@conference {uvigo:hexagonal, title = {Hexagonal Quantizers are not Optimal for 2-D Data Hiding}, booktitle = {Security and Watermarking of Multimedia Contents}, series = {Proc. of SPIE}, volume = {5020}, year = {2003}, month = {jan}, address = {Santa Clara, USA}, keywords = {data-hiding, watermarking}, author = {F{\'e}lix Balado and Fernando P{\'e}rez-Gonz{\'a}lez}, editor = {Ping W. Wong and Edward J. Delp} }