Journal of Pattern Recognition Research

A simple power-logarithm histogram modification operator is proposed to enhance IR image contrast. The algorithm combines a logarithm operator that smoothes the input image histogram while retaining the relative ordering of the original bins, with a power operator that restores the smoothed histogram to an approximation of the original input histogram. Contrast enhancement is achieved by using the cumulative distribution function of the resulting histogram in a standard lookup table based histogram equalization procedure. The method is simple and independent of image content, and (unlike most existing contrast enhancement algorithms) does not suffer from the occurrence of artifacts, over-enhancement and unnatural effects in the processed images. The method can be applied both in a direct (DPL) and in an iterative (IPL) mode. Objective (computational) and subjective (visual) evaluation studies using a wide range of different IR input images showed that DPL and IPL both significantly enhance image contrast while retaining the overall image structure and preserving the perceptibility of small details and targets. DPL retains image structure slightly better than IPL, while IPL enhances contrast slightly more than DPL. Experimental results proved that the proposed method is a robust and efficient technique for effective IR image contrast enhancement.