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Dead pixels and hot pixels what is the cause

Discussion in 'Help Team' started by iamkhan, Jun 25, 2019.

  1. iamkhan

    iamkhan Member

    hi everyone.. what is the cause of this dead pixel when i am filming or taking pictures in low light with my canon 700d? what is the cause of this error? i've only had my camera for two years...
     
  2. Chester AP

    Chester AP Well-Known Member

    Do you mean 'pixels' (plural) or 'pixel' (one)? One you are unlikely to notice, but many may be noticeable.

    Somewhere in your camera body's menus there should be an option called 'pixel mapping' (or similar) which 'fixes' dead pixels.
    I don't know exactly what the fix does if the pixel in the sensor is permanently 'dead', but suspect it's a software fix to make the camera's software replace the dead pixel with the reading calculated from other pixels around it.

    If you have the user manual, try to find the relevant section and see what it tells you to do.

    Also, are you sure the problem is 'dead pixels'? Since you only notice it in low light shots or video, perhaps it is digital noise in underexposed parts of the image. When I once had a few dead pixels, they showed a black dots on light areas of the image, and the 'pixel mapping' process cured the problem.
     
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  3. PeteRob

    PeteRob Well-Known Member

    The manufacturing specification for sensors allows that there may be some dead and some hot pixels. Generally the most noticeable are hot pixels on a black or nearly black background. As the pixel position is fixed it is straightforward to remove them in post-processing. As said above, I think most cameras have a procedure for doing this. Otherwise it is straightforward to do in post.
     
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  4. GeoffR

    GeoffR Well-Known Member

    Assuming that you really do have a dead pixel, it is caused by a tiny impurity in the silicon wafer from which the sensor was made, hot pixels result from the same basic problem, how the impurity affects the sensor is dependent upon how it affects the circuit/s in which it features.

    As already said you are very unlikely to notice a single dead pixel but a small group of them will be visible. Pretty much every sensor will have one or two of them and the vast majority of people will never know. A single dead pixel on your sensor represents a 0.0000056% fault rate which is well within allowable tolerances for manufacture of sensors. That you have only had your camera for two years is irrelevant, if it is a dead pixel.

    One thing to note, a dead pixel won't move around the frame it will always be in exactly the same place and it will probably show as a black speck. If it moves around or appears as anything other than a dark speck (a bright spot for instance) isn't a dead pixel and is most likely noise of some sort.
     
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  5. iamkhan

    iamkhan Member

    Thank you for the replies.. how ever i have found fixes for this on youtube.. the steps seems rather simple to fix and attempt yourself, rather than taking it to a store.
     
  6. Chester AP

    Chester AP Well-Known Member

    What was the fix?
    Telling us might help us know what the original problem was.
     
  7. iamkhan

    iamkhan Member

    chester , i used this video tutorial

     
  8. PeteRob

    PeteRob Well-Known Member

    It must have been a hot pixel. The chance of seeing a dead pixel in a low light shot must be quite low.
     
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  9. iamkhan

    iamkhan Member

    It's most likely a hot pixel. As the pixel is red dot. I still haven't figured out why it happened, so i can deal with it in future projects. But there are ways to clean it up in post process editing. But rather have it not there before hand.
     
  10. Alhazred

    Alhazred New Member

    Dead pixels are pixels which do not receive any electric signal, thus they are black not being lit up.
    Stuck or Hot pixels are pixels where the electric signal is constant and doesn't change, depending on how the signal is received, the pixel takes its color. It can be of any color but bright for sure.
    Dead pixels are not repairable, they are coused by something phisically broken on the electric circuit that prevents the current to pass.
    Stuck/hot pixels have a chance to be repaired. When that happens to monitors you want to put on the area with the affected pixels a video which rapidly changes like white noise (what you see on analogic TV not tuned on any channel) or just the 3 RGB colors, that could "unstuck" the controller and make it command the pixel correctly again.
    On a camera sensor, I don't know what the "'pixel mapping" does, but for sure it can't fix a dead pixel unless it does by interpolation as Chester guessed.
     
  11. Chester AP

    Chester AP Well-Known Member

    The user manual for my Pentax K-5 is a bit vague about exactly what the process does, and comes with a warning not do do it if the battery level is low.

    'Pixel Mapping is a function for mapping out and correcting defective pixels in the CMOS sensor.'

    I have only run this once, when I had few dead pixels that showed as dark dots in a bright area of the frame and were clearly too small to be dust. The were only visible if viewing that part of the frame 'full size' on a PC monitor, and were not visible after running the process, hence my suggestion that their positions had been recorded so that they could be replaced when a RAW file is generated (and hence also corrected in the JPG file produced from the RAW one).
     

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