Issues with hot pixels, do you think my camera has a problem?

Discussion in 'Beyond the Basics' started by jon_k, Jul 14, 2007.

  1. jon_k

    jon_k TPF Noob!

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    A while back I was playing with the camera and tried the pixel mapping option wondering what effect it would do when I was new to my camera. A while later I read an article about hot pixels and how to test for them, what they are, etc. This is when I became self conscious about hot pixels. I've since run pixel mapping a few times, but it doesn't seem to help. The big problem is obviously on high ISO, but today I found a problem in a low iso situation!

    Below is a crop at 100% size of a picture I took today. The only processing was a crop.
    # Exposure = 40.00000 second
    # F/stop = F22.00
    # ISO = 100

    Is this a problem? Or would your camera act the same way in this condition? Did my running pixel mapping totally screw my cameras calibration? Is there something special about properly doing a pixel mapping? The camera is only 2 months old, is it abnormal to have so many hot pixels at the settings above?
    [​IMG]
    Full size image available here.http://uberleet.org/~jon/noise-lg.jpg

    After resizing and post processing the damage can't be noticed.
    [​IMG]
     
  2. DRodgers

    DRodgers TPF Noob!

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    I've never used mapping but just about any camera will have hot pixels especially at low iso long exposure images .The camera uses a built in data base to measure the info with previous images and sometimes gets lost when it cant read all the info needed in low light ..

    Thats How I understand it .. please someone pipe in if they have a better explanation.
     
  3. jon_k

    jon_k TPF Noob!

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    Well I'm back with new news on the subject.

    I was post processing the jpeg images, as all my examples above are from.

    My camera was set to take JPEG+RAW, and I've cracked open the RAW files.

    The RAW files of the exact same exposure don't have this noise. This suggests it has nothing to do with my CCD.

    Does anyone have any guess as to why the RAW files are clear of any of these specks? I would be very interested to know, if anyone has any idea.

    [​IMG]
     
  4. Garbz

    Garbz No longer a newbie, moving up!

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    Actually this has everything to do with the CCD. Odds are that the software you use to process the RAW file has a significantly better noise reduction algorithm than your camera and thus it automagically removed them when you loaded the RAW file. What you are showing is a common to every camera and not a fault.

    Hot pixels become evident when you strain your CCD, and a 40 second exposure is straining it. You may also find you have hot pixels if you take just a 5 second exposure at ISO800 aside from the extra noise.

    Most cameras have a long exposure noise reduction feature which basically takes a second frame without opening the shutter with exactly the same exposure times. The stuck pixels are consistent over various exposure times and this second frame serves only to show which ones are hot for that given exposure and remove them.
     
  5. WingedPower

    WingedPower TPF Noob!

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    [​IMG]

    Long Exposure = more noise and amplified hot/dead pixel effects.
    Heat = amplified effect as well.

    The camera and the software probably use two different algorithms to process the sensor data. The process to blend color/luminance info from neighboring pixels is expensive, without dedicated hardware, so the software application probably does this, but the in-camera probably doesn't.

    There is also the issue of hot pixel mapping. It could be that it only triggers when you use the raw conversion software? Dunno, it's been a while since I used an Olympus.

    I do know that JPEG will amplify the hot pixel/dead pixel/noise effect because of the visual 3x3 or 4x4 blocking that is employed. I've had images come out noise-free when taken with RAW, but the in-camera JPEGs come out noisey.

    You can probably confirm this by using a third party RAW conversion application, to see if something isn't being done during the Olmypus Camedia software conversion process.
     
  6. jstuedle

    jstuedle No longer a newbie, moving up!

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    What you are seeing is typical of long exposures and digital CCD's. I am really surprised that it's that apparent at ISO 100 and 40 sec. It's usaly seen at higher ISO settings.
     

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