Nobuyuki Otsu (1979). "A Threshold Selection Method from Gray-Level Histograms". IEEE Transactions on Systems, Man, and Cybernetics. 9 (1): 62–66. doi:10.1109/TSMC.1979.4310076.
Ridler TW dan Calvard S (1978). "Picture Thresholding Using an Iterative Selection Method". IEEE Transactions on Systems, Man, and Cybernetics. 8 (8): 630–632. doi:10.1109/TSMC.1978.4310039.Pemeliharaan CS1: Menggunakan parameter penulis (link)
