ENH: Add rectangle tool and crop plugin example

skimage/viewer/plugins/crop.py

@@ -0,0 +1,34 @@
+from .base import Plugin
+from ..canvastools import RectangleTool
+from skimage.viewer.widgets.history import SaveButtons
+
+
+__all__ = ['Crop']
+
+
+class Crop(Plugin):
+    name = 'Crop'
+
+    def __init__(self, maxdist=10, **kwargs):
+        super(Crop, self).__init__(**kwargs)
+        self.maxdist = maxdist
+        self.add_widget(SaveButtons())
+        print self.help()
+
+    def attach(self, image_viewer):
+        super(Crop, self).attach(image_viewer)
+
+        self.rect_tool = RectangleTool(self.image_viewer.ax,
+                                       maxdist=self.maxdist,
+                                       on_enter=self.crop)
+
+    def help(self):
+        helpstr = ("Crop tool",
+                   "Select rectangular region and press enter to crop.")
+        return '\n'.join(helpstr)
+
+    def crop(self, extents):
+        xmin, xmax, ymin, ymax = extents
+        image = self.image_viewer.image[ymin:ymax+1, xmin:xmax+1]
+        self.image_viewer.image = image
+        self.image_viewer.ax.relim()