Pentax K-x High ISO RAW
Pentax K-x 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 Pentax K-x high ISO RAW files compared to RAW files from the Canon XSi, Nikon D5000 and Olympus E-620, converted with dcraw.
Of the four SLRs in this group, the Pentax K-x generates the cleanest RAW files (and probably the cleanest from any recent APS-C sensor model we've tested thus far), though it does look like the camera may be applying some noise reduction to its RAW files at higher ISOs even when NR is turned "Off". The Nikon D5000 comes in second, and the Canon XSi is a close third. Not surprisingly, the Olympus E-620 is the noisiest, as it also has the smallest sensor of the group. Excellent performance from the Pentax K-x here, though we wish it wasn't applying any NR to its RAW files.