Sparse readout method and apparatus for a pixel array

Information is obtained from the pixels of a spatial pixel array, such as a sub-atomic particle detector array, by discriminating between pixels that have and have not received actuating inputs, and obtaining outputs only from selected pixels. These pixels are determined by the pixels which have received actuating inputs, and may consist of the hit pixels and their immediate neighbors. The system monitors for the occurrence of an event of interest that occurs over time substantially less frequently than the rate at which actuating inputs are supplied to the pixel array, and obtains outputs from the selected pixels only for the times that correspond to the occurrence of an event of interest. The amount of data to be processed is thus substantially reduced.