An investigation of Retinex algorithms for image enhancement

This letter introduces color constancy and Retinex theory for image enhancement. It classifies Retinex algorithms into four categories and provides their principles and implementations in general. The experimental results of Frankle-McCann, MSR (Multi-Scale Retinex) and PNSD (Projected Normalized Steepest Descent) Retinex algorithms are presented and compared. Moreover, variance and average gradient are proposed to evaluate the performance of the different algorithms.