R: Level Set of a Pixel Image

levelset {spatstat} | R Documentation

## Level Set of a Pixel Image

### Description

Given a pixel image, find all pixels which have values less than a specified threshold value (or greater than a threshold, etc), and assemble these pixels into a window.

### Usage

      levelset(X, thresh, compare="<=")

### Arguments

`X` | A pixel image (object of class "im")

.

`thresh` | Threshold value. A single number or value compatible with the pixel values in `X`

.

`compare` | Character string specifying one of the comparison operators `"<", ">", "==", "<=", ">=", "!="`.

### Details

If `X` is a pixel image with numeric values, then `levelset(X, thresh)` finds the region of space where the pixel values are less than or equal to the threshold value `thresh`. This region is returned as a spatial window.

The argument `compare` specifies how the pixel values should be compared with the threshold value. Instead of requiring pixel values to be less than or equal to `thresh`, you can specify that they must be less than (`<`), greater than (`>`), equal to (`==`), greater than or equal to (`>=`), or not equal to (`!=`) the threshold value `thresh`.

If `X` has non-numeric pixel values (for example, logical or factor values) it is advisable to use only the comparisons `==` and `!=`, unless you really know what you are doing.

For more complicated logical comparisons, see `solutionset`.

### Value

A spatial window (object of class `"owin"`, see `owin.object`) containing the pixels satisfying the constraint.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

and Rolf Turner r.turner@auckland.ac.nz

### See Also

`im.object`, `as.owin`, `solutionset`.

### Examples

      # test image
      X <- as.im(function(x,y) { x^2 - y^2 }, unit.square())

      W <- levelset(X, 0.2)
      W <- levelset(X, -0.3, ">")

      # compute area of level set
      area(levelset(X, 0.1))

[Package spatstat version 1.63-3 Index]