Strange pixelation/ghosting problem?

[joejubee]

Don't know what causes this- it chows up as a flicker in the view screen, and as you can see, it shows up in the image too. It happens once every 20 photos...???

joe@joefreelance.com

[Sebastian]

I'd say high-ISO banding. When at high sensitivities some cameras do this in shadow areas.

[SmartWombat]

Looks like under-exposure, at a high ISO setting.
Even on a EOS 20D I see that if I get the exposure seriously wrong.

[joejubee]

Thanks for the ideas, but the problem is- this is a point-and-shoot Canon Powershot A80, and I'm doing everything under the 'AUTO' feature. Is is seen on the viewscreen as a flicker, I'll try to get some perfectly-exposed images with this error so you can see that it might not be an exposure thing.

I was guessing it had something to do with a bad chip, or something mechanical/hardware issue...

thanks,

Joe

[another view]

If you're in an auto-everything mode, that might mean auto ISO too. Digital SLR's can shoot at a higher ISO before you'll start seeing noise like that - my Fuji S2 at ISO800 with a slightly underexposed image can look like that. But in a compact camera with a small sensor, you could get something like that at a much lower ISO. My Coolpix starts to show noise even at 200. Can you post the EXIF data?

[SmartWombat]

You usually get streaking like this wheen there isn't enough light through the lens.
It looks like amplifier noise on the sensor as it's reading out the image.
In a CCD sensor the read out is done by shifting the image one row at a time to the output, before the charge has time to decay.
Of course the sensor has to be in the dark (shutter closed) for this to work !

I don't know how far the Auto setting will turn up the ISO in dark conditions.
On my Minolta it only goes to 200 on Auto and you can manually set it to 400 - but it's noisy.