@inproceedings{ritschel2008imperfectillumination,
 author = {Ritschel T, Grosch T, Kim MH, Seidel HP, Dachsbacher C, Kautz J},
 title = {Imperfect shadow maps for efficient computation of indirect illumination},
 year = {2008},
 booktitle = {ACM Transactions on Graphics},
}