dust on sensor, hot pixels or what? (E-P1)

dreilly

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I was processing some images from a restaurant shoot I did with an E-P1 and I found myself, "Gosh, that image looks like I shot it on film."

A little more staring at it and I realized why...there was dust on it! Little white spots to be exact, flurries if it were snow. It was actually on all the images, not just that one, though in most cases it was not noticeable at all.

I thought "hot pixels" were red. I thought the E-P1 had that dust-shake sensor dance thing going on. What am I seeing?

I shot some test shots and they were still there. Cleaned the Panny 20's rear lens...still there. Did pixel mapping...still there. Is this sensor dust?

(in the sample pic, you can see it especially in the dark area in the middle foreground). Like dandruff...

Doug
 

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shoturtle

 
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try the pixel mapping to see if it gets rid of it. If it is dust, clean the sensor it is pretty easy with the sensor clean kits.
 

dreilly

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I was probably at 1600. But would noise look so much like...dust? I'm used to chroma and luminance noise but this is very specific spots and the same spots from image to image, as well. I tried pixel mapping. Still there.

Anyone else positively ID this as dust on the sensor?

thanks so much for the comments (and the compliment on the photo). Restaurants are rich subjects, even when they're terribly lit with florescent light.
 

dhazeghi

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Testing for dust

The best way to test for dust is to shoot a uniform subject (blue sky works well), with a very small aperture (e.g. f/22) at low ISO (100) and the lens defocused (switch to manual focus, turn it to minimum focus distance). Dust will show up crisply as small dark ovals - usually a few dozen pixels in diameter.

I was probably at 1600. But would noise look so much like...dust? I'm used to chroma and luminance noise but this is very specific spots and the same spots from image to image, as well. I tried pixel mapping. Still there.

Anyone else positively ID this as dust on the sensor?

thanks so much for the comments (and the compliment on the photo). Restaurants are rich subjects, even when they're terribly lit with florescent light.
 

Phaedrus

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Noise it is, dust would appear as darker spots against a lighter background, that much is obvious.
 

dreilly

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Dhazeghi's dust test indicates some dust. I guess I should clean the sensor.

If it's noise, that's quite disturbing. I guess I could use the healing brush in LR to get rid of them, but one of the big bonuses of digital for me when I switched from film was no long hours doing dust and spot removal. Oh well!

Thanks everyone!
 

GaryAyala

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Looks like noise to me ... the spots are well defined (typically dust is OOF) and is most prevalent in the shadows/darker/underexposed areas.

Gary
 

GaryAyala

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Would noise be consistent in every image?
Sensor dust would be identical on every frame/file by location and size, I haven't any experience with the E-P1 at any ISO, but, if the noise/dust as exhibited in the example is noise then it would be present at every shot with similar ISO, metering and lighting conditions. Trying not to get too technical, but to answer the question, generally yes (unless the example was underexposed and the levels were boosted in post and all the other images were properly exposed ... then only the underexposed/boosted image would have noise ... or the underexposed image would have more noise than the images which were properly exposed). (Sigh ... hard to delivery a clear and concise answer due to all the variables ... even external heat, ala leaving the camera in the trunk of the car on a hot day will cause noise.)

I have a GF1 and I found that for my tastes, ISO's above 800 would have noise beyond what I would consider acceptable.

Dinner at ISO 800 w/ some noise reduction added in Aperture
Subscribe to see EXIF info for this image (if available)


Gary

PS- As a sidebar, I have found that a properly exposed higher ISO image would have less noise than an underexposed lower ISO image.
G
 

Streetshooter

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Gary, my point was that noise would not be consistent from image to image in the same pattern. Dust would be but noise, I don't think so.
You may have noise in every image but the pattern would not be consistent.
don
 

~tc~

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It depends on what you mean by consistent.

If you mean the exact same pixel, no - but can you really tell if the noise is in one pixel, or the one immediately adjacent?

If you took several pictures of the same/similar scene, the noise will likely be visible in the same dark areas and appear to be consistent,though.
 

BillN

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~tc~

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Is it fair to say dust will always be a dark spot, and therefore more likely to show up on a light background, where noise will usually show as a light spot on a dark background?
 

dreilly

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I went through my files on LR, zoomed in all the way. The USO (unidentified spotted objects) are in many but not all of the images. When they are present, however, they are always lighter and always in the same spot.
 

~tc~

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I went through my files on LR, zoomed in all the way. The USO (unidentified spotted objects) are in many but not all of the images. When they are present, however, they are always lighter and always in the same spot.
Are they in low-ISO (say, 100-400) shots too? Or, is there any correlation between ISO and number of spots?
 
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