An image processing apparatus comprises data receiving circuitry for receiving a volumetric imaging data set which is representative of a volume, the volume comprising a region of interest and lighting circuitry configured to place a virtual light source outside the region of interest and to apply a lighting simulation process to simulate light from the virtual light source. The applying of the lighting simulation process is at least partially different for a first lighting region than for a second lighting region, the first lighting region comprising at least part of the volume outside the region of interest and the second lighting region comprising at least part of the region of interest.