A thermography process for thermal imaging systems produced in quantity, including an imaging sensor and an ambient temperature sensor, that includes operations at three different places in the manufacture and actual use of the system. A temperature calibration may be performed on all units of a given design at a small number of controlled scene temperatures at one ambient temperature to produce a function that relates sensor signal to scene temperature. The function is determined for each individual unit and may be unique for each unit. Selected calibrated units may be subjected to a qualification test where they are exposed to larger number of controlled scene temperatures at a plurality of controlled ambient temperatures and the errors between the calibration derived function and the observed results and/or the actual scene temperatures at the various scene/ambient temperature combinations may be derived and put into a table that is loaded into all production units. In actual use of the imaging system, for any given actual observed signal and temperature sensor values, the corresponding scene temperature and/or error may be derived from the table and used to modify the temperature value from the calibration function.