where the latter is the central moment and p is the moment order. Normalized moments invariant to translation, rotation, and scaling [1,9] are obtained with
This orientation and the one orthogonal to it are the principal axes of the object. The eccentricity of an object is given by m mp
and that ranges from 0 for a perfect circle to 1 for a straight line.
Spatial moments have been used to quantify breast tumors [2,4], mammographic calcifications , and blood cells . The effectiveness of spatial moments has been shown to deteriorate when the object is less than about fifteen pixels wide or when parts of the objects are relatively small . A modified set of invariant spatial moments normalized with respect to standard deviation  has been reported to improve classification and sensitivity to noise.
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