Apparatus for determining parameters of any number of selected regularly or randomly oriented particles, or images or image patterns thereof, of various size and shape lying within a discrete region. A scanning device is swept over the discrete region causing the generation of electrical signals in response to the interception of the boundaries of one or more of the particles. Apparatus, including, for example, a light pen, for use in cooperation with a display of the feature images is operated to best identify, select or prepare for analysis features of interest within the discrete region. In cooperation with such apparatus appropriate logic and electronic circuitry which is adapted to receive the initially generated signals provide, in response thereto, other signals related to the feature or features of interest and any particular parameter related to those features.