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Jostein Bø Fløystad
63 lines
1.7 KiB
Python
63 lines
1.7 KiB
Python
"""
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================
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Phase Unwrapping
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================
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Some signals can only be observed modulo 2*pi, and this can also apply to
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two- and three dimensional images. In these cases phase unwrapping is
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needed to recover the underlying, unwrapped signal. In this example we will
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demonstrate an algorithm [1]_ implemented in ``skimage`` at work for such a
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problem.
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"""
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import numpy as np
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from matplotlib import pyplot as plt
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from skimage import data, img_as_float, color, exposure
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# Load an image as a floating-point grayscale
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image = color.rgb2gray(img_as_float(data.chelsea()))
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# Scale the image to [0, 4*pi]
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image = exposure.rescale_intensity(image, out_range=(0, 4 * np.pi))
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# Create a phase-wrapped image in the interval [-pi, pi)
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image_wrapped = np.angle(np.exp(1j * image))
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# Perform phase unwrapping
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image_unwrapped = exposure.unwrap(image_wrapped)
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# Plotting
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plt.figure()
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plt.subplot(221)
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plt.title('Original')
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plt.imshow(image, cmap='gray', vmin=0, vmax=4 * np.pi)
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plt.colorbar()
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plt.subplot(222)
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plt.title('Wrapped phase')
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plt.imshow(image_wrapped, cmap='gray', vmin=-np.pi, vmax=np.pi)
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plt.colorbar()
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plt.subplot(223)
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plt.title('After phase unwrapping')
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plt.imshow(image_unwrapped, cmap='gray')
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plt.colorbar()
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plt.subplot(224)
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plt.title('Unwrapped minus original')
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plt.imshow(image_unwrapped - image, cmap='gray')
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plt.colorbar()
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plt.show()
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"""
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.. image:: PLOT2RST.current_figure
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References
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----------
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.. [1] Miguel Arevallilo Herraez, David R. Burton, Michael J. Lalor,
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and Munther A. Gdeisat, "Fast two-dimensional phase-unwrapping
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algorithm based on sorting by reliability following a noncontinuous
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path", Journal Applied Optics, Vol. 41, No. 35, pp. 7437, 2002
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"""
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