Research Of Image Compression-Encryption Algorithm Based On The Improved JPEG-LS

In recent years, with the rapid development of digital image and network technology, people’s requirements for image quality is more and more stringent. The images which people require are not only high reconstructed image quality but also not be disclosed during transmission of information, which needs compression and encryption for image. The continuous-tone still images lossless or near-lossless compression standard (Joint Photographic Experts Group-lossless Standard, JPEG-LS) has excellent performance in lossless/near-lossless compression. The key sequence that chaotic system generated has better confidentiality. The two together both improve the transmission efficiency of image data, but also ensure that the data transfer is not compromised.In order to solve the problem that traditional image compression ratio control is not fine and low dimension chaotic system security is not high, this paper proposes an encryption algorithm based on compressed ratio control. On the basis of in-depth analysis about the distortion control parameters Near of JPEG-LS algorithm which has significant influence on the image compression ratio and image quality, the image data of raster scan was first gradient processed in causal model, the size of the gradient value and then Near were compared to determine to enter run mode or normal mode, random processing sequence generated by three-dimensional Lorenz chaos system was regard as key to encrypt in run mode, conventional model and whole model(run and conventional model). Finally, Confirm Near subscript value by comparing the block real-time compression ratio and the target compression ratio and query the initial Near value in the next sub-block through the subscript value. The image compression ratio fine control and improving the confidentiality were realized by means of dynamic adjusting Near in real time. The proposed algorithm has both a good performance on control of the compression ratio, and its quality of reconstruction image is improved about by0.5dB than linear compression ratio control algorithm. What’s more, it has high security that can resist entropy attack, differential attack, brute force attack and statistical attack et al., and the encryption has no effect on the compression efficiency.