filter.select {wavethresh} | R Documentation |
This function stores the filter coefficients necessary for doing a discrete wavelet transform (and its inverse).
filter.select(filter.number, family="DaubLeAsymm", constant=1)
filter.number |
This selects the desired filter, an integer that takes a value dependent upon the family that you select. |
family |
This selects the basic family that the wavelet comes from. The choices are DaubExPhase for Daubechies' extremal phase wavelets, DaubLeAsymm for Daubechies' ``least-asymmetric'' wavelets, bolf{Lawton} for Lawton's complex-valued wavelets, LittlewoodPaley for a bad approximation to Littlewood-Paley wavelets. |
constant |
This constant is applied as a multiplier to all the coefficients. It can be a vector, and so you can adapt the filter coefficients to be whatever you want. (This is feature of negative utility, or ``there is less to this than meets the eye'' as my old PhD supervisor would say [GPN]). |
This function contains at least three types of filter. Two types can be selected with family set to DaubExPhase, these wavelets are the Haar wavelet (selected by filter.number=1 within this family) and Daubechies ``extremal phase'' wavelets selected by filter.numbers ranging from 2 to 10). Setting family to DaubLeAsymm gives you Daubechies least asymmetric wavelets, but here the filter number ranges from 4 to 10. For Daubechies wavelets, filter.number corresponds to the N of that paper, the wavelets become more regular as the filter.number increases, but they are all of compact support.
Setting family equal to ``Lawton'' chooses complex-valued wavelets. The only wavelet available is the one with ``filter.number'' equal to 3.
The function compare.filters
can be used to compare two filters.
Alist is returned with four components describing the filter:
H |
A vector containing the filter coefficients. |
G |
A vector containing filter coefficients (if Lawton wavelets are selected, otherwise this is NULL). |
name |
A character string containing the name of the filter. |
family |
A character string containing the family of the filter. |
filter.number |
The filter number used to select the filter from within a family. |
Version 3.5.3 Copyright Guy Nason 1994
The (Daubechies) filter coefficients should always sum to sqrt(2). This is a useful check on their validity.
wd
, wr
, wr.wd
, accessC
, accessD
, compare.filters
, imwd
, imwr
, threshold
, draw
.
#This function is usually called by others. However, on occasion you may wish to look at the coefficients themselves. # # look at the filter coefficients for N=4 (by default Daubechies' # least-asymmetric wavelets.) # #filter.select(4) #$H: #[1] -0.07576571 -0.02963553 0.49761867 0.80373875 0.29785780 #[6] -0.09921954 -0.01260397 0.03222310 # #$G: #NULL # #$name: #[1] "Daub cmpct on least asymm N=4" # #$family: #[1] "DaubLeAsymm" # #$filter.number: #[1] 4