Sony DSLR-A550 High ISO RAW
Sony A550 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 Sony A550 high ISO RAW files compared to RAW files from other recent similarly priced SLRs. All were converted with dcraw with no noise reduction or sharpening.
Here, we can see that the Nikon D90 has the best performance in terms on high ISO noise, though it is also the lowest resolution SLR of the bunch (12.3-megapixels), so it has the advantage of larger photosites. The Canon T2i does quite well, edging out the A550 at higher ISOs despite being the highest resolution at 18-megapixels. The Pentax K-7 has a very similar number of pixels compared to the A550 (14.6-megapixels vs 14.2 respectively), and so not surprisingly, performance is quite similar, though the K-7 doesn't exhibit the bright red noise pixels the A550 shows at ISOs 3,200 and 6,400.