Optical multi-image encryption scheme based on discrete cosine transform and nonlinear fractional Mellin transform

A new multi-image encryption scheme with an optical implementation based on the nonlinear fractional Mellin transform is proposed, which could avoid the vulnerability of the linear encryption systems and encrypt multiple images simultaneously. In the proposed scheme, the original images are transformed into spectra by the discrete cosine transform, then the spectra are incised and spliced into a composite spectrum, and finally the composite spectrum is performed by the nonlinear fractional Mellin transform to obtain the final encrypted image. After the processing of the fractional Mellin transform, amplitude encoding and phase encoding are adopted. The orders of the fractional Mellin transform are the main keys of this multi-image encryption scheme. Simulation results demonstrate the validity and the security of the proposed scheme.