spatstat (version 1.16-0)

closing.owin: Morphological Closing of a Window

Description

Perform morphological closing of a window

Usage

closing.owin(w, r, ..., polygonal=TRUE)

Arguments

w

A window (object of class "owin".

r

positive number: the radius of the closing.

...

extra arguments passed to as.mask controlling the pixel resolution, if a pixel approximation is used

polygonal

Logical flag indicating whether to compute a polygonal approximation to the erosion (polygonal=TRUE) or a pixel grid approximation (polygonal=FALSE).

Value

• Another object of class "owin" representing the closed window.

Details

The morphological closing (Serra, 1982) of a set $W$ by a distance $r > 0$ is the set of all points that cannot be separated from $W$ by any circle of radius $r$. That is, a point $x$ belongs to the closing $W*$ if it is impossible to draw any circle of radius $r$ that has $x$ on the inside and $W$ on the outside. The closing $W*$ contains the original set $W$.

For a small radius $r$, the closing operation has the effect of smoothing out irregularities in the boundary of $W$. For larger radii, the closing operation smooths out concave features in the boundary. For very large radii, the closed set $W*$ becomes more and more convex.

This function computes the closing of the window w as a binary pixel mask. If w is not already a mask, it is first converted to a mask by as.mask. The arguments "..." determine the pixel resolution. There is a sensible default.

The algorithm simply applies dilate.owin followed by erode.owin.

References

Serra, J. (1982) Image analysis and mathematical morphology. Academic Press.

See Also

opening.owin for the opposite operation.

dilate.owin, erode.owin for the basic operations. owin, as.owin for information about windows.

Examples

data(letterR)
  v <- closing.owin(letterR, 0.25, dimyx=256)
  plot(v, main="closing.owin")
  plot(letterR, add=TRUE)