remove vignetting effects
Vignetting Reducer can help you reduce or remove the effects of vignetting from a photograph, often caused by the mechanical properties of the lens, wrongly aligned filters or hood attachment. The program uses a process that involves the taking of a second picture using a bright background with the same lens, filters and hood that caused the initial vignetting effect. You can then load the second image as a mask and further adjust the effect and brightness until the vignetting effect is reduced or removed. Can produce good results, but involves some effort.