diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index 2d8c7175..50b7601c 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -1,9 +1,12 @@
 """
 Base class for Plugins that interact with ImageViewer.
 """
-from ..qt import QtGui
-from ..qt.QtCore import Qt
+from warnings import warn
 
+import numpy as np
+
+from ..qt import QtGui
+from ..qt.QtCore import Qt, Signal
 from ..utils import RequiredAttr, init_qtapp
 
 
@@ -71,14 +74,24 @@ class Plugin(QtGui.QDialog):
     name = 'Plugin'
     image_viewer = RequiredAttr("%s is not attached to ImageViewer" % name)
 
-    def __init__(self, image_filter=None, height=0, width=400, useblit=True):
+    # Signals used when viewers are linked to the Plugin output.
+    image_changed = Signal(np.ndarray)
+    _started = Signal(int)
+
+    def __init__(self, image_filter=None, height=0, width=400, useblit=True,
+                 dock='bottom'):
         init_qtapp()
         super(Plugin, self).__init__()
 
+        self.dock = dock
+
         self.image_viewer = None
         # If subclass defines `image_filter` method ignore input.
         if not hasattr(self, 'image_filter'):
             self.image_filter = image_filter
+        elif image_filter is not None:
+            warn("If the Plugin class defines an `image_filter` method, "
+                 "then the `image_filter` argument is ignored.")
 
         self.setWindowTitle(self.name)
         self.layout = QtGui.QGridLayout(self)
@@ -109,7 +122,7 @@ class Plugin(QtGui.QDialog):
         self.image_viewer = image_viewer
         self.image_viewer.plugins.append(self)
         #TODO: Always passing image as first argument may be bad assumption.
-        self.arguments.append(self.image_viewer.original_image)
+        self.arguments = [self.image_viewer.original_image]
 
         # Call filter so that filtered image matches widget values
         self.filter_image()
@@ -155,12 +168,22 @@ class Plugin(QtGui.QDialog):
         kwargs = dict([(name, self._get_value(a))
                        for name, a in self.keyword_arguments.items()])
         filtered = self.image_filter(*arguments, **kwargs)
+
         self.display_filtered_image(filtered)
+        self.image_changed.emit(filtered)
 
     def _get_value(self, param):
         # If param is a widget, return its `val` attribute.
         return param if not hasattr(param, 'val') else param.val
 
+    def _update_original_image(self, image):
+        """Update the original image argument passed to the filter function.
+
+        This method is called by the viewer when the original image is updated.
+        """
+        self.arguments[0] = image
+        self.filter_image()
+
     @property
     def filtered_image(self):
         """Return filtered image."""
@@ -183,6 +206,17 @@ class Plugin(QtGui.QDialog):
         """
         setattr(self, name, value)
 
+    def show(self, main_window=True):
+        """Show plugin."""
+        super(Plugin, self).show()
+        self.activateWindow()
+        self.raise_()
+
+        # Emit signal with x-hint so new windows can be displayed w/o overlap.
+        size = self.frameGeometry()
+        x_hint = size.x() + size.width()
+        self._started.emit(x_hint)
+
     def closeEvent(self, event):
         """On close disconnect all artists and events from ImageViewer.
 
diff --git a/skimage/viewer/plugins/color_histogram.py b/skimage/viewer/plugins/color_histogram.py
index 166b2805..39a75004 100644
--- a/skimage/viewer/plugins/color_histogram.py
+++ b/skimage/viewer/plugins/color_histogram.py
@@ -10,8 +10,9 @@ from ..canvastools import RectangleTool
 class ColorHistogram(PlotPlugin):
     name = 'Color Histogram'
 
-    def __init__(self, **kwargs):
+    def __init__(self, max_pct=0.99, **kwargs):
         super(ColorHistogram, self).__init__(height=400, **kwargs)
+        self.max_pct = max_pct
 
         print(self.help())
 
@@ -30,7 +31,7 @@ class ColorHistogram(PlotPlugin):
                                                 normed=True)
 
         # Clip bin heights that dominate a-b histogram
-        max_val = pct_total_area(hist, percentile=99)
+        max_val = pct_total_area(hist, percentile=self.max_pct)
         hist = exposure.rescale_intensity(hist, in_range=(0, max_val))
         self.ax.imshow(hist, extent=ab_extents, cmap=plt.cm.gray)
 
@@ -55,12 +56,12 @@ class ColorHistogram(PlotPlugin):
         self.image_viewer.image = color.lab2rgb(lab_masked)
 
 
-def pct_total_area(image, percentile=80):
+def pct_total_area(image, percentile=0.80):
     """Return threshold value based on percentage of total area.
 
