This paper reports the last part of a study on the drop size distribution of sprays produced by high-pressure swirl atomizers dedicated to gasoline direct injection. This last part focuses on the deconvolution of line-of-sight forward diffraction measurements of the spray drop size distribution in order to understand the variation of the mean drop diameter D 43 in the head of the spray. First, the spatial resolution of the deconvolution technique is improved by developing a continuous deconvolution procedure. Second, this new procedure is applied on a series of four GDI injectors. The results show that the variation of the mean diameter D 43 in the head of the spray is related to the presence of the pre-spray. Furthermore, the deconvolution technique allowed the determination of the pre-spray drop size distribution. It is found that the pre-spray drops are still a problem in GDI application and that there are very much a function of the injector geometry.