Pentax K-7 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 de-mosaicing 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. (That said, looking at the ISO 6,400 and above examples below, it's clear that dcraw's de-mosaicing approach does have some tendency to produce rectilinear artifacts in response to high noise levels.)
Below are crops from Pentax K-7 RAW files compared to RAW files from other prosumer SLRs, converted with dcraw.
The crops above compare the Pentax K-7 RAW noise performance to that of its sibling, the K20D, as well as to other popular prosumer models, the Canon EOS 50D and Nikon D300. All cameras were equipped with our Sigma 70mm f/2.8 EX DG Macro reference lenses, stopped down to f/8 for maximum sharpness. (We've replaced our Pentax mount version with one that doesn't have the softness our previous copy had in the right-hand side. That's why the scale crop from the K20D is a bit soft compared to the others, as it used the older lens.)
Out of the four, the 14.6-megapixel Pentax K20D has a slight edge over the others in terms on noise. The Canon EOS 50D appears to be the noisiest, but that's no surprise, since it has the smallest photosites of the group (15.1 megapixels and a slightly smaller sensor). The 14.6-megapixel Pentax K-7 appears to be only slightly noisier than the Nikon D300, which is actually very good performance, considering the 12.3-megapixel Nikon D300 has larger photosites.
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Note: For details, test results, and analysis of the many tests done with this camera, please click on the tabs at the beginning of the review or below.