Losses and decoders for end-to-end Speech Recognition and Optical Character Recognition with PyTorch

The module focuses on experiments with CTC-loss (Connectionist Temporal Classification) and its modifications.

Under active development.

Documentation

artbataev.github.io/end2end/

Losses

• CTC (C++, CPU)

Decoders

• CTC Greedy Decoder (C++, CPU)
• CTC Beam Search Decoder (C++, CPU)
• CTC Beam Search Decoder with language model (C++, CPU)

How to install

Requirements:

• Python 3.6+
• Tested with PyTorch 1.6.0+ (maybe compatible with other versions)

1. Install PyTorch from pytorch.org, e.g.

   pip install torch

2. Install tools to compile

   sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y && \
   sudo apt-get update && \
   sudo apt-get install libboost-all-dev g++-7 -y

3. Install the module

   pip install -v git+https://github.com/artbataev/end2end.git

   or

   git clone --recursive https://github.com/artbataev/end2end.git
   cd end2end
   python setup.py install
   python -m tests.test_ctc
   python -m tests.test_ctc_decoder

How to use

CTC Loss

import torch
from pytorch_end2end import CTCLoss

ctc_loss = CTCLoss(blank_idx=0, time_major=False, 
    reduce=True, size_average=True, after_logsoftmax=False)

batch_size = 4
alphabet_size = 28 # blank + 26 english characters + space

logits = torch.randn(batch_size, 50, alphabet_size).detach().requires_grad_()
targets = torch.randint(1, alphabet_size, (batch_size, 30), dtype=torch.long)
logits_lengths = torch.full((batch_size,), 50, dtype=torch.long)
targets_lengths = torch.randint(10, 30, (batch_size,), dtype=torch.long)

loss = ctc_loss(logits, targets, logits_lengths, targets_lengths)
loss.backward()

CTC Decoder

import torch
from pytorch_end2end import CTCDecoder

batch_size = 4
alphabet_size = 6
decoder = CTCDecoder(blank_idx=0, beam_width=100, 
                     time_major=False, after_logsoftmax=False,
                     labels=["_", "a", "b", "c", "d", " "])

logits = torch.randn(batch_size, 50, alphabet_size).detach()
logits_lengths = torch.full((batch_size,), 50, dtype=torch.long)

decoded_targets, decoded_targets_lengths, decoded_sentences = decoder.decode(logits, logits_lengths)
for sentence in decoded_sentences:
    print(sentence)

Future Plans

Losses

• Gram-CTC
• CTC without blank (C++, CPU)
• CTC (Cuda)
• CTC without blank refactoring
• Dynamic segmentation with CTC refactoring

Decoders

• Restrict Beam Search with vocabulary
• Allow custom transcriptions
• Gram-CTC Beam Search Decoder