title: Why my loss function or accuracy does not improve?
body: <p>I have 3D CNN U-net architecture to solve segmentation problem. I am using Adam optimisation together with binary cross entropy and the metric is "accuracy". I try to understand why it does not improve.  </p>
  
  <pre><code>Train on 2774 samples, validate on 694 samples
  Epoch 1/20
  2774/2774 [==============================] - 166s 60ms/step - loss: 0.5189 - acc: 0.7928 - val_loss: 0.5456 - val_acc: 0.7674
  
  Epoch 00001: val_loss improved from inf to 0.54555, saving model to model-tgs-salt-1.h5
  Epoch 2/20
  2774/2774 [==============================] - 170s 61ms/step - loss: 0.5170 - acc: 0.7928 - val_loss: 0.5485 - val_acc: 0.7674
  
  Epoch 00002: val_loss did not improve from 0.54555
  Epoch 3/20
  2774/2774 [==============================] - 169s 61ms/step - loss: 0.5119 - acc: 0.7928 - val_loss: 0.5455 - val_acc: 0.7674
  
  Epoch 00003: val_loss improved from 0.54555 to 0.54549, saving model to model-tgs-salt-1.h5
  Epoch 4/20
  2774/2774 [==============================] - 170s 61ms/step - loss: 0.5117 - acc: 0.7928 - val_loss: 0.5715 - val_acc: 0.7674
  
  Epoch 00004: val_loss did not improve from 0.54549
  Epoch 5/20
  2774/2774 [==============================] - 169s 61ms/step - loss: 0.5126 - acc: 0.7928 - val_loss: 0.5566 - val_acc: 0.7674
  
  Epoch 00005: val_loss did not improve from 0.54549
  Epoch 6/20
  2774/2774 [==============================] - 169s 61ms/step - loss: 0.5138 - acc: 0.7928 - val_loss: 0.5503 - val_acc: 0.7674
  
  Epoch 00006: val_loss did not improve from 0.54549
  Epoch 7/20
  2774/2774 [==============================] - 170s 61ms/step - loss: 0.5103 - acc: 0.7928 - val_loss: 0.5444 - val_acc: 0.7674
  
  Epoch 00007: val_loss improved from 0.54549 to 0.54436, saving model to model-tgs-salt-1.h5
  Epoch 8/20
  2774/2774 [==============================] - 169s 61ms/step - loss: 0.5137 - acc: 0.7928 - val_loss: 0.5454 - val_acc: 0.7674
  </code></pre>