FCN - Build the TensorFLow loss and optimizer operations.

optimize.py

def optimize(nn_last_layer, correct_label, learning_rate, num_classes):
  
  # Reshape 4D tensors to 2D, each row represents a pixel, each column a class
  logits = tf.reshape(nn_last_layer, (-1, num_classes), name="fcn_logits")
  correct_label_reshaped = tf.reshape(correct_label, (-1, num_classes))

  # Calculate distance from actual labels using cross entropy
  cross_entropy = tf.nn.softmax_cross_entropy_with_logits(logits=logits, labels=correct_label_reshaped[:])
  # Take mean for total loss
  loss_op = tf.reduce_mean(cross_entropy, name="fcn_loss")

  # The model implements this operation to find the weights/parameters that would yield correct pixel labels
  train_op = tf.train.AdamOptimizer(learning_rate=learning_rate).minimize(loss_op, name="fcn_train_op")

  return logits, train_op, loss_op