spatstat (version 1.16-0)

opening.owin: Morphological Opening of a Window

Description

Perform morphological opening of a window

Usage

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

Arguments

w

A window (object of class "owin".

r

positive number: the radius of the opening.

...

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 opened window.

Details

The morphological opening (Serra, 1982) of a set $W$ by a distance $r > 0$ is the subset of points in $W$ that can be separated from the boundary of $W$ by a circle of radius $r$. That is, a point $x$ belongs to the opening if it is possible to draw a circle of radius $r$ (not necessarily centred on $x$) that has $x$ on the inside and the boundary of $W$ on the outside. The opened set is a subset of W.

For a small radius $r$, the opening operation has the effect of smoothing out irregularities in the boundary of $W$. For larger radii, the opening operation removes promontories in the boundary. For very large radii, the opened set is empty.

This function computes the opening 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 erode.owin followed by dilate.owin.

References

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

See Also

closing.owin for the opposite operation.

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

Examples

data(letterR)
  v <- opening.owin(letterR, 0.3, dimyx=256)
  plot(v, main="opening.owin")
  plot(letterR, add=TRUE)