1.5.12.12. Demo connected components

Extracting and labeling connected components in a 2D array

import numpy as np
import matplotlib.pyplot as plt

Generate some binary data

x, y = np.indices((100, 100))
sig = (
    np.sin(2 * np.pi * x / 50.0)
    * np.sin(2 * np.pi * y / 50.0)
    * (1 + x * y / 50.0**2) ** 2
)
mask = sig > 1

plt.figure(figsize=(7, 3.5))
plt.subplot(1, 2, 1)
plt.imshow(sig)
plt.axis("off")
plt.title("sig")

plt.subplot(1, 2, 2)
plt.imshow(mask, cmap=plt.cm.gray)
plt.axis("off")
plt.title("mask")
plt.subplots_adjust(wspace=0.05, left=0.01, bottom=0.01, right=0.99, top=0.9)

Label connected components

import scipy as sp

labels, nb = sp.ndimage.label(mask)

plt.figure(figsize=(3.5, 3.5))
plt.imshow(labels)
plt.title("label")
plt.axis("off")

plt.subplots_adjust(wspace=0.05, left=0.01, bottom=0.01, right=0.99, top=0.9)

Extract the 4th connected component, and crop the array around it

sl = sp.ndimage.find_objects(labels == 4)
plt.figure(figsize=(3.5, 3.5))
plt.imshow(sig[sl[0]])
plt.title("Cropped connected component")
plt.axis("off")

plt.subplots_adjust(wspace=0.05, left=0.01, bottom=0.01, right=0.99, top=0.9)

plt.show()