Chessboard distance transform?

[Gabriel Landini]

Hi
I wonder if anybody has implemented a chessboard or Chebyshev distance
transform that does not treat the borders of the image as foreground.
I realise that IJ comes with its own EDM built in IJ, but I want specifically
the chessboard distance. Computing it with sequential dilations seems very
inefficient and I wonder if anybody has some quicker implementation.

Thanks for any pointers.
Cheers

Gabriel

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