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02-04-2017, 03:41 PM   #1
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White dots... Just once.

Hi, all

I recently received my K-1 and I'm quite impressed with it.

There is, nevertheless, an issue that's been troubling me: it shows-up in one of a series of shots (just a couple of days after receiving it) of a "capoeira" demonstration at the beach nearby where I live.

They all came out fine (except for the photographer's errors...), but on this one, when viewed at 100%, a strange splash of white dots appear in a section of the shot. I annexed the shot and a 100% crop of the section.

None of the other several shots taken at the same location, with the same settings, etc., show this - which is quite intriguing. Of course I have seen reports of the infamous "white dot" issue, but it does not seem to be an issue at ISO 200, which was the ISO at which this photo was taken.

Any ideas why this happened?

(PS. - I always shoot RAW. This apperas afeter processing, both in Lightroom and Capture One 10).

Your guesses are welcome!

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02-04-2017, 04:15 PM   #2
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Some burnt pixels perhaps?
02-04-2017, 04:35 PM   #3
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QuoteOriginally posted by LensBeginner Quote
Some burnt pixels perhaps?
Can be... But the following shots don't show them, although nothing was changed in between. That's what I find odd.
02-04-2017, 04:54 PM   #4
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I would suspect that sharpening has accentuated much smaller anomalies to the point of clipping. Naturally these guys were sweating. The sweat most likely was being cast from their bodies making small drops which are very reflective. Very small white specs then show in photo and became larger after sharpening. I see this being like the white spikes in photos of active water. Many PixelShift examples show this problem. I find that many PS samples to be over sharpened and the spray of water acts like the sweat.
Probably don't see this problem when shooting most shots but any liquid spray does not share the same spectral content as the objects being photographed.

I think that: Sharpening should be the last process before display and noises in the image will cause the least damage to the final image. Large sharpening on PixelShift raw data often explodes the parts of the image with movement.

Ronc

02-04-2017, 05:05 PM   #5
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QuoteOriginally posted by rechmbrs Quote
I would suspect that sharpening has accentuated much smaller anomalies to the point of clipping. Naturally these guys were sweating. The sweat most likely was being cast from their bodies making small drops which are very reflective. Very small white specs then show in photo and became larger after sharpening. I see this being like the white spikes in photos of active water. Many PixelShift examples show this problem. I find that many PS samples to be over sharpened and the spray of water acts like the sweat.
Probably don't see this problem when shooting most shots but any liquid spray does not share the same spectral content as the objects being photographed.

I think that: Sharpening should be the last process before display and noises in the image will cause the least damage to the final image. Large sharpening on PixelShift raw data often explodes the parts of the image with movement.

Ronc
Seems quite a reasonable explanation. It is true that this only shows up after processing. Though it may be not from sharpening, but, according to my own experiment with pp settings, due to pushing up shadows and adding a bit of clarity. So perhaps all combined. I first thoug of tiny bits of sand thrown up...

Thanks for the input.
02-04-2017, 05:18 PM   #6
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QuoteOriginally posted by Penta x Tuga Quote
Seems quite a reasonable explanation. It is true that this only shows up after processing. Though it may be not from sharpening, but, according to my own experiment with pp settings, due to pushing up shadows and adding a bit of clarity. So perhaps all combined. I first thoug of tiny bits of sand thrown up...

Thanks for the input.
Clarity is probably implemented via deriving an operator from the image but with limited spatial range.
There are few processes that work well if the spectral characteristics are not shared by all pixels.
I do less sharpening but increase the display level a tad. Haven't figured out units of a tad yet.

RONC
02-04-2017, 05:26 PM   #7
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As you can imagine, I was worried when I noticed this for the first time. But since I also noticed it had something to do with pp and didn't show up on any other pics, I'm not worried anymore. Just a tad curious about about the causes.
02-04-2017, 11:53 PM   #8
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Interesting answers, but nothing realistic.
How to test for sensor detect. Take a series of alternate white frames and dark frames with the same settings (manual mode).
If you don't find white dots, you can conclude that the dots you see on this picture were particles in the air at the moment you took that shot.
Can also be dust on the back element of the lens, as you changed the lens, the dust was gone.
Can also be dust on sensor, if you have the sensor cleaning turned on, you did not see dots in the subsequent shot because the dust was gone.

