Add example of connecting plugins to CollectionViewer

viewer_examples/plugins/collection_plugin.py

@@ -0,0 +1,33 @@
+"""
+=================
+Collection plugin
+=================
+
+Demo of a CollectionViewer for viewing collections of images with the
+`autolevel` rank filter connected as a plugin.
+
+"""
+from skimage import data
+from skimage.filter import rank
+from skimage.morphology import disk
+
+from skimage.viewer import CollectionViewer
+from skimage.viewer.widgets import Slider
+from skimage.viewer.plugins.base import Plugin
+
+
+# Wrap autolevel function to make the disk size a filter argument.
+def autolevel(image, disk_size):
+    return rank.autolevel(image, disk(disk_size))
+
+
+img_collection = [data.camera(), data.coins(), data.text()]
+
+plugin = Plugin(image_filter=autolevel)
+plugin += Slider('disk_size', 2, 8, value_type='int', update_on='release')
+plugin.name = "Autolevel"
+
+viewer = CollectionViewer(img_collection)
+viewer += plugin
+
+viewer.show()