megapixel

Definition: Million pixels: measure of capacity of image capture device, usually digital camera based on number of pixels nominally available on CCD or similar sensor. * E.g. a 3 megapixel camera may offer some 3.34 million pixels on the sensor.
Mega complicated chain
It would be nice if the number of pixels on the capture device actually bore a direct relationship to the image resolution or some measure of the information that is actually captured; but life is not so easy on us. The fact is that colour information is captured in groups of four pixels: two for green, one each for red and blue (or, rarely, two yellows, one each for magenta and cyan) so each pixel's value must be extrapolated from the values of its neighbours. How exactly this is done are usually proprietory secrets of the chip manufacturers. Besides, the topography of the sensors themselves vary e.g. with Fuji's array rotated an eighth turn compared to others -- so you can never easily work out how the sensors arrive at the final image. Whatever method is used, rest assured it's not straightforward to get from number of pixels to image resolution.

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