A new geometrical optical method has been developed for the design of optical systems that perform intensity reshaping of spatially coherent input light, particularly that of plane parallel or spherical beams. The computation is based on the principle of automated optimization, making it available for the design of beam shapers of diverse structures (aspheric, diffractive, etc.), and especially for those where no analytic solution exists to calculate the necessary device geometry (e.g., in case of all-spherical systems). Novelty, and thus efficiency, of the method lies in its simplified definition of the error function, used for the evaluation of optical systems by optimization algorithms during the design process. Another advantage of the method is that it can be easily implemented in commercially available optical design programs commonly used by optical designers. The operation of the new method is shown for the particular case of Gaussian-to-uniform beam transforming systems, and a concrete design example is given for its application. Wave-optical calculations verify the accuracy of our computations and check the diffraction behavior of the geometrically designed device.