“…Since the foreground F , background B, and alpha matte 𝛼 are unknown, only the observed image I is known, image matting is an ill-defined problem. To address this problem, most existing methods [3,5,8,12,13,15,19,25,26,28,41,44,45] need a trimap to indicate the known foreground and background regions and unknown regions in the image, which can be roughly categorized into sampling-based methods, propagation-based methods, and learning-based methods. Sampling-based methods [2,9,12,15,31,36,41] select the best foreground and background color pairs in the known regions for the each pixel in unknown regions to estimate the alpha values based on assumptions on color association.…”