Olympus E-P1 RAW
Olympus E-P1 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 Olympus E-P1 high ISO RAW files compared to RAW files from the Canon T1i, Nikon D5000 and Panasonic GH1, converted with dcraw. We chose these models to compare, as they are the most compact models each respective company offers with movie capability.
As you can, the Four Thirds sensors of the Olympus E-P1 lag behind the APS-C sized sensors of the Nikon D5000 and Canon T1i in terms of noise at all ISOs above about 800, but not as much as we would have expected to see a year ago. Particularly at the higher ISOs, the Olympus E-P1 seems to do noticeably better in its RAW files than the Panasonic GH1 at high ISOs, the only other Four-Thirds model in the group. The E-P1 still lags behind the Canon T1i and D5000 (the latter of which has the cleanest files of any in this grouping), but not by as much as was the case for Four Thirds sensors only a short while ago.