In this study we propose two new methods, namely iso-transmission line and subregion direct approximation methods, for dual energy image decomposition calculations. These two methods are compared with two other conventional techniques, i.e. non-linear equations and direct approximation. The computation accuracy, sensitivity to quantum noise and efficiency are used as indicesf or comparison. Both the subregion direct approximation method and the iso-transmission line method give better accuracy than the two conventional methods. The iso-transmission line, direct approximation and subregion methods are computationally more efficient than the non-linear equations method. The image calculated by the iso-transmission line and the subregion methods are more sensitive to noise.