Retrospective shading correction algorithm based on signal envelope estimation

An additive retrospective non-parametric algorithm for the correction of the inhomogeneous intensity background of images, commonly known as shading, is presented. The algorithm assumed that an original unbiased image was corrupted by slowly-varying shading that could be estimated from the signal envelope in a process analogous to amplitude modulation detection. Unlike other filtering algorithms, the algorithm did not require pre-processing, parameter setting, user interaction, computationally intensive optimisation algorithms nor a restriction in size of the objects of interest relative to the scale of background variations. The algorithm provided satisfactory results for artificial and microscopical images.