Real-time implementation of modified Adaptive Histogram Equalization for high dynamic range Infrared images in FPGA

The performance of an Infrared imaging system is often measured by its Detection, Recognition and Identification (DRI) ranges. In thermal cameras, acquired images will be of high dynamic range (typically 15 bits) and lack adequate contrast. An Indium Antimonide (InSb) detector operating in 1-5 micron wavelength has responsivity of the order of 30mV/°K resulting in very low differential pixel values even after non-uniformity correction. Mapping the grey levels of high dynamic range thermal data (typically 15 bits) to invariably less dynamic range displays (typically 8 bits), without loss of information, is a challenging task. Hence, image enhancement technique that preserves all the information content and displays with proper contrast is inevitable. Conventional enhancement techniques like AGC, Histogram Equalization and their many variants have the tendency of generating excess noise and assigning more display dynamic range to the dominating temperature data while suppressing the non-dominating temperature data. In this paper, a new enhancement technique of modified Adaptive Histogram Equalization (AHE) is proposed with its real time implementation on FPGA for high dynamic range thermal data. Algorithm aims to retain information content of high dynamic range thermal data, with improved contrast, low noise while compressing the dynamic range to suit the display resolution.