Fix ColorHistogram to work with Open File

skimage/viewer/plugins/base.py

@@ -182,8 +182,13 @@ class Plugin(QtGui.QDialog):
         This method is called by the viewer when the original image is updated.
         """
         self.arguments[0] = image
+        self._on_new_image(image)
         self.filter_image()
 
+    def _on_new_image(self, image):
+        """Override this method to update your plugin for new images."""
+        pass
+
     @property
     def filtered_image(self):
         """Return filtered image."""

skimage/viewer/plugins/color_histogram.py

@@ -20,7 +20,10 @@ class ColorHistogram(PlotPlugin):
         super(ColorHistogram, self).attach(image_viewer)
 
         self.rect_tool = RectangleTool(self.ax, on_release=self.ab_selected)
-        self.lab_image = color.rgb2lab(image_viewer.image)
+        self._on_new_image(image_viewer.image)
+
+    def _on_new_image(self, image):
+        self.lab_image = color.rgb2lab(image)
 
         # Calculate color histogram in the Lab colorspace:
         L, a, b = self.lab_image.T

skimage/viewer/plugins/plotplugin.py

@@ -47,3 +47,7 @@ class PlotPlugin(Plugin):
             bgcolor = str(bgcolor / 255.)
         self.fig.patch.set_facecolor(bgcolor)
         self.layout.addWidget(self.canvas, self.row, 0)
+
+    def _update_original_image(self, image):
+        super(PlotPlugin, self)._update_original_image(image)
+        self.redraw()