mirror of
https://github.com/wassname/scikit-image.git
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Johannes Schönberger
65 lines
1.5 KiB
Python
65 lines
1.5 KiB
Python
"""
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====================
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Local Otsu Threshold
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====================
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This example shows how Otsu's threshold [1]_ method can be applied locally. For
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each pixel, an "optimal" threshold is determined by maximizing the variance
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between two classes of pixels of the local neighborhood defined by a structuring
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element.
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The example compares the local threshold with the global threshold.
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.. note: local is much slower than global thresholding
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.. [1] http://en.wikipedia.org/wiki/Otsu's_method
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"""
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import matplotlib
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import matplotlib.pyplot as plt
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from skimage import data
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from skimage.morphology import disk
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from skimage.filter import threshold_otsu, rank
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from skimage.util import img_as_ubyte
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matplotlib.rcParams['font.size'] = 9
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img = img_as_ubyte(data.page())
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radius = 15
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selem = disk(radius)
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local_otsu = rank.otsu(img, selem)
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threshold_global_otsu = threshold_otsu(img)
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global_otsu = img >= threshold_global_otsu
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plt.figure(figsize=(8, 5))
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plt.subplot(2, 2, 1)
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plt.imshow(img, cmap=plt.cm.gray)
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plt.title('Original')
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plt.colorbar(orientation='horizontal')
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plt.axis('off')
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plt.subplot(2, 2, 2)
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plt.imshow(local_otsu, cmap=plt.cm.gray)
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plt.title('Local Otsu (radius=%d)' % radius)
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plt.colorbar(orientation='horizontal')
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plt.axis('off')
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plt.subplot(2, 2, 3)
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plt.imshow(img >= local_otsu, cmap=plt.cm.gray)
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plt.title('Original >= Local Otsu' % threshold_global_otsu)
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plt.axis('off')
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plt.subplot(2, 2, 4)
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plt.imshow(global_otsu, cmap=plt.cm.gray)
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plt.title('Global Otsu (threshold = %d)' % threshold_global_otsu)
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plt.axis('off')
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plt.show()
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