Signal-processing algorithms for display and enhancement of IR images

A survey is presented of algorithms for the display and enhancement of infrared images developed over the last several years by the author and his colleagues. Our algorithms were driven by the need to map the raw recorded signal (digitized to 12 bits for single frames grabbed with our cameras) into 8-bit values for soft-copy display or real-time automatic- contrast operation on live camera imagery. We group the algorithms into two broad classes: global monotonic mappings in which the radiometric trend from low to high in the recorded image is retained in the displayed images; and mappings which depart from the global/monotonic constraint for purposes of local contrast enhancement. In the discussion of global display algorithms, we compare the Histogram Projection algorithm devised several years ago and widely used in auto-contrast circuits with the standard technique of Histogram Equalization. For complex histograms and wide dynamic range scenes, a compromise or `hybrid' of the display allocation specified by these two histogram techniques is desirable.