Dark image enhancement using adaptive piece-wise sigmoid gamma correction (APSGC) in presence of optical sources

Various classical enhancement methods may potentially enhance only the darker regions of an image in presence of illuminating sources. However, they distort and saturate the brighter regions consequently resulting in loss of original information and degradation of image quality. In addition, fringes and shading artefacts are produced around the optical sources as an outcome of image enhancement. Hence, it is desired to develop a more versatile enhancement algorithm which not only enhance the dark regions of an image but also preserves the information content of bright regions without much distortion. To overcome such problems, an adaptive piece-wise non-linear gamma correction technique is proposed here. The proposed algorithm employs piece-wise modified-sigmoidal functions which are derived from the image histogram so as to make it highly adaptive, nonlinear and versatile. The simulation results show that the proposed method gives better performance than most of the existing techniques in-terms-of objective and subjective measures.