Thermal imaging cameras detect infrared radiation to semi-quantitatively determine the thermal profile of the surroundings. Previously, no standard performance measurements have been established for thermal imaging cameras applications such as search and rescue and firefighting. The spatial contrast resolution in realistic atmospheric conditions was assessed through various full scale fires. Absorbing gas-phase combustion products greatly affected the ability of the TIC to measure local contrast in temperatures as a function of spatial frequency. A test was developed using a thermal gradient target to relate the voltage ramp output signal recorded in 8 bit digital tape format to the luminance projected by the LCD screen profile measured by a 16 bit CCD camera array with an IR filter. These relationship were nonlinear and unique to each imager tested. Measurements of the output signal only do not describe the final performance and a complete standard performance evaluation must measure the display luminance.