1. A method for shading objects in a plurality of images including a first image and a second image comprises: receiving a geometric description of a first object; performing once for both the first image and the second image, a first set of shading operations for the first object in response to the geometric description of the first object; performing a second set of shading operations for the first object in the first image; performing a third set of shading operations for the first object in the second image; combining results of the first set of shading operations for the first object and results of the second set of shading operations for the first object to determine shading values of the first object in the first image; and combining results of the first set of shading operations for the first object and results of the third set of shading operations for the first object to determine shading values of the first object in the second image.