diff --git a/exp/board_detect.py b/exp/board_detect.py
--- a/exp/board_detect.py
+++ b/exp/board_detect.py
@@ -105,7 +105,11 @@ class BoardDetector:
 		# quantize colors
 		colors=self._sampleColors(rect)
 		quantized=quantize(rect,colors)
-		show(quantized,filename)
+		gray=cv.cvtColor(rect,cv.COLOR_BGR2GRAY)
+		edges=cv.Canny(gray,70,130)
+		show(edges,"edges")
+		quantized=quantized & (255-cv.cvtColor(edges,cv.COLOR_GRAY2BGR))
+		show(quantized,"quantized, edges separated")
 
 		# detect black and white stones
 		stones=self._detectStones(quantized,colors)
@@ -165,16 +169,16 @@ class BoardDetector:
 
 	def _maskStones(self,quantized,colors):
 		unit=np.array([1,1,1],dtype=np.uint8)
-		kernel=np.ones((3,3),np.uint8)
 		maskB=cv.inRange(quantized,colors[0]-unit,colors[0]+unit)
-		maskB=cv.morphologyEx(maskB,cv.MORPH_OPEN,kernel,iterations=1)
-		maskB=cv.erode(maskB,kernel,iterations=3)
-		# distTransform = cv.distanceTransform(maskB,cv.DIST_L2,5)
-		# maskB=cv.inRange(distTransform,6,10)
+
+		distTransform=cv.distanceTransform(maskB,cv.DIST_L2,5)
+		maskB=cv.inRange(distTransform,6,20)
 		show(maskB,"black areas")
+
 		maskW=cv.inRange(quantized,colors[1]-unit,colors[1]+unit)
-		maskW=cv.morphologyEx(maskW,cv.MORPH_OPEN,kernel,iterations=1)
-		maskW=cv.erode(maskW,kernel,iterations=2)
+		distTransform=cv.distanceTransform(maskW,cv.DIST_L2,5)
+		maskW=cv.inRange(distTransform,6,20)
+
 		show(maskW,"white areas")
 		stones=cv.bitwise_or(maskB,maskW)
 		show(stones,"black and white areas")