Moments are certain integrals that capture the distribution of weight in a geometric figure.
The area can be thought of as a 0-moment if you assume that the gray is constant within the object. Then the area of an object is the 0-moment = simply the integral or the sum of values of the function equal to 1 inside the object. Saliency can also be understood as the 0-moment of the gray scale function, relative to the border of the object.
For the mathematics, see .
For the probability context see Moments of distributions.
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