04. Image deblurring

Deblurring is the process of removing blurring effects from images, caused for example by defocus aberration or motion blur.

In forward mode, such blurring effect is typically modelled as a 2-dimensional convolution between the so-called point spread function and a target sharp input image, where the sharp input image (which has to be recovered) is unknown and the point-spread function can be either known or unknown.

In this tutorial, an example of 2d blurring and deblurring will be shown using the pylops.signalprocessing.Convolve2D operator assuming knowledge of the point-spread function.

import numpy as np
import matplotlib.pyplot as plt
import pylops

Let’s start by importing a 2d image and defining the blurring operator

im = np.load('../testdata/python.npy')[::5, ::5, 0]

Nz, Nx = im.shape

# Blurring guassian operator
nh = [15, 25]
hz = np.exp(-0.1*np.linspace(-(nh[0]//2), nh[0]//2, nh[0])**2)
hx = np.exp(-0.03*np.linspace(-(nh[1]//2), nh[1]//2, nh[1])**2)
hz /= np.trapz(hz) # normalize the integral to 1
hx /= np.trapz(hx) # normalize the integral to 1
h = hz[:, np.newaxis] * hx[np.newaxis, :]

fig, ax = plt.subplots(1, 1, figsize=(5, 3))
him = ax.imshow(h)
ax.set_title('Blurring operator')
fig.colorbar(him, ax=ax)
ax.axis('tight')

Cop = pylops.signalprocessing.Convolve2D(Nz * Nx, h=h,
                                         offset=(nh[0] // 2,
                                                 nh[1] // 2),
                                         dims=(Nz, Nx), dtype='float32')
../_images/sphx_glr_deblurring_001.png

We will now apply the blurring operator to the sharp image. Finally we try to recover the sharp input image by inverting the convolution operator from the blurred image. Note that when we perform inversion without any regularization, the deblurred image will show some ringing due to the instabilities of the inverse process. Adding TV regularization allows to recover sharp contrasts.

imblur = Cop * im.flatten()

imdeblur = \
    pylops.optimization.leastsquares.NormalEquationsInversion(Cop, None,
                                                              imblur,
                                                              maxiter=50)

Dop = [pylops.FirstDerivative(Nz * Nx, dims=(Nz, Nx), dir=0, edge=False),
       pylops.FirstDerivative(Nz * Nx, dims=(Nz, Nx), dir=1, edge=False)]
imdeblurtv = \
    pylops.optimization.sparsity.SplitBregman(Cop, Dop, imblur.flatten(),
                                              niter_outer=10, niter_inner=5,
                                              mu=1.5, epsRL1s=[1e0, 1e0],
                                              tol=1e-4, tau=1., show=False,
                                              ** dict(iter_lim=5, damp=1e-4))[0]

# Reshape images
imblur = imblur.reshape((Nz, Nx))
imdeblur = imdeblur.reshape((Nz, Nx))
imdeblurtv = imdeblurtv.reshape((Nz, Nx))

Finally we visualize the original, blurred, and recovered images.

# sphinx_gallery_thumbnail_number = 2
fig = plt.figure(figsize=(8, 5))
fig.suptitle('Deblurring', fontsize=14, fontweight='bold', y=0.95)
ax1 = plt.subplot2grid((2, 4), (0, 0))
ax2 = plt.subplot2grid((2, 4), (0, 1))
ax3 = plt.subplot2grid((2, 4), (1, 0))
ax4 = plt.subplot2grid((2, 4), (1, 1))
ax5 = plt.subplot2grid((2, 4), (0, 2), colspan=2)
ax6 = plt.subplot2grid((2, 4), (1, 2), colspan=2)
ax1.imshow(im, cmap='viridis', vmin=0, vmax=250)
ax1.axis('tight')
ax1.set_title('Original')
ax2.imshow(imblur, cmap='viridis', vmin=0, vmax=250)
ax2.axis('tight')
ax2.set_title('Blurred')
ax3.imshow(imdeblur, cmap='viridis', vmin=0, vmax=250)
ax3.axis('tight')
ax3.set_title('Deblurred')
ax4.imshow(imdeblurtv, cmap='viridis', vmin=0, vmax=250)
ax4.axis('tight')
ax4.set_title('TV deblurred')
ax5.plot(im[Nz//2], 'k')
ax5.plot(imblur[Nz//2], '--r')
ax5.plot(imdeblur[Nz//2], '--b')
ax5.plot(imdeblurtv[Nz//2], '--g')
ax5.axis('tight')
ax5.set_title('Horizontal section')
ax6.plot(im[:, Nx//2], 'k', label='Original')
ax6.plot(imblur[:, Nx//2], '--r', label='Blurred')
ax6.plot(imdeblur[:, Nx//2], '--b', label='Deblurred')
ax6.plot(imdeblurtv[:, Nx//2], '--g', label='TV deblurred')
ax6.axis('tight')
ax6.set_title('Vertical section')
ax6.legend(loc=5, fontsize='small')
plt.tight_layout()
plt.subplots_adjust(top=0.8)
../_images/sphx_glr_deblurring_002.png

Total running time of the script: ( 0 minutes 2.949 seconds)

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