223/RAF_5321.DNG
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03-13-2017, 02:52 PM   #6
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What you're seeing is undoubtedly maze artefacts caused by Darktable... that said, it can happen to a greater or lesser extent in many RAW converters.

See the following:

Defects | DPanswers
03-13-2017, 02:58 PM   #7
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Darktable, RawTherapee and other Linux based Raw editors rely on dcraw as the raw converter, so its likely a problem with dcraw that will exist across multiple editors. Check to see if you can update dcraw for whatever platform you are running on and see if the problem still persists.
03-13-2017, 02:58 PM   #8
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The regularity of this pattern indeed suggests a software issue but I doubt it lays on the converter side since I tested more than one with the same result. I will reset camera firmware and monitor photos to see it this helped.
As for what Adam suggested, I don't have the camera with me now but I will post the result of that test.


Last edited by raff89; 03-13-2017 at 03:00 PM. Reason: spelling
03-13-2017, 03:25 PM   #9
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I just took your RAW and opened it in Photoshop (so ACR was the RAW converter). I upped the clarity and sharpening and exposure to bring out any artifacts, and it looked fine - see attached.

I think the fault lies (somehow) with DCRAW, not the RAW information or camera.
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03-13-2017, 03:30 PM   #10
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It's not your camera. Screenshot from zoomed in view of your raw file.
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03-13-2017, 03:52 PM   #11
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I can confirm that the issue is indeed on the software side somehow, I just checked in a Lightroom trial and the photo is fine.
This is a relief but I will try to find out why other software is misbehaving and if it can be resolved.
I have to add, I am using Darktable and RawTherapee on and off for the last 3 years and this is the first time I faced something like this, I switched to DNG just recently so maybe that has something to do with it ?
Regardless, thanks to all of you for your quick replies.
03-13-2017, 04:06 PM   #12
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Very interesting, I was reading about this the other day. In darktable, I can make the mazes go away by changing the demozaic method to VNG4 (with or without color smoothing). Your subject under this light must be some color that's hard to interpolate?
03-13-2017, 04:29 PM - 1 Like   #13
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I agree with others this is not a camera fault as all is well in ACR.

This is a demosaicing artefact. There are several choices available to you in RawTherapee, many are not particularly good with this image including Amaze and AHD (this is particularly bad). If RawTherapee is your editor of choice then consider selecting the vng4 demosaic algorithm - this does not display the artefacts you are seeing with whatever choice you made. Attached is a screen capture with Amaze and VNG4 demosaic - wait a couple of seconds for change





Last edited by TonyW; 10-20-2017 at 10:11 AM.
03-13-2017, 05:30 PM   #14
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For the record, darktable has not used dcraw as the base raw converter for about 3 years now. Instead, it uses Klaus Post's rawspeed. I have had this mazing artifact before. I find that it only happens at certain output resolutions. But changing raw format methods such as Amaze or vng4 can also help.
03-13-2017, 11:51 PM   #15
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I have never seen this problem. But I guess I should keep my eye open.

Can I request this to be moved to the Pentax Linux club later for referencing sake. This is good information here.
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