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Speedy Petey

join:2008-01-19

Help with dead pixel, etc.

Click for full size
Canon EOS 7D
14mm 644s F10 ISO200

I am having a problem with dead pixels. I know I have several dead which I am VERY unhappy about, but this image shows MANY odd pixels; red, blue, purple, white, etc.

Can anyone tell me what this is and what my recourse is? Is this only something canon repair can deal with?

Thanks for any help you can give.


mromero
Premium
join:2000-12-07
The O.C.
kudos:1

canon repair can remap the pixels or turn them off.

Make sure you have a couple examples of long exposures with the lens cap on at ISO 100.

But you will have a few dead/stuck/bright pixels with any sensor to be honest.



nklb
Premium
join:2000-11-17
Ann Arbor, MI
kudos:2
reply to Speedy Petey

That is a VERY long exposure. That will show hot or cool pixels that you would never see with a normal exposure.

You will see this with ANY modern camera when dealing with exposures of this length.

You may help it a little bit by lowering the ISO, and there are other tricks such as image stacking a series of shorter duration shots to achieve the same thing with lower noise. (There's also dark frame subtraction which may be an option in your camera, but you may be annoyed with that causing any such exposure to double in length and still not give perfect results)

If you see those same hot or cold pixels with as ISO 100 shot that isn't over or under exposed, and isn't more than a second long, then I would be annoyed. As it is, there is no evidence of an issue.


Speedy Petey

join:2008-01-19
reply to Speedy Petey

Thank you nklb, that helps a lot.



DeathK
Premium
join:2002-06-16
Cincinnati, OH
reply to Speedy Petey

Although it's a little bit of work you can clone all those hot pixels out in editing software.
--
Photos By Greg Strong



rcroning
D700 Rocks
Premium
join:2005-05-21
Winnipeg, MB

1 edit
reply to Speedy Petey

You also may be aware that many stars have colours based on their temperature and whether they are moving towards or away from us.....red/blue shift. In this case however, the stars are moving, the hot pixels are not.

If you want to see how many hot pixels your camera sensor has, take a dark frame of the same duration.....dark frame = exposure with lens cap on.

You can then use certain software to subtract the dark frame from the other image and that gets rid of all the hot pixels. Remember, the dark frame must be of the same duration as the other image so the subtraction is complete. Star Trails is one such software and it's free.

Ralph.

P.S. Most cameras have dark frame subtraction built in...it's called long exposure NR. This however does not do as good a job as above.