Dead Pixel, Hot Pixel, or Just a JPEG Anomaly????

[ruettgers]

Please help. I need your expert opinions.

I recently bought a digital rebel and a 20D. The 20D seems to get these few pixels that are almost white. It happens every so often and is never in the same place. I am sure that it is not dust inside the SLR area, but I am afraid that it is something worse.

I am wondering if it is a a dead pixel, hot pixel, or just a JPEG mess-up, but it happens only on the 20D.

Thanks for advice in advance.

[lancea]

Have you tried saving as RAW with JPEG? That might give a different perspective on what's happening. Probably a silly question, but presumably the "almost white" pixels are not occuring in the brighest part of the image (histogram will show if you're over exposing)?

Any chance of posting a sample?

[ruettgers]

I have been using JPEG, but now I am testing RAW. Why would RAW help?

No... The hot pixels are small and can be in dark areas as well as lighter areas. I am not talking about the bright spot on a bald man's head at 12 noon ;-)

Thanks!!

[lancea]

The JPEG files are processed in the camera. The RAW files are - well - raw. They aren't compressed, sharpened or colour-adjusted.

[ruettgers]

Oh... I meant, does RAW have hot pixels, or is that just from JPEG. I've also been reading up on the Net about CCD... the sensor on digital cameras may be the reason, but it is still unclear why I am getting these annoying specs.

[lancea]

No. Neither format should have hot pixels. It's a good principle of fault finding though that you should track the problem to the lowest level. Unless you've got Canon's test equipment, the RAW file is the lowest level you can go to. If it were hot pixels, I wouln't have expected them to move around.

What you have doesn't sound good, and probably needs a trip to the service centre. It's remotely possible your firmware is corrupt, so you could try refreshing that with the latest version.

[MTalley]

On an off-chance here - do these primarily appear when you are using the flash?

[etaf]

these may help you

http://www.starzen.com/imaging/deadpixeltest.htm
http://webpages.charter.net/bbiggers/DCExperiments/html/body_hot_pixel_facts.html
http://www.imaging-resource.com/ARTS/HOT/HOT.HTM

[Pekka]

If there are hot pixels in your files Canon service can set the camera to map them out (at least for 1D series). They do a black image with 1s ISO 1600 exposure and see where the bad pixels are. Then they use the service software to tell the camera that info. The pixels are fixed on sensor level (using data from all 8 surrounding sensor elements) and the camera handles it in realtime. Few mapped pixels are not a problem. There can be thousands of mapped pixels before you start to see them as anomaly in final image.

[lancea]

Interesting posts and links - but ruetguerrs says his are never in the same place. Is that common too? Etaf's links talk about pixels becoming "hot" in certain circumstances, so I guess that could explain why they appear to move.

[PhotosGuy]

I'd like to know the answer to the question, "do these primarily appear when you are using the flash?", too.

[ruettgers]

On an off-chance here - do these primarily appear when you are using the flash?
No... I get hot pixels with or without flash.