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12-02-2016, 08:39 PM   #1
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Banding in Pixel Shift Images taken with K-1

I am totally puzzled with this issue that seem to occur with latest upgrade of LightRoom CC and DCU5.


Has horizontal pale yellow bands clearly noticeable across the image. Attached are 2 sequential images, one with (PEN2163) and the other without (PEN2164) Pixel Shift.


I have not been able to find any reference anywhere to this phenomenon anywhere on the web.


Any clues??


Thanks.

---------- Post added 12-02-16 at 08:42 PM ----------

Please note that the images should be in the reverse order to that noted in the post. 2163 WITHOUT and 2164 WITH pixel shift.


Regards.

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12-02-2016, 08:45 PM   #2
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Was this illuminated by fluorescent lights? Faster shutter speeds might help.

More info here:
https://www.pentaxforums.com/forums/136-pentax-q/283932-rolling-shutter-problem.html

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12-02-2016, 09:22 PM   #3
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Yes it was Adam.


A small amount of natural (sun) light, but predominately tri-phosphor fluorescents.


What does rolling shutter refer to? I haven't heard that term before?

---------- Post added 12-02-16 at 09:25 PM ----------

Why did it occur with the pixel shift image but not the one without?
12-02-2016, 10:21 PM   #4
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QuoteOriginally posted by NeilS Quote
Why did it occur with the pixel shift image but not the one without?
I'm no expert, but I think the frequency of the light (on/off) coupled with the shutter speed may have caused different frames of the pixel shift image to have different lighting. Sort of like taking a movie of your TV. Different lighting on PS frames is what happened when I tried to take a long PS sunset photo. Different pattern, but the principle may be the same. Anyone else have any ideas?

12-02-2016, 11:38 PM   #5
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I wonder if this is an artifact of Motion Correction? Perhaps the change of lighting from pixel sample to pixel sample is identified as motion then perhaps correction kicks in. What happens if you develop the RAW with MC turned off?
12-03-2016, 02:14 AM - 1 Like   #6
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QuoteOriginally posted by NeilS Quote

[/COLOR]Why did it occur with the pixel shift image but not the one without?
Because Pixel shift uses electronic shutter, and normal mode does not.


-Tim
12-03-2016, 03:32 AM   #7
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Indeed, electronic shutter is the culprit here.
12-03-2016, 07:35 AM - 1 Like   #8
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As both NeilS's and rgknief60's experiences show, pixelshift is incredibly sensitive to differences in the light levels between the 4 exposures.

The light output of fluorescent bulbs, many LED bulbs, and even incandescent bulbs vary with the main's frequency (50 or 60 Hz) times some factor that depends on the lighting technology and circuitry. If the shutter time is not an exact integer number of cycles of the flickering light source, banding occurs.

In the case of NeilS, a longer shutter time would likely reduce (and may even eliminate) the effect. If you went from 1/60 sec, f/4.0 @ ISO 800 to 1/30 sec, f/4.0 @ ISO 400, the amplitude of the banding would likely drop by a factor of two. A setting of 1/4 sec, f/5.6 @ ISO 100 would probably reduce variations in the bands by a factor of 16. For tricky mathematical reasons, you might get lucky and discover that a particular shutter speed almost entirely eliminates the banding. So play around! Shoot a PS image of a blank canvas illuminated by your lights at each shutter speed and then look at the banding.

If you can't find a suitable shutter speed, then the you might also experiment with different CFL bulbs or LED bulbs from different makers.

12-03-2016, 09:55 AM   #9
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Candlelight is the most tricky with PS and same principle works there as well. 30 second PS exposures evens out most artifacts versus ~1sec candelight exposures.
12-03-2016, 03:30 PM   #10
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Thanks for all your suggestions. They are very helpful.


Now for experimentation......


Neil

---------- Post added 12-03-16 at 03:52 PM ----------

Just a further question to photoptimist.


Does that mean that if I used 1/50th sec exposure with 50Hzmains I should be OK??


Neil
12-03-2016, 06:18 PM   #11
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QuoteOriginally posted by NeilS Quote
Thanks for all your suggestions. They are very helpful.


Now for experimentation......


Neil

---------- Post added 12-03-16 at 03:52 PM ----------

Just a further question to photoptimist.


Does that mean that if I used 1/50th sec exposure with 50Hzmains I should be OK??


Neil
Almost certainly yes. I say "almost" based on two assumptions: 1) that the bulb is operating at exactly 50 Hz or 100 Hz (prevalent for circuits using simple rectifiers), or some exact harmonic multiple of 50 Hz; and 2) that the camera's 1/50 really is exactly 1/50 second and not some mathematical 1/3 stop value.

Good luck! And I look forward to hearing about your results!
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