     The specified percent of pixels less than the given intensity threshold.
     """
-    idx = int((image.size - 1) * percentile / 100.0)
+    idx = int((image.size - 1) * percentile)
     sorted_pixels = np.sort(image.flat)
     return sorted_pixels[idx]
 
diff --git a/skimage/viewer/plugins/overlayplugin.py b/skimage/viewer/plugins/overlayplugin.py
index 278f072c..25ea3b00 100644
--- a/skimage/viewer/plugins/overlayplugin.py
+++ b/skimage/viewer/plugins/overlayplugin.py
@@ -2,7 +2,7 @@ from warnings import warn
 
 from skimage.util.dtype import dtype_range
 from .base import Plugin
-from ..utils import ClearColormap
+from ..utils import ClearColormap, update_axes_image
 
 
 __all__ = ['OverlayPlugin']
@@ -66,7 +66,8 @@ class OverlayPlugin(Plugin):
             self._overlay_plot = ax.imshow(image, cmap=self.cmap,
                                            vmin=vmin, vmax=vmax)
         else:
-            self._overlay_plot.set_array(image)
+            update_axes_image(self._overlay_plot, image)
+
         self.image_viewer.redraw()
 
     @property
diff --git a/skimage/viewer/plugins/plotplugin.py b/skimage/viewer/plugins/plotplugin.py
index c120756c..0ce5df73 100644
--- a/skimage/viewer/plugins/plotplugin.py
+++ b/skimage/viewer/plugins/plotplugin.py
@@ -17,6 +17,13 @@ class PlotPlugin(Plugin):
     See base Plugin class for additional details.
     """
 
+    def __init__(self, image_filter=None, height=150, width=400, **kwargs):
+        super(PlotPlugin, self).__init__(image_filter=image_filter,
+                                         height=height, width=width, **kwargs)
+
+        self._height = height
+        self._width = width
+
     def attach(self, image_viewer):
         super(PlotPlugin, self).attach(image_viewer)
         # Add plot for displaying intensity profile.
@@ -26,10 +33,12 @@ class PlotPlugin(Plugin):
         """Redraw plot."""
         self.canvas.draw_idle()
 
-    def add_plot(self, height=4, width=4):
-        self.fig, self.ax = new_plot(figsize=(height, width))
+    def add_plot(self):
+        self.fig, self.ax = new_plot()
+        self.fig.set_figwidth(self._width / float(self.fig.dpi))
+        self.fig.set_figheight(self._height / float(self.fig.dpi))
+
         self.canvas = self.fig.canvas
-        self.canvas.setMinimumHeight(150)
         #TODO: Converted color is slightly different than Qt background.
         qpalette = QtGui.QPalette()
         qcolor = qpalette.color(QtGui.QPalette.Window)
diff --git a/skimage/viewer/qt/QtCore.py b/skimage/viewer/qt/QtCore.py
index 897b8760..19b92a53 100644
--- a/skimage/viewer/qt/QtCore.py
+++ b/skimage/viewer/qt/QtCore.py
@@ -4,6 +4,19 @@ if qt_api == 'pyside':
     from PySide.QtCore import *
 elif qt_api == 'pyqt':
     from PyQt4.QtCore import *
+    # Use pyside names for signals and slots
+    Signal = pyqtSignal
+    Slot = pyqtSlot
 else:
-    # Mock objects
-    Qt = None
+    # Mock objects for buildbot (which doesn't have Qt, but imports viewer).
+    class Qt(object):
+        TopDockWidgetArea = None
+        BottomDockWidgetArea = None
+        LeftDockWidgetArea = None
+        RightDockWidgetArea = None
+
+    def Signal(*args, **kwargs):
+        pass
+
+    def Slot(*args, **kwargs):
+        pass
diff --git a/skimage/viewer/utils/core.py b/skimage/viewer/utils/core.py
index e4985a9e..3b9b33fb 100644
--- a/skimage/viewer/utils/core.py
+++ b/skimage/viewer/utils/core.py
@@ -23,7 +23,8 @@ from ..qt import QtGui
 
