Time-Frequency-Plane Plot
DESCRIPTION:
Plots the modulus of the coefficients from a wavelet packet or cosine packet transform in the time-frequency plane.

This function is generic (see Methods); method functions can be written to handle specific classes of data. Classes which already have methods for this function include:

cp.molecule, cpt, dwt, nd.dwt, rob.dwt, wp.molecule, wpt.

USAGE: 
time.freq.plot(x, plot=T, power.stretch=0, ...)
time.scale.plot(x, plot=T, power.stretch=0, ...)
REQUIRED ARGUMENTS:
x:
an S-PLUS object inheriting from one of the classes above.
OPTIONAL ARGUMENTS:
plot:
if TRUE, a time-frequency plane plot will be provided.
power.stretch:
a numeric value giving the power of the transform if stretch.image is TRUE. If power.stretch=0, then image is transformed with log(abs(x)+1). Otherwise, the image is transformed with (abs(x))^power.stretch.
...:
additional arguments acceptable to image.
VALUE:
a list with the components: x, y and z suitable for input to image.
SIDE EFFECTS:
an image is created.
DETAILS:
A time-frequency plane plot is also known as the "scalogram" (when based on the wavelet transform) and the "spectrogram" (when based on the Fourier transform). It plots the modulus of the coefficients as rectangles (known as Heisenberg boxes) in the time-frequency plane. The center of each rectangle is determined by the functions center and freq.center. The area of each rectangle is the same with the width and height given by the functions bandwidth and freq.bandwidth.
REFERENCES:
Coifman, R., Meyer, Y., Quake, S. and Wickerhauser, M. V. (1990). Signal processing and compression with wavelet packets. Technical report, Yale University.
SEE ALSO:
cpt , tree.plot , wpt .
EXAMPLES: 
xx <- make.signal("linchirp", 512)
ww <- wp.table(xx, wavelet="s8")
bb <- best.basis(ww)          # select the best basis
time.freq.plot(bb)            # time-frequency plane plot for the best basis


ww.dwt <- as.dwt(ww)          # extract DWT coefficients from the full table
time.freq.plot(ww.dwt)        # time-frequency plane plot for DWT