Test for Hot pixels

jackdaw

How do I test for hot or dead pixels ??

take a black photo and then look for the pixels on my PC ?

thats what i think would be the best way ...

and what is the fix for it if i find some ?

I hear manual sensor cleaning ?

will that be just a quick blow down with the blower or a
proper wet clean ?

Shinjuku

If you haven't seen a dead pixel in your photos yet I wouldn't worry about it. I think I have two on my 40d and you really wouldn't notice them. they're easily removed in photoshop anyways. But there is no fix for hot pixels. There's a mythical "cheat" for fixing hot pixels on a 40d but I've never tried it.

jackdaw

weren-t they saying something about doing a manual sensor clean on DPREVIEW ?

anyway i just checked a black pic from my cam on the pc screen .. no bad pixels... and can-t seem to replicate the black dot issue either ...

challengemaster

Only way to fix 'em is to send the camera back for repair, which would prob mean a new sensor.

jackdaw

challengemaster wrote: »

Only way to fix 'em is to send the camera back for repair, which would prob mean a new sensor.

well it won/t need that ,,, but just for anyone else-s info there definetely was a simple fix ... a lot of dead pixels aren-t dead .. just asleep ..

its on dpreview somewhere... ill post the link later..

Shinjuku

jackdaw wrote: »

and can-t seem to replicate the black dot issue either ...

The black dot issue is only on the 5d MKII I think.

Ricky91t

Shinjuku wrote: »

The black dot issue is only on the 5d MKII I think.

Think he has one?
I stand corrected though

kensutz

Yes he has.

Burnt

To test for hot pixels take a long (with in reason say 15min) exposure with the lense cap on (Dark frame). Hot pixels will generally appear as purple-ly /white spots scattered across the image. And are literally a result of thermal noise across the sensor.

To remove this effect from any given image take a dark frame of equivalent length and subtract it from the subject image.

In addition to this there are flat field frames; variations in relative exposure, due to the inherent variation in the gain of the sensor across pixels. A mask can also be made to remove this variation, back take a picture of a uniformly illuminated surface of neutral colour (ideally gray), removing the dark frame of appropriate length and normalising the the frame. Then divide this through the subject image to achieve uniform exposure across the image i.e. a flat field.

Hot pixels and field variation are a fact of life on sensors and can't be eliminated; stuck or dead pixels are however unacceptable on a fresh sensor, you should consult your supplier for your warranty entitlements

jackdaw

Burnt wrote: »

To test for hot pixels take a long (with in reason say 15min) exposure with the lense cap on (Dark frame). Hot pixels will generally appear as purple-ly /white spots scattered across the image. And are literally a result of thermal noise across the sensor.

To remove this effect from any given image take a dark frame of equivalent length and subtract it from the subject image.

In addition to this there are flat field frames; variations in relative exposure, due to the inherent variation in the gain of the sensor across pixels. A mask can also be made to remove this variation, back take a picture of a uniformly illuminated surface of neutral colour (ideally gray), removing the dark frame of appropriate length and normalising the the frame. Then divide this through the subject image to achieve uniform exposure across the image i.e. a flat field.

Hot pixels and field variation are a fact of life on sensors and can't be eliminated; stuck or dead pixels are however unacceptable on a fresh sensor, you should consult your supplier for your warranty entitlements

OK so stuck or dead pixels , how can i test them .. im only paranoid with my new camera here ....

I took a few black pics and seems i have no spots ... so that indicates i have no stuck or dead pix....?

AnimalRights

jesus woman.

Burnt

A stuck pixel is one that is on all the time; as opposed to a hot pixel, it isn't proportional to exposure length (thermal noise). So it would appear as a white pixel on a short exposure (sic) dark frame. When testing for stuck pixels make sure to shoot several frame (~5) and only count the ones that repeat the across all image as stuck pixels, as bursts of Gamma radiation (cosmic rays) can cause saturated pixels on extremely shot exposures.

A dead pixel will appear as a black spot on a long exposure flat field.

Stuck pixels are very rare, dead ones are more common but i would feel that the quality control process of major sensor manufacturers would find them. So don't worry to much

PS your test would indicate that you have no stuck pixels

jackdaw

from dpreview...

Try the mythical manual sensor clean method that used to work with the old 5D and just worked with someone else 5DMII on another thread. Put the lens cap on, put it in manual sensor clean mode (which lifts the mirror) and wait a few minutes. You don't have to physically clean the sensor, just wait, then turn off the camera and then on again. Try a test shot. Sometimes it works, sometimes it doesn't.

Borderfox

Take off lens cap
open door
Go out and shoot
Dont worry about it!!

kensutz

You're probably better off just shooting instead of getting paranoid about some problems which might or might not appear in your camera. If I did that with everything I bought a) I wouldn't enjoy it and b) I'd be extremely wary of every single thing I bought.

challengemaster

kensutz wrote: »

If I did that with everything I bought

You'd be testing for a few years! :pac:

delly

Dead pixels are something which some people make a big deal out of, yet actually cause little or no real ill effects. As others have mentioned you really should just go and take some pics as 2 or 3 bad pixels of 10 million will not be noticed.

kensutz

challengemaster wrote: »

You'd be testing for a few years! :pac:

Shush