Research On Image Lossless Compression And Encryption Algorithm Based On Chaotic System

The increasingly developed Internet has set up higher requirements for the transmission, storage and security of image files. In order to increase the transmission efficiency of the image and reduce the storage space, it is a necessary to compress image files. From the aspects of national security, medical care and satellite remote sensing, image lossless compression is also an essential technology. This paper discusses two different ideological image lossless compression algorithms and makes detailed analysis of them to find suitable e ncryption positions. At last, image lossless compression encryption algorithm is designed.Firstly, the SPIHT lossless image compression and encryption algorithms based on frequency domain transformation are studied. The lifting integer wavelet transformation is selected as the image pixels matrix transformation method to ensure the lossless feature of image compression. During the compression process three different positions are selected as the encryption position for the compression algorithms, including the image wavelet transform matrix, SPIHT sorting and scanning phase and SPIHT compressed stream. All encryption algorithms combine scrambling and diffusion, and the encryption algorithm based on stream cipher is designed based on principles of block cipher. At last, compression efficiency and the safety of these algorithms are analyzed.According to the correlations between the image pixels which result in the redundancy errors, in this paper the CALIC lossless compression and encryption algorithms are studied. The first step pixel values predicted by GAP, the residual feedback, entropy coding and the prediction mode which require the two rows of the original pixels are encrypted respectively. Before the encryption, a new pseudo-random sequence generator based on Lorenz hyper chaotic equation is designed, and the pseudo-random sequences of real numbers are quantized using the random matrix. During the encryption process, an encryption table is designed, and encryption items are selected according to chaotic quantitative sequences. Items in encryption table are related to plaintext, which could increase the security level of the entire encryption system. Finally, the compression efficiency, security and the safety of the pseudo-random sequence generator are analyzed.In this paper, based on the study of two kinds of grayscale image lossless compression and encryption algorithms, encryption algorithms are embedded in a number of positions of compression algorithm, achieving a joint of compression and encryption at the same time. The analysis of experimental results shows that the two different ideas of compression and encryption algorithms have a high security level and better compression performance.