An IR image gray-scale transformation algorithm based on human visual system

For human observation and advanced processing in actual applications, the gray-scale range expansion and scenery contrast improvement are the key problems of IR image processing. Aiming at the problems, by analyzing the IR image characters and human visual system, an IR image gray-scale transformation algorithm based on human visual system (HVSBGT) is proposed. The algorithm is combined threshold division and non-linear gray-scale transformation. The experiments of actual IR images from staring cooled and un-cooled medium wave IRFPA thermal imagers show that the proposed algorithm is effective on expanding the gray-scale range and improving the scenery contrast. Using the algorithm, the IR image entropy is increased and better than those using traditional algorithms. Meanwhile, by setting different thresholds, the sky background is inhibited and some object details are enhanced partially such as buildings, water surface and plants. For digital signal processor (DSP) hardware processing, a large number of exponential and logarithmic operations are simplified by using gray-scale mapping table. The HVSBGT algorithm can provide high quality IR images for subjective observation and lay a foundation for advanced algorithms. The realization of HVSBGT algorithm is of great value and practical significance for the thermal imaging systems and equipments.