grainy black w/ pentax optio S

[socram]

Hi, my wife and I bought a Optio S a few months ago and overall I'm pretty happy with it. The one complaint I have is that if there is a lot of black in the picture, it looks grainy (the black does that is). Most of the picture will look great unless it has a patch of black in it (or a really dark color) in which case the patch always has some amount of graininess to it (most noticable when you view it full screen - 1024x768 for me). Also, if it is a picture of people against a darker background, they kinda look like I cut and pasted them in the picture. Against a lighter background the picture looks great. These are pics taken at highest quality, highest resolution (2048 x 1536).

I don't know very much about photography in general, so my question is: is there a setting I need to fix in the camera itself (exposure, white balance, etc) or is this just a problem inherent to digital photography (or 3MP vs 5MP) or jpg compression?

Any help would be appreciated. Thanks!
Marcos

[Lee Yuan Sheng]

The graininess is probably due to digital to analog noise, and the camera is exhibiting fairly high noise levels in the dark regions which we call the shadow. This is a limitation of your camera, I'd think, but you can try applying some positive exposure compensation to see if it helps without overexposing the highlights (the bright parts in a photo). Some cameras tend to err on the side of underexposure.

On the second issue, I think the unnatural feeling could be due to a high contrast setting. Got a sample to show?

[Jason Dunn]

I think what you're seeing is digital noise - it happens when the digital sensor on your camera can't figure out what colour the dark background is. So it guesses, and what you see are those guesses. Dealing with noise is a big diffentiator in cameras on the market today - some are great at it, some are not. Smaller cameras tend to have less advanced sensors, so this isn't unusual.

There's a review of the Optio S here that mentions some of the cons, but it doesn't seem that this camera is any worse for low-light shooting than other cameras of its size:

http://www.dpreview.com/reviews/pentaxoptios/page14.asp

[David Prahl]

You can download free software that cleans up grainy/pixelated shots. That might be a good place to start.