In this system, the camera calculates an optimum exposure based on maximum and minimum brightness (contrast) measured across a a matrix of sensors perhaps 8, 10 or 12 across the area selected in the viewfinder. If the camera is set on an automatic exposure mode, TV, AV or Program, - it automatically sets the camera to give a "correct exposure based on this information. While the system takes account of all areas of the scene it places a greater emphasis on the sensors in the centre.
In the example on the right we see 10 segments- although the area of each is different, the tonal value of each is equal. This means there is a greater weighting placed on the area in the centre.
With some lenses like the D or G type Nikkor lenses, a 3-D matrix metering system also takes into account the aspect of the scene in focus.
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