1. A volume rendering process based on casting rays in a volume data set, wherein the process is designed to run on a computer system including a processing unit with a SIMD architecture, the process comprising: arranging the rays into different ray tiles according to a prediction of the amount of processing needed to render each ray or ray segment; performing rendering on each of the ray tiles in the processing unit to create an intermediate rendered image; and transforming the intermediate rendered image by permuting the intermediate image to a correct rendered image.