 
 __all__ = ['init_qtapp', 'start_qtapp', 'RequiredAttr', 'figimage',
-           'LinearColormap', 'ClearColormap', 'FigureCanvas', 'new_plot']
+           'LinearColormap', 'ClearColormap', 'FigureCanvas', 'new_plot',
+           'update_axes_image']
 
 
 QApp = None
@@ -35,29 +36,53 @@ def init_qtapp():
     The QApplication needs to be initialized before creating any QWidgets
     """
     global QApp
+    QApp = QtGui.QApplication.instance()
     if QApp is None:
         QApp = QtGui.QApplication([])
+    return QApp
 
 
-def start_qtapp():
+def is_event_loop_running(app=None):
+    """Return True if event loop is running."""
+    if app is None:
+        app = init_qtapp()
+    if hasattr(app, '_in_event_loop'):
+        return app._in_event_loop
+    else:
+        return False
+
+
+def start_qtapp(app=None):
     """Start Qt mainloop"""
-    QApp.exec_()
+    if app is None:
+        app = init_qtapp()
+    if not is_event_loop_running(app):
+        app._in_event_loop = True
+        app.exec_()
+        app._in_event_loop = False
+    else:
+        app._in_event_loop = True
 
 
 class RequiredAttr(object):
     """A class attribute that must be set before use."""
 
-    def __init__(self, msg):
+    instances = dict()
+
+    def __init__(self, msg='Required attribute not set', init_val=None):
+        self.instances[self, None] = init_val
         self.msg = msg
-        self.val = None
 
     def __get__(self, obj, objtype):
-        if self.val is None:
+        value = self.instances[self, obj]
+        if value is None:
+            # Should raise an error but that causes issues with the buildbot.
             warnings.warn(self.msg)
-        return self.val
+            self.__set__(obj, self.init_val)
+        return value
 
-    def __set__(self, obj, val):
-        self.val = val
+    def __set__(self, obj, value):
+        self.instances[self, obj] = value
 
 
 class LinearColormap(LinearSegmentedColormap):
@@ -179,3 +204,22 @@ def figimage(image, scale=1, dpi=None, **kwargs):
     ax.set_axis_off()
     ax.imshow(image, **kwargs)
     return fig, ax
+
+
+def update_axes_image(image_axes, image):
+    """Update the image displayed by an image plot.
+
+    This sets the image plot's array and updates its shape appropriately
+
+    Parameters
+    ----------
+    image_axes : `matplotlib.image.AxesImage`
+        Image axes to update.
+    image : array
+        Image array.
+    """
+    image_axes.set_array(image)
+
+    # Adjust size if new image shape doesn't match the original
+    h, w = image.shape[:2]
+    image_axes.set_extent((0, w, h, 0))
diff --git a/skimage/viewer/viewers/core.py b/skimage/viewer/viewers/core.py
index 9d6261c6..c3ffeb1e 100644
--- a/skimage/viewer/viewers/core.py
+++ b/skimage/viewer/viewers/core.py
@@ -2,7 +2,7 @@
 ImageViewer class for viewing and interacting with images.
 """
 from ..qt import QtGui
-from ..qt import QtCore
+from ..qt.QtCore import Qt, Signal
 
 from skimage import io, img_as_float
 from skimage.util.dtype import dtype_range
@@ -11,6 +11,7 @@ import numpy as np
 from .. import utils
 from ..widgets import Slider
 from ..utils import dialogs
+from ..plugins.base import Plugin
 
 
 __all__ = ['ImageViewer', 'CollectionViewer']
@@ -59,6 +60,15 @@ class ImageViewer(QtGui.QMainWindow):
     >>> # viewer.show()
 
     """
+
+    dock_areas = {'top': Qt.TopDockWidgetArea,
+                  'bottom': Qt.BottomDockWidgetArea,
+                  'left': Qt.LeftDockWidgetArea,
+                  'right': Qt.RightDockWidgetArea}
+
+    # Signal that the original image has been changed
+    original_image_changed = Signal(np.ndarray)
+
     def __init__(self, image):
         # Start main loop
         utils.init_qtapp()
@@ -66,21 +76,28 @@ class ImageViewer(QtGui.QMainWindow):
 
