This study proposes an improved data reduction method for the applications of transient liquid crystal thermography on film cooling effectiveness measurements. On the evaluations of film cooling effectiveness and heat transfer coefficient, an "equivalent step temperature"(EST) is proposed to replace the Duhamel's superposition principle which is conventionally used to account for the actual temperature rises in both free-stream and injection flows rather than the ideal step temperature changes. For obtaining both values at over thousands of measured locations, the current data reduction method can effectively reduce the calculation time as compared with the conventional Duhamel's superposition method, but adds only negligible errors. (C) 2001 Elsevier Science Ltd. All rights reserved.