Unlike its typical usage, the resolution of a digital camera doesn’t indicate its pixel count; it rather defines the ability of the camera to reproduce fine details.
This ability is influenced by various things and circumstances. It includes: the quality of the lens, ideal focusing, aperture, exposure time (blurry picture due to an unsteady hand) and a sensor with optical components in front of it (low pass filter, IR filter, etc.).
The weakest component in this chain is responsible for detail reproduction and is the part that downgrades the performance in the entire chain. During the first years of digital photography, the sensor with its limited number of pixels played this role. That changed with the development of increasing the number of pixels in the last few years. Today we frequently reach the physical limits such that the phenomenon of diffraction comes to play. But also the quality of the lens is important for detail reproduction, especially for the quality at the picture’s border.
The lens’ image quality is usually the best in the picture’s center but decreases towards the picture’s border. There the detail reproduction gets worse, as is shown in our sample. We observe that most 10 or 12 megapixel cameras can’t reproduce more details than the 6 megapixel Fuji F31 fd which we chose as our reference camera. Furthermore, they are significantly worse at the picture’s border.
The following image parts are from pictures from 4 different cameras. For every picture section the following camera applies:
upper left: Fuji F31 fd w/6.3 megapixels, upper right: Olympus 725 SW w/7.1 megapixels lower left: SLR- Kamera Nikon D200 w/10.2 megapixels, lower right: Canon 950 IS w/8.0 megapixels
Please note that the cameras where randomly chosen. According to our experience they show a typical behaviour for the represented camera class. To make the displayed images believable we decided to mention the cameras we used but we do not want to criticize a single model or manufacturer but the pixel race in general.
We’ve included the Nikon D200 with 10.2 megapixels for comparison to show that a SLR camera (single lens reflex camera) is on a different level than compact cameras. This is because they have higher quality lenses, bigger sensors, etc. Based on these comparisons, quality expectations are still satisfied with a higher number of pixels.
A look at "Flower basket, ISO 100" shows that Olympus and Canon can’t compete with the 6.3 megapixel camera when considering their detail reproduction. Examination of the basket structure from the 7.1 and 8 megapixel cameras shows that it isn’t recognizable anymore and single basket holes "melt" into each other, in contrast to the Fuji F31 fd.
The same is true in "Flower basket, ISO 400". In addition, the structures of the decoration threads frazzle or smear.
In "Motherboard, ISO 100" noise and blurring of details can be detected in the Olympus crop. A difference in the quality of detail reproduction isn’t really recognizable: the Fuji doesn’t show much noise whereas the Canon looks blurred.
The differences in the crops in "Motherboard, ISO 400" are more obvious. The 7.1 and 8 megapixel cameras lose quality and image errors increase. Though the 6.3 megapixel camera shows a little more noise as well, it reproduces more details than the cameras with more pixels.
The picture quality of the SLR camera Nikon D200 stays almost the same with both sensitivities.