Multiple-image encryption using spectral cropping and spatial multiplexing

A multiple-image encryption scheme is proposed using spectral cropping and space multiplexing based on discrete multiple-parameter fractional Fourier transform (DMPFRFT). Spectrum of each original image is firstly cropped by a low-pass filter, and the image is then recovered with the same size of the filter. The recovered images are spatially shifted and multiplexed into a complex signal with the same size of original image. The complex signal is multiplied by a pixel scrambling operation and random phase mask, and then encrypted into one image by DMPFRFT. The multiplexing images can be retrieved with correct keys, and the original images can be then obtained by enlarging the demultiplexing images. Numerical simulations have been done to demonstrate the validity and the security of the proposed method.