Abstract: In a gamma camera system a computer calculates the x and y coordinates of scintillations and a pulse height analyzer determines if they are within the proper amplitude limits for being displayed on a cathode ray tube at corresponding coordinates. Means are provided for correcting nonuniformity or lack of correspondence between the positions of the scintillations and their calculated coordinates. In an accumulation mode, a first memory matrix stores pulse counts for incremental areas of the radiation field when a uniform source is presented to the detectors. When a predetermined maximum number of counts is reached in at least one memory location accumulation is interrupted at which time other locations have fewer counts in them. In the run mode counts are stored in corresponding locations in a second memory matrix and these counts are compared continuously with those in locations in the first memory.