diff --git a/tests/test_rendertools.py b/tests/test_rendertools.py
index 39430d670297ac04c7fe9b01bb021889d612a7f0..b73b892a474180486d2a6d1d7143e6a5bee69e60 100644
--- a/tests/test_rendertools.py
+++ b/tests/test_rendertools.py
@@ -39,12 +39,12 @@ def checkFrozenImage(sFileImage):
     bytesFrozenImage = None
     for sDir in [ "/images/", "/images/test/" ]:
         sfPath = sDirRoot + sDir + sFileImage
-        with open(sfPath, "rb") as fIn:
-            bytesImage = fIn.read()
-            if bytesFrozenImage == None:
-                bytesFrozenImage = bytesImage
-            else:
-                assert(bytesFrozenImage == bytesImage)
+        bytesImage = plt.imread(sfPath)
+        if bytesFrozenImage is None:
+            bytesFrozenImage = bytesImage
+        else:
+            assert(bytesFrozenImage.shape == bytesImage.shape)
+            assert((np.sum(np.square(bytesFrozenImage-bytesImage)) / bytesFrozenImage.size) < 1e-3)
 
 
 def test_render_env():