ThresholdingΒΆ
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 (marked by a red line in the histogram below) by maximizing the variance between two classes of pixels, which are separated by the threshold. Equivalently, this 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=(8, 2.5))
plt.subplot(1, 3, 1)
plt.imshow(image, cmap=plt.cm.gray)
plt.title('Original')
plt.axis('off')
plt.subplot(1, 3, 2, aspect='equal')
plt.hist(image)
plt.title('Histogram')
plt.axvline(thresh, color='r')
plt.subplot(1, 3, 3)
plt.imshow(binary, cmap=plt.cm.gray)
plt.title('Thresholded')
plt.axis('off')
plt.show()
Python source code: download (generated using mpltools 0.6dev)