Introduction . Recently, optical techniques1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11in image encryption have been intensely studied, owing to their inherent superiority with respect to multiple parameters and parallel processing. The pioneering work of optical image encryption is on double-random phase encoding (DRPE)12, which is done on the Fourier transform domain. Several works that followed have reported the expansion of initial DRPE work into differ...