move CollectionViewer update_image to parent class

skimage/viewer/viewers/core.py

@@ -153,6 +153,9 @@ class ImageViewer(QtWidgets.QMainWindow):
     for showing images. `ImageViewer` doesn't subclass the Matplotlib axes (or
     figure) because of the high probability of name collisions.
 
+    Subclasses and plugins will likely extend the `update_image` method to add
+    custom overlays or filter the displayed image.
+
     Parameters
     ----------
     image : array
@@ -283,6 +286,14 @@ class ImageViewer(QtWidgets.QMainWindow):
         image = io.imread(filename)
         self._update_original_image(image)
 
+    def update_image(self, image):
+        """Update displayed image.
+
+        This method can be overridden or extended in subclasses and plugins to
+        react to image changes.
+        """
+        self._update_original_image(image)
+
     def _update_original_image(self, image):
         self.original_image = image     # update saved image
         self.image = image.copy()       # update displayed image
@@ -423,9 +434,6 @@ class CollectionViewer(ImageViewer):
         home/end keys
             First/last image in collection.
 
-    Subclasses and plugins will likely extend the `update_image` method to add
-    custom overlays or filter the displayed image.
-
     Parameters
     ----------
     image_collection : list of images
@@ -472,14 +480,6 @@ class CollectionViewer(ImageViewer):
         self.slider.val = index
         self.update_image(self.image_collection[index])
 
-    def update_image(self, image):
-        """Update displayed image.
-
-        This method can be overridden or extended in subclasses and plugins to
-        react to image changes.
-        """
-        self._update_original_image(image)
-
     def keyPressEvent(self, event):
         if type(event) == QtWidgets.QKeyEvent:
             key = event.key()