In this paper, we present efficient six-connected contour coding algorithms which can uniquely reconstruct any contour image and efficiently compress the contour data. We first design chain difference codes using two onward direction states, based on the fact that the probability distribution of the direction vectors of horiwntal/vertical direction state is different from that of the direction vectors of diagonal direction state. In order to increase coding efficiency, we also design chain difference codes using five states which are classified according to current and previous onward direction vectors. In addition, we also remove the END codeword to reduce total codeword occurrency. Experimental results show that when using 2 states and 5 states without END codeword total entropy decreases by about 12% and 14% for real images and by about 10% and 26% for a synthetic image, respectively.