Hot and dead pixels

NeilLNeilL Registered Users Posts: 4,201 Major grins
edited April 29, 2011 in Cameras
I'd also like to know how to read spots! Eg after exposures of 4sec in dark room and with black BG I see a half dozen spots of various colours red, blue, indeterminate. Sizes vary, looking at 100%, from larger than 1 pixel, seems to me, to less.

What have I got Dr?!:D

Neil
"Snow. Ice. Slow!" "Half-winter. Half-moon. Half-asleep!"

http://www.behance.net/brosepix

Comments

  • ziggy53ziggy53 Super Moderators Posts: 24,156 moderator
    edited April 28, 2011
    I moved this to its own thread so as not to hijack the original thread.

    Long exposures with a digital camera will normally produce "long exposure noise" because the sensor is not completely balanced output from each photo site to the next. Additionally, there are occasional imager flaws that produce stuck and dead pixels.

    These differ from high-ISO random noise in that they are not random, but predictable by each imager, ambient temperature and time.

    Most modern cameras have a "long exposure noise reduction" mode which produces a second dark frame exposure of the same duration as the original exposure. Any sensor anomalies, like the aforementioned long exposure noise, are subtracted using the dark frame digitally inverted and very effectively neutralized.

    Stuck and dead pixels need to be mapped out by the manufacturer (or sometimes by the user using an in-camera procedure).
    ziggy53
    Moderator of the Cameras and Accessories forums
  • NeilLNeilL Registered Users Posts: 4,201 Major grins
    edited April 28, 2011
    Yes, understand Ziggy, thanks!

    My interest was mainly to increase my knowledge, and in case I decide to take some remedial action in the future. And I also wondered if they indicate anything about the sensor's health, or about its "ageing"?

    All of the spots appear in the same place in all exposures at the same settings in that particular shooting series.

    They are quickly cleaned up so I'm not very motivated to do any more about them right now.

    Neil
    "Snow. Ice. Slow!" "Half-winter. Half-moon. Half-asleep!"

    http://www.behance.net/brosepix
  • RichardRichard Administrators, Vanilla Admin Posts: 19,967 moderator
    edited April 29, 2011
    It sounds like long-exposure noise reduction might take care of this for you. The downside is that the process takes as long as the exposure, so you will have to wait longer between shots.
    My Pics
  • NeilLNeilL Registered Users Posts: 4,201 Major grins
    edited April 29, 2011
    Richard wrote: »
    It sounds like long-exposure noise reduction might take care of this for you. The downside is that the process takes as long as the exposure, so you will have to wait longer between shots.

    Yes, quite likely, R.

    Thanks for your interest.

    Neil
    "Snow. Ice. Slow!" "Half-winter. Half-moon. Half-asleep!"

    http://www.behance.net/brosepix
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