In this paper, we focus on another issue. That is how to determine the optimal side information, i.e., combination of peak and zero bins, associated with the least distortion for the given payload. According to our understanding, the optimal selection of peak and zero bins could be modeled as an optimization problem as shown in (9), in which the fewer constraints are offered, the more flexible search is performed in a larger solution space. As a result, a better solution could be achieved in theory. Herein, based on search flexibility and the number of constraints in the optimization model, recent schemes could be simply summarized into three levels in this paper.