  This report describes the experimental results obtained using a proposed
variational Retinex algorithm for controlled illumination correction. Two
colour restoration and enhancement schemes of the algorithm are presented for
drastically improved results. The algorithm modifies the reflectance image
using global and local contrast enhancement approaches and gradually removes
the residual illumination to yield highly pleasing results. The proposed
algorithms are optimized by way of simultaneous perceptual quality metric (PQM)
stabilization and entropy maximization for fully automated processing solving
the problem of determination of stopping time. The usage of the HSI or HSV
colour space ensures a unique solution to the optimization problem unlike in
the RGB space where there is none (forcing manual selection of number of
iteration. The proposed approach preserves and enhances details in both bright
and dark regions of underexposed images in addition to eliminating the colour
distortion, over-exposure in bright image regions, halo effect and grey-world
violations observed in Retinex-based approaches. Extensive experiments indicate
consistent performance as the proposed approach exploits and augments the
advantages of PDE-based formulation, performing illumination correction, colour
enhancement correction and restoration, contrast enhancement and noise
suppression. Comparisons shows that the proposed approach surpasses most of the
other conventional algorithms found in the literature.