         #TODO: Add ImageViewer to skimage.io window manager
 
-        self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
+        self.setAttribute(Qt.WA_DeleteOnClose)
         self.setWindowTitle("Image Viewer")
 
         self.file_menu = QtGui.QMenu('&File', self)
         self.file_menu.addAction('Open file', self.open_file,
-                                 QtCore.Qt.CTRL + QtCore.Qt.Key_O)
+                                 Qt.CTRL + Qt.Key_O)
         self.file_menu.addAction('Save to file', self.save_to_file,
-                                 QtCore.Qt.CTRL + QtCore.Qt.Key_S)
+                                 Qt.CTRL + Qt.Key_S)
         self.file_menu.addAction('Quit', self.close,
-                                 QtCore.Qt.CTRL + QtCore.Qt.Key_Q)
+                                 Qt.CTRL + Qt.Key_Q)
         self.menuBar().addMenu(self.file_menu)
 
         self.main_widget = QtGui.QWidget()
         self.setCentralWidget(self.main_widget)
 
+        if isinstance(image, Plugin):
+            plugin = image
+            image = plugin.filtered_image
+            plugin.image_changed.connect(self._update_original_image)
+            # When plugin is started, start
+            plugin._started.connect(self._show)
+
         self.fig, self.ax = utils.figimage(image)
         self.canvas = self.fig.canvas
         self.canvas.setParent(self)
@@ -88,9 +105,7 @@ class ImageViewer(QtGui.QMainWindow):
         self.ax.autoscale(enable=False)
 
         self._image_plot = self.ax.images[0]
-
-        self.original_image = image
-        self.image = image.copy()
+        self._update_original_image(image)
         self.plugins = []
 
         self.layout = QtGui.QVBoxLayout(self.main_widget)
@@ -107,16 +122,48 @@ class ImageViewer(QtGui.QMainWindow):
     def __add__(self, plugin):
         """Add plugin to ImageViewer"""
         plugin.attach(self)
+        self.original_image_changed.connect(plugin._update_original_image)
+
+        if plugin.dock:
+            location = self.dock_areas[plugin.dock]
+            dock_location = Qt.DockWidgetArea(location)
+            dock = QtGui.QDockWidget()
+            dock.setWidget(plugin)
+            dock.setWindowTitle(plugin.name)
+            self.addDockWidget(dock_location, dock)
+
+            horiz = (self.dock_areas['left'], self.dock_areas['right'])
+            dimension = 'width' if location in horiz else 'height'
+            self._add_widget_size(plugin, dimension=dimension)
+
         return self
 
+    def _add_widget_size(self, widget, dimension='width'):
+        widget_size = widget.sizeHint()
+        viewer_size = self.frameGeometry()
+
+        dx = dy = 0
+        if dimension == 'width':
+            dx = widget_size.width()
+        elif dimension == 'height':
+            dy = widget_size.height()
+
+        w = viewer_size.width()
+        h = viewer_size.height()
+        self.resize(w + dx, h + dy)
+
     def open_file(self):
         """Open image file and display in viewer."""
         filename = dialogs.open_file_dialog()
         if filename is None:
             return
         image = io.imread(filename)
+        self._update_original_image(image)
+
+    def _update_original_image(self, image):
         self.original_image = image     # update saved image
-        self.image = image              # update displayed image
+        self.image = image.copy()       # update displayed image
+        self.original_image_changed.emit(image)
 
     def save_to_file(self):
         """Save current image to file.
@@ -149,27 +196,22 @@ class ImageViewer(QtGui.QMainWindow):
     def closeEvent(self, event):
         self.close()
 
-    def auto_layout(self):
-        """Move viewer to top-left and align plugin on right edge of viewer."""
-        size = self.geometry()
-        self.move(0, 0)
-        w = size.width()
-        y = 0
-        #TODO: Layout isn't quite correct for multiple plugins (overlaps).
+    def _show(self, x=0):
+        self.move(x, 0)
         for p in self.plugins:
-            p.move(w, y)
-            y += p.geometry().height()
+            p.show()
+        super(ImageViewer, self).show()
+        self.activateWindow()
+        self.raise_()
 
-    def show(self):
+    def show(self, main_window=True):
         """Show ImageViewer and attached plugins.
 
