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07-05-2009, 02:40 AM   #1
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Pentax K-m moire artifacts

Hello everyone.
I've noticed a strange glitch with my camera when shooting fabric with fine patterns.

Here are the examples:
1) Silk kimono
http://i.piccy.info/i3/4a/b2/4a6636dcda984f9770dabdf18307.jpeg

2) Jeans
http://i.piccy.info/i3/4e/58/17278b8174163c80f4080ebd2958.jpeg

Is there anything that could be done to prevent this bug?
Images processed with Adobe Lightroom 2.3 (Camera Raw 5.3)

07-05-2009, 03:15 AM   #2
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QuoteOriginally posted by onscreen Quote
Is there anything that could be done to prevent this bug?
A slight misfocus will avoid this.
This may not be what you need.

Try another RAW converter.
Try RAWTherapee, for example and try various demosaicing algorithms. They may not all show they same artefacts to the same extent.
07-05-2009, 04:54 AM   #3
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Thanks for help, Class A! I've tried Raw Therapee on those raws and VNG-4 algorithm seems to be the best. Still, artifacts remain but became less noticeable.
I wonder whether my camera is faulty or it's just a common problem among Pentax DSLRs that capture such materials as aforementioned fine-detailed cloth.

Last edited by onscreen; 07-05-2009 at 05:03 AM.
07-05-2009, 05:12 AM   #4
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QuoteOriginally posted by onscreen Quote
Thanks for help, Class A! I've tried Raw Therapee on those raws and VNG-4 algorithm seems to be the best. Still, artifacts remain but became less noticeable.
I wonder whether my camera is faulty or it's just a common problem among Pentax DSLRs that capture such materials as aforementioned fine-detailed cloth.
See here for the theory.

Bottomline, no dslr manufacturer dares to implement an antialiasing filter strong enough to prevent this.
You would need a 40Mpixel sensor and a strong antialiasing filter to get no moire for the same 10Mpixel resolution as the K-m has.

Would you have bought the K-m, if the effective resolution was 2.5 Mpixel, and garanteed no moire ?

George

07-05-2009, 05:43 AM   #5
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QuoteOriginally posted by onscreen Quote
Hello everyone.
I've noticed a strange glitch with my camera when shooting fabric with fine patterns.
I've noticed it a few times, here is one example I just uploaded. At this magnification (400%) you can notice the maze artefacts clearly.



I've been told the cause is the Bayer pattern used on most sensors (except Foveon) and the way the RAW picture is demosaiced. Different RAW processors can have different results depending on the algorithm used, my example was with Lightroom. Nice examples are here: Comparison of various RAW demosaicing methods

I also noticed that this happen more frequently with really sharp lenses (the Limited for example...).
07-05-2009, 08:34 AM   #6
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Well, it seems that it's not my camera's fault, what a relief!
Thanks all for your help
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