I like that paper, but I don’t think it was the first to suggest separating x and y and using multi-pass for distance transforms. Here are a few that predate a

I like that paper, but I don’t think it was the first to suggest separating x and y and using multi-pass for distance transforms. Here are a few that predate and I think make the same observation: https://dl.acm.org/doi/10.1016/j.ipl.2006.12.005 https://dl.acm.org/doi/10.1016/j.ipl.2006.12.005 https://www.sciencedirect.com/science/article/abs/pii/002001909600049X https://www.sciencedirect.com/science/article/abs/pii/002001... That second paper from 1996 references an even older paper from 94, saying “Dividing rows and columns alternately, Chen and Chuang reduced the time complexity to O(N^2) which is optimal.” https://www.sciencedirect.com/science/article/abs/pii/002001909400062X https://www.sciencedirect.com/science/article/abs/pii/002001...