diff --git a/exp/color_sampler.py b/exp/color_sampler.py
--- a/exp/color_sampler.py
+++ b/exp/color_sampler.py
@@ -48,7 +48,9 @@ class Sampler:
 		print("\t".join(map(str, (self.filenames[self.k],*self.pos,self.letter,*self.hsv))))
 
 	def showImage(self):
-		self.img=Image.open(os.path.join(self.dirname,self.filenames[self.k]))
+		filename=self.filenames[self.k]
+		self.img=Image.open(os.path.join(self.dirname,filename))
+		self.root.title(filename)
 		(w,h)=self.img.size
 		self.photo=ImageTk.PhotoImage(self.img)
 		self.canvas.delete("all")
@@ -110,7 +112,7 @@ class Sampler:
 		self.annotations[self.filename]=[b for b in self._boards if not b.isEmpty()]
 
 	def _createGUI(self):
-		root=tk.Tk()
+		self.root=root=tk.Tk()
 		frame=tk.Frame(root)
 		frame.grid(column=0,row=0,sticky=(N,S,E,W))
 
diff --git a/exp/kerokero/prepare_data.py b/exp/kerokero/prepare_data.py
--- a/exp/kerokero/prepare_data.py
+++ b/exp/kerokero/prepare_data.py
@@ -2,7 +2,6 @@ import os
 import sys
 import re
 import random
-import itertools
 
 import numpy as np
 import cv2 as cv
@@ -40,7 +39,7 @@ class Sample:
 		img=cv.warpPerspective(self.img,m,(self.SIDE,self.SIDE))
 		img=np.float32(img)/128-1
 		grid=Corners(c.transform(m) for c in self.grid)
-		grid=list(map(lambda p: 2*p/self.SIDE-EPoint(1,1), grid))
+		grid=list(map(lambda p: list(2*p/self.SIDE-EPoint(1,1)), grid))
 		return (img,grid)
 
 	def _getCenter(self):