Application of additional input amplitude masks in schemes of optical image encryption with spatially incoherent illumination

Application of additional input amplitude masks in schemes of optical image encryption with spatially incoherent illumination is proposed. The masks are used for increasing the signal-to-noise ratio in decrypted images and enhancing the security of encrypted images. Two kinds of additional input amplitude masks were developed and tested. The first one is a rectangular grating mask. Its application results in duplications of the original image spectrum at high spatial frequencies corresponding to mask’s frequency. The second one is a random mask. Its application results in the distribution of each component of the original image spectrum throughout the entire Fourier spectrum. Computer simulations of optical encryption with spatially incoherent illumination and additional input amplitude masks were performed. Increase in signal-to-noise ratio of $>2$ times was achieved, as well as attaining the enhanced security of the encrypted image.