levelset
Level Set of a Pixel Image
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.
- Keywords
- manip, spatial, programming
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", seeowin.object) containing the pixels satisfying the constraint.
See Also
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.owin(levelset(X, 0.1))