2D histogram equalisation based on the human visual system

Histogram equalisation (HE) methods using the 2D histogram (2DH) have achieved a great success in contrast enhancement. The 2DH is constructed by using the occurrence of a local pixel pair (LPP) consisting of each pixel and its surrounding pixels. However, the 2DH-based methods often produce over-stretching artefacts because the low-textured regions primarily existing in the image induce a spike at some LPPs in the 2DH. To solve this problem, the 2DH is constructed by employing two properties of the human visual system (HVS) as follows: the HVS has the better brightness discrimination in the dark region according to Weber's law, and the HVS is less sensitive to visual artefacts in the higher-textured regions. To create a spike-free 2DH, a weighting function reflecting these two properties of the HVS is designed for the LPP. As compared with the popular 2DH-based methods, the HE with the proposed 2DH can effectively enhance the image contrast while achieving the best perceptual similarity score between the input and output images.