Usually when you see dots like those , in the image, it's either dust on the rear element of the lens, dust directly on the sensor, or hot pixels of the sensor, or other random fabrication induced defect of the sensor chip. Dust on the front element of the lens don't show up as dots in the image.

Regarding the hypothesis of post processing creating white dots in a dark area , I don't believe it.

02-05-2017, 12:16 PM   #9
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QuoteOriginally posted by biz-engineer Quote
Interesting answers, but nothing realistic.
How to test for sensor detect. Take a series of alternate white frames and dark frames with the same settings (manual mode).
If you don't find white dots, you can conclude that the dots you see on this picture were particles in the air at the moment you took that shot.
Can also be dust on the back element of the lens, as you changed the lens, the dust was gone.
Can also be dust on sensor, if you have the sensor cleaning turned on, you did not see dots in the subsequent shot because the dust was gone.

Usually when you see dots like those , in the image, it's either dust on the rear element of the lens, dust directly on the sensor, or hot pixels of the sensor, or other random fabrication induced defect of the sensor chip. Dust on the front element of the lens don't show up as dots in the image.

Regarding the hypothesis of post processing creating white dots in a dark area , I don't believe it.
The lens wasn't changed between shots and the camera was brand new (a couple fo days), so dust on sensor would be improbable. There are several images taken in quick succession and this is the only one where this occurred, so I'm inclined to go with the hypothesis of dust or drops of sweat in the air.

As for PP creating the dots: it's not a matter of "creating" them, but rather of enhancing something. Sure enough, if I load the image without any post processing, the dots are not visible. It's when I push the blacks up and add a bit of clarity (+15 in LR) that they show up.
02-05-2017, 01:43 PM - 1 Like   #10
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I've never seen sensor dust appear as white spots on the final image.
02-05-2017, 05:25 PM   #11
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QuoteOriginally posted by Penta x Tuga Quote
The lens wasn't changed between shots and the camera was brand new (a couple fo days), so dust on sensor would be improbable. There are several images taken in quick succession and this is the only one where this occurred, so I'm inclined to go with the hypothesis of dust or drops of sweat in the air.

As for PP creating the dots: it's not a matter of "creating" them, but rather of enhancing something. Sure enough, if I load the image without any post processing, the dots are not visible. It's when I push the blacks up and add a bit of clarity (+15 in LR) that they show up.
Do you mind showing us a small window of the image with no clarity adjustment and couple of adjusted ones? In looking on Wikipedia, clarity is sharpening in the mid range and at a few pixels from center. Meaning bringing up spatial frequencies back from Nyquist. If you do the demo, you might push to the limit on one.
I remember seeing Capoeira on the beaches in Brazil. Really interesting. That was years ago but daughter hosted Brazilian Dance Company just a couple of years ago. Watching the fine art of Capoeira was a treat.

Been an interesting problem.
RONC
02-05-2017, 06:13 PM   #12
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QuoteOriginally posted by Penta x Tuga Quote
I always shoot RAW. This apperas afeter processing, both in Lightroom and Capture One 10
Can you post a link to the raw file? Then I can inspect it using rt without demosaic.

Ingo
02-05-2017, 09:07 PM   #13
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QuoteOriginally posted by biz-engineer Quote
Interesting answers, but nothing realistic.
How to test for sensor detect. Take a series of alternate white frames and dark frames with the same settings (manual mode).
If you don't find white dots, you can conclude that the dots you see on this picture were particles in the air at the moment you took that shot.
Can also be dust on the back element of the lens, as you changed the lens, the dust was gone.
Can also be dust on sensor, if you have the sensor cleaning turned on, you did not see dots in the subsequent shot because the dust was gone.

Usually when you see dots like those , in the image, it's either dust on the rear element of the lens, dust directly on the sensor, or hot pixels of the sensor, or other random fabrication induced defect of the sensor chip. Dust on the front element of the lens don't show up as dots in the image.

Regarding the hypothesis of post processing creating white dots in a dark area , I don't believe it.
Post processing seems far more likely than dust that doesn't appear consistently between images.
02-05-2017, 11:52 PM   #14
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QuoteOriginally posted by lithedreamer Quote
Post processing seems far more likely than dust that doesn't appear consistently between images.
Fair enough. I'd be worried is my post processing was creating white dots in the middle of a black area. Also, it that was post processing that create white dots from the black by whatever constructive interference / digital rounding, it wouldn't create 3 dots, it would create thousand of white dots for the zone having the same level of black.
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