Halftone image encryption based on reversible pairwise swapping

• Motivation, principle and realization details of a halftone image encryption technique.
• A systematic introduction for reversible pairwise swapping and applications.
• The method is also applicable for binary image encryption.
• Extensive experiments for testing the effectiveness and efficiency.

As a special kind of binary image, halftone image is produced by digital halftoning and widely used in printing. In recent years, some consumer electronics apply halftone image for lost-cost liquid crystal display systems. However, few techniques are reported for securing the content of halftone images, although a variety of schemes have been developed for continuous-tone image encryption in literatures. This paper proposes an encryption scheme for digital halftone images based on the principle of reversible pairwise swapping. The encryption and decryption phases are symmetrical because of the reversibility. It also can be easily integrated into some emerging display technologies such as cholesteric liquid crystal display which is used in electronic paper book. This secure method is also applicable for binary image encryption. Extensive experimental results demonstrate the effectiveness and efficiency of the proposed method.