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Handwritten-Chinese-OCR

Summary

This project aims to create a simple and unified handwritten text-line recognition reference solution using CNN-only and CTC method with PyTorch framework and Intel OpenVINO toolkit. And it is also the source of multiple previous works including:

• Offline Handwritten Chinese Text Recognition with Convolutional Neural Networks (arXiv 2020)
• Searching from the prediction of visual and language model for Handwritten Chinese Text Recognition (ICDAR 2021)
• OpenVINO Open Model Zoo: handwritten-simplified-chinese-recognition-0001

The overview of our method to predict and decode the result with visual and language model.

Comparison with recent works on the ICDAR 2013 competition set in the metric of character error rate (100% - AR).

Part I: Start from the pre-trained models with Intel OpenVINO toolkit

Installation

• Anaconda with Python 3.7 or above (recommended)
• Intel OpenVINO toolkit with version 2021.3 or above

Inference

Download the models trained with SCUT-EPT dataset with Open Model Zoo downloader tool.

python <your-openvino-installation>/deployment_tools/open_model_zoo/tools/downloader/downloader.py \
       --name handwritten-simplified-chinese-recognition-0001

Run inference with the SCUT-EPT test image as input and check the prediction.

# use character list for SCUT-EPT data instead
# https://github.com/openvinotoolkit/open_model_zoo/blob/master/data/dataset_classes/scut_ept.txt
# NOTE: input data was not normalized during the SCUT-EPT model training
python deploy.py -lang hctr -m <path-to-handwritten-simplified-chinese-recognition-0001.xml> \
       -dm greedy-search -i <path-to-input-image>

Input and output examples (NOT use language model, and only use VGG-based network for training this recognition model):

['仍有“铁马冰河入梦来”的情怀，一生心忧天']

['不祇辱于奴隶人之手']

['④自己独自漂泊的孤独之感。人语朱离逢山峒獠”此句可体现。']

['婆婆是受了马骗。⑤阿苦担心家人的身体健康，怕闸蟹吃了会生游。']

['马克思主义者．']

Part II: Reproduce this paper work with CASIA-HWDB databases or train new models with your own data

Installation

• Anaconda with Python 3.7 or above (recommended)
• PyTorch 1.8.1 or above
• NVIDIA CUDA 11.0 or above
• NVIDIA Apex library
• PyTorch Binding for warp-ctc

Dataset and Structure

Restricted datasets for research only for different languages:

• CASIA-HWDB
• Kondate
• IAM

The format of train/val/test_img_id_gt.txt are designed as one sample per line, which uses a comma to separate the image and label:

img_id_1,text_1
img_id_2,text_2
img_id_3,text_3
...

The format of the chars_list.txt is designed as one character per line:

character_1
character_2
character_3
...

Training

Note that, before training with a target dataset, all the gray-scale images should be resized to fixed-height (e.g. 128) with fixed-ratio.

python main.py -m hctr -d <path-to-dataset> -b 8 -pf 100 -lr 1e-4 --gpu 0 (default: multi-gpus mode)

Testing

After the training, the model can then be tested with testset or single image for benchmarking. In order to get the output of CTC-based text recognition, there is one additional step called decoding which is ensential for final accuracy.

python test.py -m hctr -f <path-to-trained_model> \
               -i <input_image> (or -ts <path-to-testset>) \
               -dm [greedy-search|beam-search] \
               ...

Decoding with greedy-search

This is a basic and default decoding method, and it only takes the maximum probalitiy at each output step.

Decoding with beam-search (with language model)

To further improve the accuracy, a specific language model (n-gram or transformer-based) can be introduced to work with the beam-search decoding. There are two major strategies provided to configurate the beam-search.

• For the best accuracy, adding:

  -dm beam-search --use-tfm-pred --transformer-path <path-to-trained-tranformer>

• For the shortest latency, adding:

  -dm beam-search --skip-search --kenlm-path <path-to-trained-ngrams>

See the instructions under third-party folder to train a specific n-gram or transformer-based language model.

Deploying

1. Convert the PyTorch model to onnx with export_onnx.py
2. Convert the onnx model to OpenVINO IR xml and bin (optional)
3. Inference with OpenVINO on target platform with deploy.py
4. Tune the performance with best known practises.

License

Handwritten Chinese OCR Samples is licensed under Apache License Version 2.0.

Citation

If you find this code useful in your research, please consider citing:

@article{bliu2020hctr-cnn,
      Author = {Brian Liu, Xianchao Xu, Yu Zhang},
      Title = {Offline Handwritten Chinese Text Recognition with Convolutional Neural Networks},
      publisher  = {arXiv},
      Year = {2020}
}