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05-28-2008, 04:57 PM   #1
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white dots

Hi all,
I am a new digital camera user. I shoot a lot of long exposures under poor lighting conditions and I have noticed, when zooming into an image on my computer, that there are white dots all over it. Is this what is referred to as "noise"? Does anyone have any advice or insight into what to do about this?
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05-28-2008, 05:16 PM   #2
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To me it looks like dust or dirt on your sensor.
05-28-2008, 05:17 PM   #3
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Yes, that's one type of noise. More specifically, hot pixels caused by the sensor overheating. What camera do you have? For long exposures (>1 sec), the K20D forces a dark frame subtraction, where it takes the same shot with the same settings, but without opening the shutter, that way it can map out the wonkiness and subtract it from the image. The K10D does this too, but you can disable it in the menu. Not sure about the DFS specifics of the other models.

Joe
05-28-2008, 05:19 PM   #4
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QuoteOriginally posted by Oldschool Quote
To me it looks like dust or dirt on your sensor.
Yeah, maybe so.

05-28-2008, 06:02 PM   #5
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I do have the K10. How do I go about doing the "dark frame subtraction"? I have done a sensor cleaning by doing it through the camera functions. I don't have any white dots when I do a shorter exposure. It only seems to happen when I do exposures of say around a minute.
05-28-2008, 06:59 PM   #6
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It's called "Noise Reduction" on page 3 of 6 in the custom function menu. It's turned on by default. You'll know it's working, because after you take a picture, the camera will automatically take another.

The Sensor Cleaning function just locks the mirror up so you can access the sensor to clean it. Are you cleaning it while you do that?
05-28-2008, 07:16 PM   #7
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Dust on the sensor is black, not white.
That is noise
05-28-2008, 07:56 PM   #8
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Looks like hot pixels from the images I've seen about the K20D. Wouldn't noise be more even across the frame & not just random specs like that?

05-28-2008, 09:27 PM   #9
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I'd call it hot pixels. If you shoot raw, most raw processor automagically map them out when processing the picture. All cameras have some. Currently, there's a particular setting on the K20D that seems to generate hot pixels (though I didn't really see it on mine). Supposedly, Pentax is releasing a firmware fix. They also have a feature to map out hot pixels in the camera (Canon also has this, I believe).
05-28-2008, 09:38 PM   #10
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If you turn your noise reduction to "strong" those should dissapear entirely.
05-29-2008, 05:55 AM   #11
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white dots

Thanks for your help. I will change my noise reduction to strong and if this doesn't work I will keep a look out for the firmware to get rid of this. I "know" it's not dust because it only shows up during long exposures. It is a real disapointment to zoom into an image and see those spots and know I have to spend time getting rid of them in photoshop sinse I can't usually reshoot.
Thanks again,
Angela
05-29-2008, 06:47 AM   #12
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There won't be an update for the K10D, only for the K20D. It seems like Pentax stopped working on firmware update for the K10D when the K20D came out. If you shoot in RAW mode, your software should get rid of these if they are hot pixels (and they seem to be). If you shoot JPEG, well I think your stuck with them (maybe someone else know something I don't about JPEG and hot pixels).
05-29-2008, 08:13 AM   #13
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QuoteOriginally posted by angela Quote
Thanks for your help. I will change my noise reduction to strong and if this doesn't work I will keep a look out for the firmware to get rid of this. I "know" it's not dust because it only shows up during long exposures. It is a real disapointment to zoom into an image and see those spots and know I have to spend time getting rid of them in photoshop sinse I can't usually reshoot.
Thanks again,
Angela
If you're using Photoshop, then just shoot raw and they're automagically removed, along with your disappointment. This has been a feature of Photoshop and a lot of other raw processors for a long time.
05-30-2008, 07:12 AM   #14
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White dots

I am shooting in Raw but photoshop doesn't automatically take away the dots. What I attached to the first post is a raw file (turned TIFF) in photoshop. Is there something I have to ask photoshop to do. I checked my camera and the noise reduction wasn't actually on (stupidly) so I hope this makes all the difference.
05-30-2008, 09:11 AM   #15
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Yeah, turning the NR on will probably do it. One thing to consider, though, if you're shooting repeatedly with the same settings, you may want to manually take one dark frame (with the lens cap on or whatever) and subtract it all later. With NR on, all long exposures take twice as long. My last camera forced NR over a second, and I missed a lot of good fireworks during the dark frame.
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