Abstract: In pyramidal algorithm, an image is decomposed into multiresolution subbands with sets of tree-structured coefficients.A novel coefficient partition algorithm is introduced to split coefficients into two sets using a spatial orientation tree data structure.By splitting the coefficients, the overall theoretical entropy is reduced due to the different probability distribution for the two coefficient sets.A lossless coder based on the algorithm has a better performance than other wavelet-based lossless coders in our experiments.