Wavelet-based image fusion for securing multiple images through asymmetric keys

Image fusion is one of the popular methods which provides better quality fused image for interpreting an image data. Discrete wavelet transform based fusion technique is one such method, in which low and high frequency components are merged together to improve the image content. In this paper, we propose this fusion technique for generating asymmetric keys for securing multiple images. An input image to be encrypted is digitally encoded into two phase-only masks employing the principle of optical interference. This process has been repeated for three different input images; however, it can be extended to n images. Now, one of the phase-only masks corresponding to each input image is preserved as a phase key while another set of phase masks are fused together. This fused image is called the encrypted image. Unlike optical asymmetric encryption technique based on amplitude- and phase-truncation approach, here, four asymmetric keys are generated corresponding to each image. Asymmetric keys corresponding to each image, fractional orders, phase-only masks, level of decomposition and type of wavelet, enlarge the key space and hence offer enhanced security. The proposed method is demonstrated through the simulation results.