In this paper, we propose to improve the security performance of a recently proposed color image encryption algorithm which is based on multi-chaotic systems. The existing cryptosystem employed a pixel-chaotic-shuffle mechanism to encrypt images, in which the generation of shuffling sequences are independent to the plain-image/cipher-image. As a result, it fails to the chosen-plaintext and known-plaintext attacks. Moreover, the statistical features of the cryptosystem are not up to the standard. Therefore, the security improvements are framed to make the above attacks infeasible and enhance the statistical features as well. It is achieved by modifying the pixel-chaotic-shuffle mechanism and adding a new pixel-chaotic-diffusion mechanism to it. The keys for diffusion of pixels are extracted from the same chaotic sequences generated in the previous stage. The simulation analyses and studies are performed to demonstrate that the updated version of cryptosystem has better statistical features and resistant to the chosen-plaintext and known-plaintext attacks than the existing algorithm.