diff --git a/skimage/io/_plugins/q_color_mixer.py b/skimage/io/_plugins/q_color_mixer.py
index 085bd751..7a5d1778 100644
--- a/skimage/io/_plugins/q_color_mixer.py
+++ b/skimage/io/_plugins/q_color_mixer.py
@@ -6,7 +6,6 @@ from PyQt4.QtCore import Qt
 from util import ColorMixer
 
 
-
 class IntelligentSlider(QWidget):
     ''' A slider that adds a 'name' attribute and calls a callback
     with 'name' as an argument to the registered callback.
@@ -19,7 +18,8 @@ class IntelligentSlider(QWidget):
     The range of the slider is hardcoded from zero - 1000,
     but it supports a conversion factor so you can scale the results'''
 
-    def __init__(self, name, a, b, callback, orientation='vertical'):
+    def __init__(self, name, a, b, callback, orientation='vertical',
+                 update_on='move'):
         QWidget.__init__(self)
         self.name = name
         self.callback = callback
@@ -41,7 +41,12 @@ class IntelligentSlider(QWidget):
         self.slider = QSlider(orientation_slider)
         self.slider.setRange(0, 1000)
         self.slider.setValue(500)
-        self.slider.valueChanged.connect(self.slider_changed)
+        if update_on == 'move':
+            self.slider.sliderMoved.connect(self.slider_changed)
+        elif update_on == 'release':
+            self.slider.sliderReleased.connect(self.slider_changed)
+        else:
+            raise ValueError("Unexpected value %s for 'update_on'" % update_on)
 
         self.name_label = QLabel()
         self.name_label.setText(self.name)
@@ -62,9 +67,12 @@ class IntelligentSlider(QWidget):
             self.layout.addWidget(self.name_label, 0, 0)
             self.layout.addWidget(self.slider, 0, 1, alignment)
             self.layout.addWidget(self.value_label, 0, 2)
+        else:
+            msg = "Unexpected value %s for 'orientation'"
+            raise ValueError(msg % orientation)
 
     # bind this to the valueChanged signal of the slider
-    def slider_changed(self, val):
+    def slider_changed(self):
         val = self.val()
         self.value_label.setText(str(val)[:4])
 
diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index aa7229ad..1757f257 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -98,17 +98,17 @@ class Plugin(QtGui.QDialog):
         else:
             return param
 
-    def add_argument(self, name, low, high, callback):
-        name, slider = self.add_slider(name, low, high, callback)
+    def add_argument(self, name, low, high, callback, **kwargs):
+        name, slider = self.add_slider(name, low, high, callback, **kwargs)
         self.arguments[name] = slider
 
-    def add_keyword_argument(self, name, low, high, callback):
-        name, slider = self.add_slider(name, low, high, callback)
+    def add_keyword_argument(self, name, low, high, callback, **kwargs):
+        name, slider = self.add_slider(name, low, high, callback, **kwargs)
         self.keyword_arguments[name] = slider
 
-    def add_slider(self, name, low, high, callback):
+    def add_slider(self, name, low, high, callback, **kwargs):
         slider = IntelligentSlider(name, low, high, callback,
-                                   orientation='horizontal')
+                                   orientation='horizontal', **kwargs)
         self.layout.addWidget(slider, self.row, 0)
         self.row += 1
         return name.replace(' ', '_'), slider
diff --git a/skimage/viewer/plugins/canny.py b/skimage/viewer/plugins/canny.py
index 88312036..cf3b5253 100644
--- a/skimage/viewer/plugins/canny.py
+++ b/skimage/viewer/plugins/canny.py
@@ -11,9 +11,12 @@ class CannyPlugin(Plugin):
         width = kwargs.get('width', 400)
         super(CannyPlugin, self).__init__(image_viewer,
                                           width=width, height=height)
-        self.add_keyword_argument('sigma', 0.005, 0, self.caller)
-        self.add_keyword_argument('low_threshold', 0.255, 0, self.caller)
-        self.add_keyword_argument('high_threshold', 0.255, 0, self.caller)
+        self.add_keyword_argument('sigma', 0.005, 0, self.caller,
+                                  update_on='release')
+        self.add_keyword_argument('low_threshold', 0.255, 0, self.caller,
+                                  update_on='release')
+        self.add_keyword_argument('high_threshold', 0.255, 0, self.caller,
+                                  update_on='release')
         # Call callback so that image is updated to slider values.
         self.caller()