         This behaves much like `matplotlib.pyplot.show` and `QWidget.show`.
         """
-        self.auto_layout()
-        for p in self.plugins:
-            p.show()
-        super(ImageViewer, self).show()
-        utils.start_qtapp()
+        self._show()
+        if main_window:
+            utils.start_qtapp()
 
     def redraw(self):
         self.canvas.draw_idle()
@@ -181,13 +223,10 @@ class ImageViewer(QtGui.QMainWindow):
     @image.setter
     def image(self, image):
         self._img = image
-        self._image_plot.set_array(image)
+        utils.update_axes_image(self._image_plot, image)
 
-        # Adjust size if new image shape doesn't match the original
-        h, w = image.shape[:2]
-        # update data coordinates (otherwise pixel coordinates are off)
-        self._image_plot.set_extent((0, w, h, 0))
         # update display (otherwise image doesn't fill the canvas)
+        h, w = image.shape[:2]
         self.ax.set_xlim(0, w)
         self.ax.set_ylim(h, 0)
 
@@ -248,7 +287,7 @@ class CollectionViewer(ImageViewer):
     ----------
     image_collection : list of images
         List of images to be displayed.
-    update_on : {'on_slide' | 'on_release'}
+    update_on : {'move' | 'release'}
         Control whether image is updated on slide or release of the image
         slider. Using 'on_release' will give smoother behavior when displaying
         large images or when writing a plugin/subclass that requires heavy
@@ -296,7 +335,7 @@ class CollectionViewer(ImageViewer):
         This method can be overridden or extended in subclasses and plugins to
         react to image changes.
         """
-        self.image = image
+        self._update_original_image(image)
 
     def keyPressEvent(self, event):
         if type(event) == QtGui.QKeyEvent:
diff --git a/skimage/viewer/widgets/core.py b/skimage/viewer/widgets/core.py
index ad69bfcf..b9714d38 100644
--- a/skimage/viewer/widgets/core.py
+++ b/skimage/viewer/widgets/core.py
@@ -81,7 +81,7 @@ class Slider(BaseWidget):
         Range of slider values.
     value : float
         Default slider value. If None, use midpoint between `low` and `high`.
-    value : {'float' | 'int'}
+    value_type : {'float' | 'int'}
         Numeric type of slider value.
     ptype : {'arg' | 'kwarg' | 'plugin'}
         Parameter type.
@@ -90,12 +90,12 @@ class Slider(BaseWidget):
         is typically set when the widget is added to a plugin.
     orientation : {'horizontal' | 'vertical'}
         Slider orientation.
-    update_on : {'move' | 'release'}
+    update_on : {'release' | 'move'}
         Control when callback function is called: on slider move or release.
     """
     def __init__(self, name, low=0.0, high=1.0, value=None, value_type='float',
                  ptype='kwarg', callback=None, max_edit_width=60,
-                 orientation='horizontal', update_on='move'):
+                 orientation='horizontal', update_on='release'):
         super(Slider, self).__init__(name, ptype, callback)
 
         if value is None:
diff --git a/viewer_examples/plugins/canny_simple.py b/viewer_examples/plugins/canny_simple.py
index 912401e1..c26ca08d 100644
--- a/viewer_examples/plugins/canny_simple.py
+++ b/viewer_examples/plugins/canny_simple.py
@@ -12,9 +12,9 @@ image = data.camera()
 # You can create a UI for a filter just by passing a filter function...
 plugin = OverlayPlugin(image_filter=canny)
 # ... and adding widgets to adjust parameter values.
-plugin += Slider('sigma', 0, 5, update_on='release')
-plugin += Slider('low threshold', 0, 255, update_on='release')
-plugin += Slider('high threshold', 0, 255, update_on='release')
+plugin += Slider('sigma', 0, 5)
+plugin += Slider('low threshold', 0, 255)
+plugin += Slider('high threshold', 0, 255)
 # ... and we can also add buttons to save the overlay:
 plugin += SaveButtons(name='Save overlay to:')
 
