Chaos has been given much consideration as a feasible image encryption technique in current research. Nevertheless, some chaotic sequences can be reconstructed precisely owing to the finite computational precision. The focus of the work presented in this paper is to incorporate permutation and substitution methods, to present a strong image encryption algorithm. An optimized treatment and a cross-sampling disposal are introduced for enhancing the irregular and pseudorandom characteristics of chaotic sequences. Its design and implementation has been detailedly discussed and tested. Through simulation and analysis, the favorable performances of the proposed algorithm are evaluated.