1. A method for measuring size distribution of bulk matter consisted of randomly orientated granules, comprising the steps of: i) scanning an exposed surface of said granular bulk matter to generate three-dimensional profile image data defined with respect to a three-coordinate reference system; ii) segmenting said image data to only reveal regions of said image data having edges associated with distinct ones of said granules which are visible substantially without overlap; iii) estimating values of at least one size-related parameter for said revealed regions of segmented image data; iv) applying a geometric correction to each said estimated size-related parameter values to compensate for the random orientation of corresponding said distinct granules; and v) statistically estimating the size distribution of bulk matter from said corrected size-related parameter values.