threshold.imwd {wavethresh} | R Documentation |
Applies hard or soft thresholding to wavelet decomposition object
of class imwd
.
## S3 method for class 'imwd': threshold(x, levels=3:(x$nlevels-1), type = c("hard", "soft"), policy = c("universal", "manual", "probability"), by.level = FALSE, value = 0, dev = var, verbose = getOption("verbose"), return.threshold = FALSE, compression = TRUE, ...)
x |
object of class "imwd" , typically from a wavelet
decomposition using the imwd function. |
levels |
integer vector determining which levels are thresholded in the decomposition. |
type |
character, determining the type of thresholding; either "hard" or "soft". |
policy |
character indicating the threshold to use, can be "universal", "manual", or "probability". |
by.level |
logical; if FALSE then a global threshold is
applied to all the levels specified by levels ,
otherwise a threshold is computed and applied separately to each level.
|
value |
numeric user-supplied threshold for the "manual"
policy , or the user-supplied quantile level for the
"probability" policy. |
dev |
deviance function. The default var is to use the
variance, but you can insert your own measure of deviance. |
verbose |
logical, if true then threshold() spurts informative
messages at you. |
return.threshold |
logical, if true then the actual threshold is returned, otherwise the thresholded object is returned. |
compression |
logical; if true the thresholded object is compressed and then returned, otherwise it is returned unaltered. |
... |
further arguments to be passed to or from methods. |
Thresholding modifies the coefficients within a imwd
wavelet
decomposition object. The modification can be performed either
with a "hard" or "soft" thresholding selected by the type
argument.
See the ``Details'' section of threshold.wd
for an
explanation of thresholding types and policies.
The thresholding process forces many coefficients to zero. From release 2.2
onwards the thresholded imwd
object is compressed by compress
and returned as a much smaller imwdc
object. An imwdc
object is
easily converted into an imwd
object by uncompress
, but
all relevant functions will handle the imwdc
object.
Note that the coefficients for the horizontal, diagonal and vertical detail at a particular level are treated as one. In future releases we may add the capability to treat the details differently, although this would increase the complexity of the argument specification.
This function is a method for the generic function
threshold()
for class imwd
.
It can be invoked by calling threshold(x)
for an
object x
of the appropriate class, or directly by
calling threshold.imwd(x)
regardless of the
class of the object.
If compression
is true then an object of class "imwdc"
that has been thresholded and compressed,
otherwise an uncompressed, but thresholded object of class "imwd"
.
Release 2.2 Copyright Guy Nason 1993
There should be an optimal policy as well, although universal comes close.
see wd
for a list.
For examples, see imwr.imwd
.
imwr
, imwd
, compress
,
uncompress
, imwd.object
,
imwdc.object