"""
============
Thresholding
============

Thresholding is used to create a binary image. This example uses Otsu's method
to calculate the threshold value.

Otsu's method calculates an "optimal" threshold by maximizing the variance
between the two classes of pixels, which are separated by the threshold.
Equivalently, the optimal threshold minimizes the intra-class variance.

.. [1] http://en.wikipedia.org/wiki/Otsu's_method

"""

import matplotlib.pyplot as plt

from skimage.data import camera
from skimage.filter import threshold_otsu


image = camera()
thresh = threshold_otsu(image)
binary = image > thresh

plt.figure(figsize=(10, 3.5))
plt.subplot(1, 3, 1)
plt.imshow(image)
plt.title('original')
plt.axis('off')

plt.subplot(1, 3, 2)
plt.hist(image)
plt.title('histogram')
plt.axvline(thresh, color='r')

plt.subplot(1, 3, 3)
plt.imshow(binary)
plt.title('thresholded')
plt.axis('off')

plt.show()