Different DSLRs offer different resolutions, ranging from 3 to 20Mpix. Higher-resolution sensors offer more detail, but their smaller pixel size often leads to higher noise levels, and consequently to lower dynamic range, tonal range, and color sensitivity. When printing under identical conditions, however, the performance differences can be either mitigated or accentuated by the choice of print size.
When one compares an 8Mpix image with a 32Mpix image printed on identical 20x30cm paper at 300dpi, the measurements for the original image do not give a good indication of the final result. The 8Mpix image will require no interpolation (2300 pixels for 20cm or roughly 8 inches), while the 32MPix image will have to be reduced significantly, with 4 original pixels averaged into a single pixel. This averaging operation will significantly reduce the noise in the 32Mpix, and accordingly improves the measurements provided for the original resolution.
Original measurements are useful to help gauge the actual image quality when viewed at 100%, but they do not predict how printed images will compare. In order to give a better prediction of how prints compare, a normalized version is more reliable and is provided based on 8Mpix.
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On the dxomark web site, we evaluate and rank many types of digital cameras with image sensors that vary widely in pixel count, pixel size, and digital signal processing. To ensure that sensor performance comparisons between cameras are fair, it is very important both to test under identical shooting conditions and to take viewing conditions into account.
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