| transformquantiles {spatstat.univar} | R Documentation |
Transform the Quantiles
Description
Apply a transformation to the quantiles of a vector, or to the quantiles of the pixel values in a pixel image.
Usage
transformquantiles(X, uniform = FALSE, reverse = FALSE, ...)
Arguments
X |
A numeric vector, matrix, array, or a pixel image
(object of class |
uniform |
Logical value specifying whether each quantile value should be replaced by the corresponding cumulative probability (called histogram equalisation, transformation to uniformity or probability integral transformation). |
reverse |
Logical value specifying whether to swap the upper and lower quantiles. |
... |
Ignored. |
Details
The argument X may be a vector, matrix,
array, or a pixel image (object of class "im").
The algorithm will first extract the entries or pixel values of
X as a vector, and sort the values into ascending order.
If uniform=TRUE, the entries in this vector will be replaced by the
corresponding cumulative probabilities (the kth
smallest value will be replaced by the
number (k-0.5)/n where n is the total number of values).
If reverse=TRUE, the resulting vector will be reversed
so that it is in descending order (so that the kth smallest
value will be swapped with the kth largest value).
Finally the transformed values will be replaced into the original positions in the vector, matrix, array, or pixel image.
The case uniform=TRUE, reverse=FALSE is called
transformation to uniformity, the
probability integral transformation,
histogram equalisation, or quantile transformation.
The resulting values are uniformly distributed between 0 and 1;
a histogram of the values in X is flat.
Value
Another object of the same type as X.
Author(s)
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner rolfturner@posteo.net and Ege Rubak rubak@math.aau.dk.
See Also
To apply an arbitrary function f to the pixel values in an image,
use the idiom X[] <- f(X[]).
Examples
X <- c(3, 5, 1, 2, 4)
transformquantiles(X, reverse=TRUE)
transformquantiles(X, uniform=TRUE)
transformquantiles(X, uniform=TRUE, reverse=TRUE)