# 3D transform¶

In the examples below I assume you’ve imported pyplot and numpy and, of course, the dtcwt library itself:

import numpy as np
from matplotlib.pyplot import *
from dtcwt import *


We can demonstrate the 3D transform by generating a 64x64x64 array which contains the image of a sphere:

GRID_SIZE = 64
SPHERE_RAD = int(0.45 * GRID_SIZE) + 0.5

grid = np.arange(-(GRID_SIZE>>1), GRID_SIZE>>1)
X, Y, Z = np.meshgrid(grid, grid, grid)
r = np.sqrt(X*X + Y*Y + Z*Z)

sphere = 0.5 + 0.5 * np.clip(SPHERE_RAD-r, -1, 1)


If we look at the central slice of this image, it looks like a circle:

imshow(sphere[:,:,GRID_SIZE>>1], interpolation='none', cmap=cm.gray)


Performing the 3 level DT-CWT with the defaul wavelet selection is easy:

Yl, Yh = dtwavexfm3(sphere, 3)


The function returns the lowest level low pass image and a tuple of complex subband coefficients:

>>> print(Yl.shape)
(16, 16, 16)
>>> for subbands in Yh:
...     print(subbands.shape)
(32, 32, 32, 28)
(16, 16, 16, 28)
(8, 8, 8, 28)


Performing the inverse transform should result in perfect reconstruction:

>>> Z = dtwaveifm3(Yl, Yh)
>>> print(np.abs(Z - ellipsoid).max()) # Should be < 1e-12
8.881784197e-15


If you plot the locations of the large complex coefficients, you can see the directional sensitivity of the transform:

from mpl_toolkits.mplot3d import Axes3D

figure(figsize=(16,16))
nplts = Yh[-1].shape[3]
nrows = np.ceil(np.sqrt(nplts))
ncols = np.ceil(nplts / nrows)
W = np.max(Yh[-1].shape[:3])
for idx in xrange(Yh[-1].shape[3]):
C = np.abs(Yh[-1][:,:,:,idx])
ax = gcf().add_subplot(nrows, ncols, idx+1, projection='3d')
ax.set_aspect('equal')
good = C > 0.2*C.max()
x,y,z = np.nonzero(good)
ax.scatter(x, y, z, c=C[good].ravel())
ax.auto_scale_xyz((0,W), (0,W), (0,W))

tight_layout()


For a further directional sensitivity example, see Showing 3D Directional Sensitivity.