ENH: Add demo of LabelPlugin

viewer_examples/plugins/watershed_demo.py

@@ -0,0 +1,31 @@
+import matplotlib.pyplot as plt
+
+from skimage import data
+from skimage import filter
+from skimage import morphology
+from skimage.viewer import ImageViewer
+from skimage.viewer.plugins.labelplugin import LabelPainter
+
+
+class WatershedPlugin(LabelPainter):
+
+    def help(self):
+        helpstr = ("Watershed plugin",
+                   "----------------",
+                   "Use mouse to paint each region with a different label.",
+                   "Press enter to display segmented image.")
+        return '\n'.join(helpstr)
+
+    def on_enter(self, overlay):
+        viewer = self.image_viewer
+        edge_image = filter.sobel(viewer.image)
+        labels = morphology.watershed(edge_image, overlay)
+        viewer.ax.imshow(labels, cmap=plt.cm.jet, alpha=0.5)
+        viewer.redraw()
+        self.close()
+
+
+image = data.coins()
+viewer = ImageViewer(image)
+viewer += WatershedPlugin()
+viewer.show()