An apparatus and method for reducing nonlinearity artifacts in an IR imaging system applies a non-linear correcting function to signals received from a microbolometer. The non-linear correcting function can be a second-order polynomial, a third-order polynomial, some other formula, or a table from which corrections can be interpolated. In embodiments, the correcting function is automatically adjusted according to an ambient temperature measurement, to which a non-linear correction can be applied, either in a separate step or as an adjustment to the correcting function applied to the microbolometer signals.