diff --git a/exp/color_sampler.py b/exp/color_sampler.py
--- a/exp/color_sampler.py
+++ b/exp/color_sampler.py
@@ -28,7 +28,8 @@ class Sampler:
 		self.letter="_"
 		self.hsv=(0,0,0)
 		self.pos=(0,0)
-		self.corners=Corners()
+		self.m=0
+		self._corners=[Corners()]
 		self._dirty=False
 
 		self._createGUI()
@@ -56,7 +57,9 @@ class Sampler:
 		self.canvas.create_image(0,0,image=self.photo,anchor="nw")
 		self.canvas.configure(width=w,height=h)
 
-		self.corners=Corners(self.annotations.get(self.filenames[self.k]) or [])
+		self.m=0
+		corners=self.annotations.get(self.filenames[self.k]) or []
+		self._corners=[Corners(c) for c in corners+[[]]]
 		self._markCorners()
 
 	def switchImage(self,step):
@@ -65,13 +68,18 @@ class Sampler:
 		self.k=(self.k+step+n)%n
 		self.showImage()
 
+	def switchCorners(self,step):
+		n=len(self._corners)
+		self.m=(self.m+step+n)%n
+		self._markCorners()
+
 	def setLetter(self,c):
 		self.letter=c
 		self.letterLabel.configure(text="Letter: {0}".format(c))
 
 	def addCorner(self,e):
 		self.corners.add(e.x,e.y)
-		self.annotations[self.filenames[self.k]]=list(self.corners)
+		self.annotations[self.filenames[self.k]]=[list(corns) for corns in self._corners if len(corns)>0]
 		self._dirty=True
 		self._markCorners()
 
@@ -98,6 +106,8 @@ class Sampler:
 		self.canvas.bind("<Motion>",self.sample)
 		root.bind("<Left>",lambda e: self.switchImage(-1))
 		root.bind("<Right>",lambda e: self.switchImage(1))
+		root.bind("<Up>",lambda e: self.switchCorners(-1))
+		root.bind("<Down>",lambda e: self.switchCorners(1))
 		root.bind("<b>",lambda e: self.setLetter("b"))
 		root.bind("<e>",lambda e: self.setLetter("e"))
 		root.bind("<w>",lambda e: self.setLetter("w"))
@@ -117,15 +127,21 @@ class Sampler:
 
 	def _markCorners(self):
 		self.canvas.delete("mark")
-		for c in self.corners:
-			(x,y)=(c.x,c.y)
-			self.canvas.create_oval(x-2,y-2,x+2,y+2,fill="#00ff00",tags="mark")
-		if self.corners.is_canon():
-			(a,b,c,d)=self.corners
-			self.canvas.create_line(a.x,a.y,b.x,b.y,fill="#00ff00",tags="mark")
-			self.canvas.create_line(b.x,b.y,c.x,c.y,fill="#00ff00",tags="mark")
-			self.canvas.create_line(c.x,c.y,d.x,d.y,fill="#00ff00",tags="mark")
-			self.canvas.create_line(d.x,d.y,a.x,a.y,fill="#00ff00",tags="mark")
+		for corns in self._corners:
+			for c in corns:
+				(x,y)=(c.x,c.y)
+				self.canvas.create_oval(x-2,y-2,x+2,y+2,fill="#00ff00",tags="mark")
+			if corns.is_canon():
+				(a,b,c,d)=corns
+				dash=tuple() if corns is self.corners else (4,4)
+				self.canvas.create_line(a.x,a.y,b.x,b.y,fill="#00ff00",dash=dash,tags="mark")
+				self.canvas.create_line(b.x,b.y,c.x,c.y,fill="#00ff00",dash=dash,tags="mark")
+				self.canvas.create_line(c.x,c.y,d.x,d.y,fill="#00ff00",dash=dash,tags="mark")
+				self.canvas.create_line(d.x,d.y,a.x,a.y,fill="#00ff00",dash=dash,tags="mark")
+
+	@property
+	def corners(self):
+		return self._corners[self.m]
 
 
 class DataFile(MutableMapping):