diff --git a/viewer_examples/plugins/collection_overlay.py b/viewer_examples/plugins/collection_overlay.py
new file mode 100644
index 00000000..4c7002f2
--- /dev/null
+++ b/viewer_examples/plugins/collection_overlay.py
@@ -0,0 +1,21 @@
+"""
+==============================================
+``CollectionViewer`` with an ``OverlayPlugin``
+==============================================
+
+Demo of a CollectionViewer for viewing collections of images with an
+overlay plugin.
+
+"""
+from skimage import data
+
+from skimage.viewer import CollectionViewer
+from skimage.viewer.plugins.canny import CannyPlugin
+
+
+img_collection = [data.camera(), data.coins(), data.text()]
+
+viewer = CollectionViewer(img_collection)
+viewer += CannyPlugin()
+
+viewer.show()
diff --git a/viewer_examples/plugins/collection_plugin.py b/viewer_examples/plugins/collection_plugin.py
new file mode 100644
index 00000000..65ff1f21
--- /dev/null
+++ b/viewer_examples/plugins/collection_plugin.py
@@ -0,0 +1,33 @@
+"""
+==================================
+``CollectionViewer`` with a 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')
+plugin.name = "Autolevel"
+
+viewer = CollectionViewer(img_collection)
+viewer += plugin
+
+viewer.show()
diff --git a/viewer_examples/plugins/color_histogram.py b/viewer_examples/plugins/color_histogram.py
index 0b654b3e..6b091d69 100644
--- a/viewer_examples/plugins/color_histogram.py
+++ b/viewer_examples/plugins/color_histogram.py
@@ -5,5 +5,5 @@ from skimage import data
 
 image = data.load('color.png')
 viewer = ImageViewer(image)
-viewer += ColorHistogram()
+viewer += ColorHistogram(dock='right')
 viewer.show()
diff --git a/viewer_examples/plugins/median_filter.py b/viewer_examples/plugins/median_filter.py
index a20ad8f3..36593c3d 100644
--- a/viewer_examples/plugins/median_filter.py
+++ b/viewer_examples/plugins/median_filter.py
@@ -10,7 +10,7 @@ image = data.coins()
 viewer = ImageViewer(image)
 
 plugin = Plugin(image_filter=median_filter)
-plugin += Slider('radius', 2, 10, value_type='int', update_on='release')
+plugin += Slider('radius', 2, 10, value_type='int')
 plugin += SaveButtons()
 plugin += OKCancelButtons()
 
diff --git a/viewer_examples/plugins/probabilistic_hough.py b/viewer_examples/plugins/probabilistic_hough.py
new file mode 100644
index 00000000..98052f87
--- /dev/null
+++ b/viewer_examples/plugins/probabilistic_hough.py
@@ -0,0 +1,46 @@
+import numpy as np
+
+from skimage import data
+from skimage import draw
+from skimage.transform import probabilistic_hough_line
+
+from skimage.viewer import ImageViewer
+from skimage.viewer.widgets import Slider
+from skimage.viewer.plugins.overlayplugin import OverlayPlugin
+from skimage.viewer.plugins.canny import CannyPlugin
+
+
+def line_image(shape, lines):
+    image = np.zeros(shape, dtype=bool)
+    for end_points in lines:
+        # hough lines returns (x, y) points, draw.line wants (row, columns)
+        end_points = np.asarray(end_points)[:, ::-1]
+        image[draw.line(*np.ravel(end_points))] = 1
+    return image
+
+
+def hough_lines(image, *args, **kwargs):
+    # Set threshold to 0.5 since we're working with a binary image (from canny)
+    lines = probabilistic_hough_line(image, threshold=0.5, *args, **kwargs)
+    image = line_image(image.shape, lines)
+    return image
+
+
+image = data.camera()
+canny_viewer = ImageViewer(image)
+canny_plugin = CannyPlugin()
+canny_viewer += canny_plugin
+
+hough_plugin = OverlayPlugin(image_filter=hough_lines)
+hough_plugin.name = 'Hough Lines'
+
+hough_plugin += Slider('line length', 0, 100)
+hough_plugin += Slider('line gap', 0, 20)
+
+# Passing a plugin to a viewer connects the output of the plugin to the viewer.
+hough_viewer = ImageViewer(canny_plugin)
+hough_viewer += hough_plugin
+
+# Show viewers displays both viewers since `hough_viewer` is connected to
+# `canny_viewer` through `canny_plugin`
+canny_viewer.show()