For users wanting additional drama in their photos, new app Noir Photo can add the dark, shadowy tones you're looking for. I tested the universal app on iPhone 4 and although I like this inclusion (you get more for your money), I found myself let down with the interface presented on iPhone (all of the screenshots you'll see are from the iPad version).
Noir Photo will first strip your image to black and white. Users can then select from several tinting options and relight the image using the Vignette tool, an orange circle that will appear directly on your image. By pulling and pinching the circle you can manipulate exactly where your new lighting will appear, highlighting what you want. There are also three exposures to play with that will adjust your levels of darkness. Six presets are available, which will set the Vignette in various starting positions. You can override the presets to your own liking by tapping and holding each icon. When you're finished, you can save your photo (which does seem to be high-res) using the button with the arrow in the lower right.
Once I figured out what each control did, I found Noir Photo easy to play with, but the measure of your success with the app will really lie in your original photo composition — bad photos won't necessarily be saved by sepia tint.
Noir Photo has some quirks I wasn't fond of. For one, the app's description boasts that the "preview area is huge and the controls are minimal." Maybe this is true on iPad, but it's not the case for iPhone users. On iPhone, your preview area is half your screen, with the controls taking up the rest. I'm not sure how iPad addresses landscape and portrait photos, but on iPhone nothing shifts. If you're working with a portrait, to see the image right side up you'll want to hold the device in landscape mode. If your image is horizontal, you'll end up holding the iPhone vertically. It's just strange.
Noir Photo doesn't run in the background, as the splash screen loads upon each launch, but it will retain the image you were last working on. In fact, the app will keep a photo open at all times — there's no option to clear your workspace. If you open a new image (which takes forever), that photo will take on whatever effects you gave to the last photo.
For its cost, I was expecting a smarter interface out of Noir Photo.