Recursive implementation of erosions and dilations along discrete lines at arbitrary angles

Van Herk (1992) has shown that the erosion/dilation operator with a linear structuring element of an arbitrary length can be implemented in only three min/max operations per pixel. In this paper, the algorithm is generalized to erosions and dilations along discrete lines at arbitrary angles. We also address the padding problem; so that the operation can be performed in place without copying the pixels to and from an intermediate buffer. Applications to image filtering and to radial decompositions of discs are presented.