.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "auto_examples/applications/plot_coins_segmentation.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_applications_plot_coins_segmentation.py: ================================================== Comparing edge-based and region-based segmentation ================================================== In this example, we will see how to segment objects from a background. We use the ``coins`` image from ``skimage.data``, which shows several coins outlined against a darker background. .. GENERATED FROM PYTHON SOURCE LINES 10-26 .. code-block:: Python import numpy as np import matplotlib.pyplot as plt from skimage import data from skimage.exposure import histogram coins = data.coins() hist, hist_centers = histogram(coins) fig, axes = plt.subplots(1, 2, figsize=(8, 3)) axes[0].imshow(coins, cmap=plt.cm.gray) axes[0].set_axis_off() axes[1].plot(hist_centers, hist, lw=2) axes[1].set_title('histogram of gray values') .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_001.png :alt: histogram of gray values :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_001.png :class: sphx-glr-single-img .. rst-class:: sphx-glr-script-out .. code-block:: none Text(0.5, 1.0, 'histogram of gray values') .. GENERATED FROM PYTHON SOURCE LINES 27-34 Thresholding ============ A simple way to segment the coins is to choose a threshold based on the histogram of gray values. Unfortunately, thresholding this image gives a binary image that either misses significant parts of the coins or merges parts of the background with the coins: .. GENERATED FROM PYTHON SOURCE LINES 35-49 .. code-block:: Python fig, axes = plt.subplots(1, 2, figsize=(8, 3), sharey=True) axes[0].imshow(coins > 100, cmap=plt.cm.gray) axes[0].set_title('coins > 100') axes[1].imshow(coins > 150, cmap=plt.cm.gray) axes[1].set_title('coins > 150') for a in axes: a.set_axis_off() fig.tight_layout() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_002.png :alt: coins > 100, coins > 150 :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_002.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 50-56 Edge-based segmentation ======================= Next, we try to delineate the contours of the coins using edge-based segmentation. To do this, we first get the edges of features using the Canny edge-detector. .. GENERATED FROM PYTHON SOURCE LINES 56-66 .. code-block:: Python from skimage.feature import canny edges = canny(coins) fig, ax = plt.subplots(figsize=(4, 3)) ax.imshow(edges, cmap=plt.cm.gray) ax.set_title('Canny detector') ax.set_axis_off() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_003.png :alt: Canny detector :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_003.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 67-68 These contours are then filled using mathematical morphology. .. GENERATED FROM PYTHON SOURCE LINES 68-79 .. code-block:: Python from scipy import ndimage as ndi fill_coins = ndi.binary_fill_holes(edges) fig, ax = plt.subplots(figsize=(4, 3)) ax.imshow(fill_coins, cmap=plt.cm.gray) ax.set_title('filling the holes') ax.set_axis_off() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_004.png :alt: filling the holes :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_004.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 80-82 Small spurious objects are easily removed by setting a minimum size for valid objects. .. GENERATED FROM PYTHON SOURCE LINES 82-92 .. code-block:: Python from skimage import morphology coins_cleaned = morphology.remove_small_objects(fill_coins, 21) fig, ax = plt.subplots(figsize=(4, 3)) ax.imshow(coins_cleaned, cmap=plt.cm.gray) ax.set_title('removing small objects') ax.set_axis_off() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_005.png :alt: removing small objects :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_005.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 93-102 However, this method is not very robust, since contours that are not perfectly closed are not filled correctly, as is the case for one unfilled coin above. Region-based segmentation ========================= We therefore try a region-based method using the watershed transform. First, we find an elevation map using the Sobel gradient of the image. .. GENERATED FROM PYTHON SOURCE LINES 102-112 .. code-block:: Python from skimage.filters import sobel elevation_map = sobel(coins) fig, ax = plt.subplots(figsize=(4, 3)) ax.imshow(elevation_map, cmap=plt.cm.gray) ax.set_title('elevation map') ax.set_axis_off() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_006.png :alt: elevation map :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_006.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 113-115 Next we find markers of the background and the coins based on the extreme parts of the histogram of gray values. .. GENERATED FROM PYTHON SOURCE LINES 115-125 .. code-block:: Python markers = np.zeros_like(coins) markers[coins < 30] = 1 markers[coins > 150] = 2 fig, ax = plt.subplots(figsize=(4, 3)) ax.imshow(markers, cmap=plt.cm.nipy_spectral) ax.set_title('markers') ax.set_axis_off() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_007.png :alt: markers :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_007.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 126-128 Finally, we use the watershed transform to fill regions of the elevation map starting from the markers determined above: .. GENERATED FROM PYTHON SOURCE LINES 128-137 .. code-block:: Python from skimage import segmentation segmentation_coins = segmentation.watershed(elevation_map, markers) fig, ax = plt.subplots(figsize=(4, 3)) ax.imshow(segmentation_coins, cmap=plt.cm.gray) ax.set_title('segmentation') ax.set_axis_off() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_008.png :alt: segmentation :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_008.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 138-140 This last method works even better, and the coins can be segmented and labeled individually. .. GENERATED FROM PYTHON SOURCE LINES 140-158 .. code-block:: Python from skimage.color import label2rgb segmentation_coins = ndi.binary_fill_holes(segmentation_coins - 1) labeled_coins, _ = ndi.label(segmentation_coins) image_label_overlay = label2rgb(labeled_coins, image=coins, bg_label=0) fig, axes = plt.subplots(1, 2, figsize=(8, 3), sharey=True) axes[0].imshow(coins, cmap=plt.cm.gray) axes[0].contour(segmentation_coins, [0.5], linewidths=1.2, colors='y') axes[1].imshow(image_label_overlay) for a in axes: a.set_axis_off() fig.tight_layout() plt.show() .. image-sg:: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_009.png :alt: plot coins segmentation :srcset: /auto_examples/applications/images/sphx_glr_plot_coins_segmentation_009.png :class: sphx-glr-single-img .. rst-class:: sphx-glr-timing **Total running time of the script:** (0 minutes 1.535 seconds) .. _sphx_glr_download_auto_examples_applications_plot_coins_segmentation.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-image/scikit-image/v0.23.2?filepath=notebooks/auto_examples/applications/plot_coins_segmentation.ipynb :alt: Launch binder :width: 150 px .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: plot_coins_segmentation.ipynb ` .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: plot_coins_segmentation.py ` .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_