Nikon D3100 High ISO RAW
Nikon D3100 High ISO RAW Image Quality
We've recently started looking at RAW files converted with dcraw, an excellent freeware raw converter. dcraw usually offers timely support for the latest cameras, but more importantly, it does not apply any noise-reduction, sharpening or other corrections such as geometric distortion correction to the output files. (We found that Adobe Camera Raw still applies some limited noise-reduction when its NR settings are set to zero, and it also applies other corrections depending on the make and model of the camera). There will always be differences between RAW converters, in terms of the sort of demosaicing algorithms they use (the processes by which they convert the separate Red, Green, and Blue data sets to an array of full-color RGB pixels), but dcraw seems to use a fairly generic algorithm that delivers good sharpness with relatively few artifacts, and can be counted on to not apply any noise reduction if you don't want it to.
Below are crops from Nikon D3100 high ISO RAW files compared to RAW files from the Nikon D3000, Canon T1i and Sony A290/A390. We chose these models to compare, as they are the entry level models from the top-3 players in the SLR space. (The Sony A290 uses the same sensor and processor as the A390, so results are directly comparable to both Sony models.)
Here, we can clearly see the Nikon D3100's dramatic improvement in noise levels over the D3000. We'd estimate at least an f-stop of improvement. The Nikon D3100 clearly outclasses the Sony A290 and A390 SLRs as well. The Nikon D3100 also outperforms the Canon T1i, but by a much smaller margin. We're not sure if the Nikon D3100 applies some NR in its RAW files; if it is, it's very subtle. The Sony A290/A390 definitely apply noise reduction to their RAW files, so these crops were taken from RAW files with NR set to the lowest setting available on each camera. (When working from RAW files, users typically will want all available information in a image, which is why perceptual noise reduction applied to RAW files is generally frowned upon.)