Fig. 1.

Cost functions and choice of threshold. (a) Images of different cost functions. The combination of blue and black lines f₁ denotes the least squares penalty function, the combination of blue and cyan lines f₂ denotes the asymmetric Huber function, the combination of blue and magenta lines f₃ denotes the asymmetric truncated quadratic function, the combination of blue and blue lines f₄ denotes the asymmetric Indec function, and the red dotted line denotes the asymptote of the asymmetric Indec function. (b) Relationship between the noise standard deviation σ and the optimal threshold s. Blue star points denote the optimal threshold s that corresponds to a noise standard deviation σ; the red line is a fitted fourth-order polynomial based on these blue star points. (c) Relationship between threshold s and the up_down_ratio. Red, green, and blue star points denote the up_down_ratio that corresponds to a threshold s. (d) Relationship between the peak ratio and the up_down_ratio. The five polynomial curves denote five simulations, and each curve is fitted using 1000 star points.