Implementation of gray image encryption with pixel shuffling and gray-level encryption by single chaotic system

When the grays of images present a strong contrast, merely encrypting the gray-level of image pixels is unable to eliminate the image outlines. The adoption of pixel shuffling can eliminate the image outlines, but cannot disrupt the characteristics of gray-level spectrum. Since a chaotic system is highly sensitive to the initial values and the chaotic trajectory is unpredictable, the application of this method to communication encryption and decryption renders a high level of security. In this paper, the chaotic system is adopted as the fundamental base and combined with row, column shuffling, and gray-level encryption to not only eliminate image outlines, but also disrupt the distributional characteristics of gray level, and the resulting increases of key space. Various statistical methods, such as correlation coefficient, NPCR (Number of Pixels Change Rate), UACI (Unified Average Changing Intensity), and entropy, provide analysis of the efficacy of the encryption method proposed. Our example reveals that the proposed encryption method can obtain highly secure encrypted images.