Abstract: To ensure the security application of images with special format,it is necessary to conduct an in-depth study of the corresponding image encryption algorithm compatible with its format.By integrating JPEG compression and the idea of self-adaptive encryption,a self-adaptive encryption algorithm for JPEG color image was proposed.DC coefficients and the first 16 AC coefficients in Zig-Zag order of JPEG compression are chosen to construct the corresponding matrices.Based on chaotic random sequence,self-adaptive encryption scheme is utilized to encrypt the coefficients,and the sign of DC coefficients is also encrypted to avoid color information leaking.Experimental results and analyses verify that both the security and performance of the proposed algorithm are good,and the impact on the compression is negligible.Furthermore,it is compatible with JPEG file format.

Key words: JPEG color image,Encryption,Format compatibility,Security