A method of calibrating gains and offsets for a two-dimensional detector array 10 comprising individual detector elements 14, including: (a) focusing a first incoming image signal at a first power level onto the detector array 10; (b) reading the corresponding electrical signals from the detector elements 14 as a first image frame at the first power level; (c) for each detector element 14, translating the first incoming image signal by a detector element distance onto an adjacent detector element; (d) reading the corresponding electrical signal from the detector elements 14 as a second image frame at the first power level; (e) focusing a second incoming image signal at a second power level onto the detector array 10; (f) reading the corresponding electrical signals from the detector elements 14 as a first image frame at the second power level; (g) for each detector element 14, translating the second incoming image signal by a detector element distance onto an adjacent detector element; (h) reading the corresponding electrical signals from the detector elements 14 as a second image frame at the second power level; (i) selecting a reference detector element 18; (j) determining the gain of detector elements adjacent to the reference detector element 18; and (k) determining the offset of the adjacent detector elements 14.