Effective Pixels and Foveon X3
SUMMARY: Sometimes advertised digital camera pixel counts can be deceiving.
Thanks to MalekTips reader kgelner for updating some of this information.
When comparing megapixel counts between digital cameras, be careful when comparing cameras containing the Foveon X3 three-layer sensor. You may think the resulting photos will come out larger in resolution than what the camera provides.
Most digital camera sensors can detect only red, blue, or green per pixel, using what is called the Bayer filter. A moire effect sometimes appears in photos as digital cameras try to accurately reproduce colors via dithering effects. To reduce the moire effects, digital cameras may use demosaicing effects that may result in "smearing" the photo, causing some loss of sharpness.
Foveon X3 digital cameras, however, have a sensor array, with three sensors for each pixel - one detecting red, one blue, and one green. The digital camera then merges the results together, supposedly resulting in sharper, warmer, and more pleasing photos.
Because of the extra detectors, a Foveon X3 digital camera that has, for example, 3.3 million detectors for red, green, and blue may advertise itself as being 10 megapixels (3.3 multiplied by 3 is approximately 10, though the resulting resolution of a photo will only be 3.3 megapixels). The actual quality of the photo, however, may differ depending on the digital camera's implementation, having approximately the same quality as a 5-8 megapixel photo taken with the Bayer filter.
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