@article {SHISPL, title = {Rotational Invariant Operators based on Steerable Filter Banks}, journal = {IEEE Signal Processing Letters}, volume = {13}, number = {11}, year = {2006}, url = {http://users.soe.ucsc.edu/~manduchi/papers/SPpaperRV-2cols.pdf}, author = {X. Shi and Ribeiro-Castro, A.L. and Roberto Manduchi and R. Montgomery} }