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60 lines
2.3 KiB
60 lines
2.3 KiB
"""Contains various CTC decoder."""
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from __future__ import absolute_import
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from __future__ import division
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from __future__ import print_function
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import numpy as np
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from itertools import groupby
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def ctc_best_path_decode(probs_seq, vocabulary):
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"""Best path decoding, also called argmax decoding or greedy decoding.
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Path consisting of the most probable tokens are further post-processed to
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remove consecutive repetitions and all blanks.
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:param probs_seq: 2-D list of probabilities over the vocabulary for each
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character. Each element is a list of float probabilities
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for one character.
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:type probs_seq: list
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:param vocabulary: Vocabulary list.
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:type vocabulary: list
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:return: Decoding result string.
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:rtype: baseline
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"""
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# dimension verification
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for probs in probs_seq:
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if not len(probs) == len(vocabulary) + 1:
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raise ValueError("probs_seq dimension mismatchedd with vocabulary")
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# argmax to get the best index for each time step
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max_index_list = list(np.array(probs_seq).argmax(axis=1))
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# remove consecutive duplicate indexes
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index_list = [index_group[0] for index_group in groupby(max_index_list)]
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# remove blank indexes
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blank_index = len(vocabulary)
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index_list = [index for index in index_list if index != blank_index]
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# convert index list to string
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return ''.join([vocabulary[index] for index in index_list])
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def ctc_decode(probs_seq, vocabulary, method):
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"""CTC-like sequence decoding from a sequence of likelihood probablilites.
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:param probs_seq: 2-D list of probabilities over the vocabulary for each
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character. Each element is a list of float probabilities
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for one character.
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:type probs_seq: list
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:param vocabulary: Vocabulary list.
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:type vocabulary: list
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:param method: Decoding method name, with options: "best_path".
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:type method: basestring
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:return: Decoding result string.
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:rtype: baseline
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"""
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for prob_list in probs_seq:
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if not len(prob_list) == len(vocabulary) + 1:
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raise ValueError("probs dimension mismatchedd with vocabulary")
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if method == "best_path":
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return ctc_best_path_decode(probs_seq, vocabulary)
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else:
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raise ValueError("Decoding method [%s] is not supported.")
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