Whatever is causing the posterization, it certainly isn't the camera or RAW converter. I'm not seeing any posterization on my calibrated monitor anywhere in the image. What are you using to calibrate your monitor?

If the posterization doesn't show in prints, that should be a big clue that it's the display system at fault. Definitely check into a new monitor, and be aware that any LCD will exhibit a certain amount of posterization unless you get one of the 10-bit Eizo ColorEdge monitors that costs an arm and a leg and a gonad or two. I have a Samsung 213 LCD that does this slightly with certain saturated colors, but it's not visible with most images. CRTs are less susceptible to banding and posterization, but are generally fuzzier and have less brightness and contrast than LCDs.

the image is fine.
it's most likely your screen.

I have the same problem with my 20D.
my screen is calibrated so the colors are good but it's a CRT attached to a laptop. yukky posterisation but I know it looks fine when I leave away the laptop-step.

BTW I looked at the image on my non-calibrated 17" MultiSync LCD 1760NX at work, so I would not worry too much about getting a 10bit depth LCD.

I recently purchased a 1ds MkII and have been shooting RAW and processing the files in Photoshop CS. I've noticed that the transitions between the tones in the shadows aren't that smooth - I'm getting some posterisation. Just wondered if anyone else is experiencing the same thing? Things improve if I overexpose slightly (expose to the right) to avoid clipping and to allocate a few more bits to the shadows but this leaves the black level in the image looking a bit flat and washed out - as soon as I try to take the blacks darker again to give the image some contrast the posterisation returns. Am I expecting too much from this camera or could I have a faulty one?

Example image:
http://www.andyforrest.co.uk/image.html

The posterisation is apparant on the right hand side of the image in the fold of the fabric.

Any help / views greatly appreciated.

Hi Jonathan,

Yeah, it might be my monitor. I've printed some images off and I can't see the posterization on my prints. I'm using Gretag Macbeth Eye One to calibrate my monitor - its a Sony CPD-G400, that's about 3 years old - maybe its the age of the monitor?

I wondered if it might be the camera as I'd read on another forum about the effect of less bit depth in the shadow area due to the way digital sensors record light on a linear rather than logrithmic scale but my fears may have been unfounded. Thanks.

I use dual Apple 20" Cinema displays which I calibrate with Monaco Optix, and see no posterisation either.  I brought your image up on a third Apple Cinema display which isn't calibrated, and I see the posterisation.  Looks like it is indeed the monitor.

I see no posterisation either. I take it you have the basics of bit depth on your display sorted i.e. 'true colour, 32bit' etc..? The monitor might not be at fault and it could be the graphics card.