Abstract: Indirect illumination plays an important role in global illumination. However, computing indirect illumination is a time-consuming process and needs to be approximated to achieve interactive performance. Indirect illumination varies rather slowly across the surface. This leads to the idea of computing indirect illumination sparsely in the scene and interpolating the result. This paper presents a hierarchical structure, which enables efficient sampling. The hierarchy is constructed in the image space by exploiting coherences among the screen-space pixels. From the hierarchy, samples are chosen, each of which represents a group of coherent pixels. This paper presents two methods of utilizing the samples for indirect lighting computation. The methods produce plausible lighting results and show high performances. The proposed algorithms run entirely in the image space and are easy to implement in contemporary graphic hardware.