Defined in tensorflow/python/ops/

See the guide: Neural Network > Connectionist Temporal Classification (CTC)

Performs greedy decoding on the logits given in input (best path).

If merge_repeated is True, merge repeated classes in output. This means that if consecutive logits' maximum indices are the same, only the first of these is emitted. The sequence A B B * B * B (where '*' is the blank label) becomes

  • A B B B if merge_repeated=True.
  • A B B B B if merge_repeated=False.


  • inputs: 3-D float Tensor sized [max_time, batch_size, num_classes]. The logits.
  • sequence_length: 1-D int32 vector containing sequence lengths, having size [batch_size].
  • merge_repeated: Boolean. Default: True.


A tuple (decoded, neg_sum_logits) where * decoded: A single-element list. decoded[0] is an SparseTensor containing the decoded outputs s.t.: decoded.indices: Indices matrix (total_decoded_outputs, 2). The rows store: [batch, time]. decoded.values: Values vector, size (total_decoded_outputs). The vector stores the decoded classes. decoded.dense_shape: Shape vector, size (2). The shape values are: [batch_size, max_decoded_length] * neg_sum_logits: A float matrix (batch_size x 1) containing, for the sequence found, the negative of the sum of the greatest logit at each timeframe.