Canon T1i RAW
Canon T1i 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 Canon T1i high ISO RAW files compared to RAW files from the Nikon D5000, Olympus E-620 and Panasonic GH1, converted with dcraw.
As you can, the Four Thirds sensors of the Olympus E-620 and Panasonic GH1 lag behind the APS-C sized sensors of the Canon T1i and Nikon D5000 in terms of noise at all ISOs above about 800. The Nikon D5000 seems to have a slight edge over the Canon T1i, however keep in mind the T1i has 15.1-megapixels, while the D5000 has 12.3-megapixels, so it's no surprise that the D5000's larger pixels do a bit better when it comes to noise.
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