Basic plotting of wavelet analysis output in matplotlib

Question

I am discovering wavelets in practice thanks to the python module pywt.

I have browsed some examples of the pywt module usage, but I could not grasp the essential step:

Answer 1

You should extract the different 1D series from your array of interest, and use matplotlib as in most simple example

import matplotlib.pyplot as plt
plt.plot([1,2,3,4])
plt.ylabel('some numbers')
plt.show()

from doc.

You wish to superimpose 1D plots (or line plots). So, if you have lists l1, l2, l3, you will do

import matplotlib.pyplot as plt
plt.plot(l1)
plt.plot(l2)
plt.plot(l3)
plt.show()

For a scalogram: what i used was imshow(). This was not for wavelets, but same ID: a colormap.

I have found this sample for use of imshow() with wavelets, didn t try thought

from pylab import *
import pywt
import scipy.io.wavfile as wavfile

# Find the highest power of two less than or equal to the input.
def lepow2(x):
    return 2 ** floor(log2(x))

# Make a scalogram given an MRA tree.
def scalogram(data):
    bottom = 0

    vmin = min(map(lambda x: min(abs(x)), data))
    vmax = max(map(lambda x: max(abs(x)), data))

    gca().set_autoscale_on(False)

    for row in range(0, len(data)):
        scale = 2.0 ** (row - len(data))

        imshow(
            array([abs(data[row])]),
            interpolation = 'nearest',
            vmin = vmin,
            vmax = vmax,
            extent = [0, 1, bottom, bottom + scale])

        bottom += scale

# Load the signal, take the first channel, limit length to a power of 2 for simplicity.
rate, signal = wavfile.read('kitten.wav')
signal = signal[0:lepow2(len(signal)),0]
tree = pywt.wavedec(signal, 'db5')

# Plotting.
gray()
scalogram(tree)
show()