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))