Author(s): M.Aarthy, P.Sumathy

The histogram equalization is an approach to enhance a given image.Histogram equalization methods are Histogram expansion, Local area histogram equalization (LAHE), Cumulative histogram equalization, Par sectioning, odd sectioning. Histogram expansion is a technique of histogram equalization. This research paper described three different techniques of expansion namely dynamic range expansion, linear contrast expansion and symmetric range expansion. Each of these has their specific strength and weakness. For coloured images linear contrast expansion is used. These all methods help in easy study of histograms and helps in image enhancement.