Use tf.nn.relu6 when appropriate in K.relu.

keras/backend/tensorflow_backend.py

@@ -3161,6 +3161,9 @@ def relu(x, alpha=0., max_value=None):
     # Returns
         A tensor.
     """
+    if alpha == 0 and max_value == 6:
+        return tf.nn.relu6(x)
+
     if alpha != 0.:
         x = tf.nn.leaky_relu(x, alpha)
     else:

tests/keras/activations_test.py

@@ -163,6 +163,19 @@ def test_relu():
     result = f([test_values])[0]
     assert_allclose(result, test_values, rtol=1e-05)
 
+    # Test max_value
+    test_values = [0.5, 1.5]
+    f = K.function([x], [activations.relu(x, max_value=1.)])
+    result = f([test_values])[0]
+    assert np.max(result) <= 1.
+
+    # Test max_value == 6.
+    test_values = [0.5, 6.]
+    f = K.function([x], [activations.relu(x, max_value=1.)])
+    result = f([test_values])[0]
+    assert np.max(result) <= 6.
+
+
 
 def test_elu():
     x = K.placeholder(ndim=2)