Hot and dead pixels
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
What have I got Dr?!:D
Neil
"Snow. Ice. Slow!" "Half-winter. Half-moon. Half-asleep!"
http://www.behance.net/brosepix
http://www.behance.net/brosepix
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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).
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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
http://www.behance.net/brosepix
Yes, quite likely, R.
Thanks for your interest.
Neil
http://www.behance.net/brosepix