By merging or adding the color contributions from objects intersected by secondary rays, the image processing system may accumulate color contributions to pixels from objects intersected by secondary rays as the further color contributions are determined. Furthermore, by associating a scaling factor of color contribution with objects and with secondary rays which intersect the objects, color contributions due to secondary ray/object intersections may be calculated at a later time than the color contribution to a pixel from original ray/object intersection. Consequently, it is not necessary for a vector throughput engine or a workload manager to wait for all secondary ray/object intersections to be determined before updating the color of a pixel.