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fairy bombs
04-07-2010, 08:28
HI Folks

I recently played with my new 50D,doing long exposures of the night sky,I found one bit of bright red 'noise',always in the same spot,no matter the length of exposure.

I activated ICNR and that made it go away,also I imagine 'dark frame adjust' program will also work fine.

I heard the term 'Dead pixel' and also people talk about a 'Dead pixel removal program',is there such a thing as these two?

Should I be overly concerned with this one little spec of red??,I have ways of making not appear in photos,so thats good,But for a new camera I was a bit supprised,There is no other visable noise.

Thanks for any advice,FB

ricktas
04-07-2010, 08:51
The dead pixel removal programme is available is some cameras. It is often referred to as pixel mapping. See if your camera has it.

However your red pixel is a hot pixel, which is different to a dead one. Hot pixels are caused by the heat the sensor generates with longer exposures, which is why we have long exposure noise reduction, as that feature gets rid of the noise and the hot pixels in long exposures. the red pixel is nothing to be concerned about and you got rid of it the right way

A dead pixel, is just that, dead. It will never capture light again, in that instance pixel mapping gets rid of it by locating the dead pixel and then compensating for it, in every shot you take after performing mapping.

soulman
04-07-2010, 09:02
Same thing happens on my 5D11 under the same conditions, though Lightroom somehow automagically adjust the values. I've actually got a few on my sensor, maybe 4 or 5. A dead pixel is black. Ones that are stuck on a particular colour are called hot pixels. It's just manufacturing tolerances. Nothing to worry about.

fairy bombs
04-07-2010, 09:02
Thank you Rick for your kindly and informative answer-most helpful

cheers FB

jjphoto
04-07-2010, 09:48
Canon can remap the dead/stuck pixels but it costs $300 last time I checked a few months ago. I was told by another (leading) camera repair company that Canon does not sell this software to other repair companies so if you want it fixed then you have to give Canon more of your money. I don't know if there are third party programs that will remap the sensor. I shoot RAW which solves the problem entirely. Shooting jpegs is when you see dead/stuck pixels.

JJ

Astroman
04-07-2010, 10:21
You could try this method...
http://www.pearsonfaces.com/fpsurgeon/2007/04/better-dark-frame-subtraction-in.html