.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "auto_examples/cluster/plot_segmentation_toy.py" .. LINE NUMBERS ARE GIVEN BELOW. .. only:: html .. note:: :class: sphx-glr-download-link-note :ref:`Go to the end ` to download the full example code. or to run this example in your browser via Binder .. rst-class:: sphx-glr-example-title .. _sphx_glr_auto_examples_cluster_plot_segmentation_toy.py: =========================================== Spectral clustering for image segmentation =========================================== In this example, an image with connected circles is generated and spectral clustering is used to separate the circles. In these settings, the :ref:`spectral_clustering` approach solves the problem know as 'normalized graph cuts': the image is seen as a graph of connected voxels, and the spectral clustering algorithm amounts to choosing graph cuts defining regions while minimizing the ratio of the gradient along the cut, and the volume of the region. As the algorithm tries to balance the volume (ie balance the region sizes), if we take circles with different sizes, the segmentation fails. In addition, as there is no useful information in the intensity of the image, or its gradient, we choose to perform the spectral clustering on a graph that is only weakly informed by the gradient. This is close to performing a Voronoi partition of the graph. In addition, we use the mask of the objects to restrict the graph to the outline of the objects. In this example, we are interested in separating the objects one from the other, and not from the background. .. GENERATED FROM PYTHON SOURCE LINES 28-32 .. code-block:: Python # Authors: The scikit-learn developers # SPDX-License-Identifier: BSD-3-Clause .. GENERATED FROM PYTHON SOURCE LINES 33-35 Generate the data ----------------- .. GENERATED FROM PYTHON SOURCE LINES 35-52 .. code-block:: Python import numpy as np l = 100 x, y = np.indices((l, l)) center1 = (28, 24) center2 = (40, 50) center3 = (67, 58) center4 = (24, 70) radius1, radius2, radius3, radius4 = 16, 14, 15, 14 circle1 = (x - center1[0]) ** 2 + (y - center1[1]) ** 2 < radius1**2 circle2 = (x - center2[0]) ** 2 + (y - center2[1]) ** 2 < radius2**2 circle3 = (x - center3[0]) ** 2 + (y - center3[1]) ** 2 < radius3**2 circle4 = (x - center4[0]) ** 2 + (y - center4[1]) ** 2 < radius4**2 .. GENERATED FROM PYTHON SOURCE LINES 53-55 Plotting four circles --------------------- .. GENERATED FROM PYTHON SOURCE LINES 55-65 .. code-block:: Python img = circle1 + circle2 + circle3 + circle4 # We use a mask that limits to the foreground: the problem that we are # interested in here is not separating the objects from the background, # but separating them one from the other. mask = img.astype(bool) img = img.astype(float) img += 1 + 0.2 * np.random.randn(*img.shape) .. GENERATED FROM PYTHON SOURCE LINES 66-68 Convert the image into a graph with the value of the gradient on the edges. .. GENERATED FROM PYTHON SOURCE LINES 68-72 .. code-block:: Python from sklearn.feature_extraction import image graph = image.img_to_graph(img, mask=mask) .. GENERATED FROM PYTHON SOURCE LINES 73-75 Take a decreasing function of the gradient resulting in a segmentation that is close to a Voronoi partition .. GENERATED FROM PYTHON SOURCE LINES 75-77 .. code-block:: Python graph.data = np.exp(-graph.data / graph.data.std()) .. GENERATED FROM PYTHON SOURCE LINES 78-80 Here we perform spectral clustering using the arpack solver since amg is numerically unstable on this example. We then plot the results. .. GENERATED FROM PYTHON SOURCE LINES 80-94 .. code-block:: Python import matplotlib.pyplot as plt from sklearn.cluster import spectral_clustering labels = spectral_clustering(graph, n_clusters=4, eigen_solver="arpack") label_im = np.full(mask.shape, -1.0) label_im[mask] = labels fig, axs = plt.subplots(nrows=1, ncols=2, figsize=(10, 5)) axs[0].matshow(img) axs[1].matshow(label_im) plt.show() .. image-sg:: /auto_examples/cluster/images/sphx_glr_plot_segmentation_toy_001.png :alt: plot segmentation toy :srcset: /auto_examples/cluster/images/sphx_glr_plot_segmentation_toy_001.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 95-100 Plotting two circles -------------------- Here we repeat the above process but only consider the first two circles we generated. Note that this results in a cleaner separation between the circles as the region sizes are easier to balance in this case. .. GENERATED FROM PYTHON SOURCE LINES 100-119 .. code-block:: Python img = circle1 + circle2 mask = img.astype(bool) img = img.astype(float) img += 1 + 0.2 * np.random.randn(*img.shape) graph = image.img_to_graph(img, mask=mask) graph.data = np.exp(-graph.data / graph.data.std()) labels = spectral_clustering(graph, n_clusters=2, eigen_solver="arpack") label_im = np.full(mask.shape, -1.0) label_im[mask] = labels fig, axs = plt.subplots(nrows=1, ncols=2, figsize=(10, 5)) axs[0].matshow(img) axs[1].matshow(label_im) plt.show() .. image-sg:: /auto_examples/cluster/images/sphx_glr_plot_segmentation_toy_002.png :alt: plot segmentation toy :srcset: /auto_examples/cluster/images/sphx_glr_plot_segmentation_toy_002.png :class: sphx-glr-single-img .. rst-class:: sphx-glr-timing **Total running time of the script:** (0 minutes 0.605 seconds) .. _sphx_glr_download_auto_examples_cluster_plot_segmentation_toy.py: .. only:: html .. container:: sphx-glr-footer sphx-glr-footer-example .. container:: binder-badge .. image:: images/binder_badge_logo.svg :target: https://mybinder.org/v2/gh/scikit-learn/scikit-learn/main?urlpath=lab/tree/notebooks/auto_examples/cluster/plot_segmentation_toy.ipynb :alt: Launch binder :width: 150 px .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: plot_segmentation_toy.ipynb ` .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: plot_segmentation_toy.py ` .. container:: sphx-glr-download sphx-glr-download-zip :download:`Download zipped: plot_segmentation_toy.zip ` .. include:: plot_segmentation_toy.recommendations .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_