Image encryption is a useful solution to achieve confidentiality while transmitting digital images over unsecure public networks. Among recently proposed encryption schemes, a DNA-based approach Wei et al. (J. Syst. Softw. 85 (2012) 299) with good encryption effect has been reported. An effort has been made in this paper to improve its performance, by infusing more pseudo randomness into this algorithm. For this, three modifications have been suggested: (1) For each pixel of the color image, adoption of multiple DNA encoding rules as against a single rule in Wei et al. (J. Syst. Softw. 85 (2012) 299); (2) multiple DNA operations instead of a single DNA operation as in [17] for diffusion of pixels and (3) combination of the image to be encrypted with another synthetic image as against combination with itself as in [17]. Here, the choice of DNA encoding rule, DNA operation and DNA synthetic image creation are all done based on the outcome of various chaotic maps and systems. The simulation results and security analysis show that our algorithm not only has a better encryption effect but also has a better ability of resisting statistical and differential attacks on comparison with the original proposal.