In this paper, a chaotic image encryption scheme with an efficient permutation–diffusion mechanism is constructed, where six generalized Bernoulli shift maps and one six-dimensional Arnold map are utilized to generate one hybrid chaotic orbit applied to disorder the pixel positions in the permutation process while four generalized Bernoulli shift maps and one Arnold map are employed to yield two random gray value sequences to change the gray values by a two-way diffusion process. Several merits of the proposed image encryption scheme are achieved, including a huge key space, good statistical properties resisting statistical attack and differential attack, desirable robustness against malicious attacks on cipher-images, such as cropping, noising, JPEG compression, etc. Experimental results have been carried out with detailed analysis to show that the proposed scheme can be a potential candidate for practical image encryption.