Vietnamese Handwritten OCR (Top5 Kalapa Challenge 2023)

Problem Statements

• Problem: Building a lightweight model suitable for mobile devices to perform Vietnamese Handwritten OCR in the context of Vietnamese addresses

• Input: Raw image with one line text
  
  
  
  

• Output: the text in the input image

• Metric: the custom of edit distance between output with lable

• Requirements:

  • Model size <= 50mb
  • Inference time <= 2s
  • No pretrained model for OCR task or handwritten dataset

• Some issues with data:

  • White space at the end of the image.
  • Short text lacking linguistic context.
  • Excessive use of colors.
  • Two lines of text.
  • Text not fully visible.
  • Empty images.

• Ideas:

  • Choose a very lightweight OCR model: SVTR
  • Train a pretrained model with generated data
  • Finetune on the real dataset

Prepare data:

|___data
|    |___train
|    |    |___images
|    |    |    |___0.jpg
|    |    |    |___...
|    |    |___labels
|    |    |    |___0.txt
|    |    |    |___...
|    |___val
|    |    |___images
|    |    |    |___0.jpg
|    |    |    |___...
|    |    |___labels
|    |    |    |___0.txt
|    |    |    |___...

Pretrained

• Collect address text:

  • Extract data from an Excel file provided by the government.
  • Get text label from other OCR datasets
  • Crawl information on villages from Google.

• To generate data, use some handwritten fonts and the text corpus to generate with my repo OCR-Handwritten-Text-Generator

• Then, apply some augmentation in above repository

• Total: 250k - 350k images

Finetuned

• Manually check to crop 2 line image and correct the label

• To crop image to remove the white part at the end, help handle the empty image

python3 main.py --scenario preprocess \
--raw_data_path "./path/to/raw/data/"

• Then, create lmdb data from raw data:

python3 main.py --scenario create_lmdb_data \
--raw_data_path "./data/OCR/training_data" \
--raw_data_type "folder" \
--data_mode "train" \
--lmdb_data_path "./data/kalapa_lmdb/"

• Flag:
  • raw_data_path: path to raw data
  • raw_data_type: have 3 values:
    • json: a dir contains image and a json file with each line contains path to image and text label.
    • folder: a dir contains image subdirs and a dir contains subfile .txt label.
    • other: the second gen type from my repo.
  • data_mode: train data or eval data
  • lmdb_data_path: path to output lmdb data

Trainning

• To run training:

python3 main.py --scenario train \
--model SVTR \
--lmdb_data_path "./data/kalapa_lmdb/"
--batch_size 16
--num_epoch 1000

• To run inference test:

python3 main.py --scenario infer --image_test_path "path/to/image.jpg"

Postprocess

• To handle some cases that not show fully sigh or very ugly text, or model is wrong -> decode using beamsearch with ngram model
• To build ngram model from the text file generated from the preprocess part, go https://github.com/kmario23/KenLM-training

Export Onxx

• To export model to onnx (optional):

python3 export_onnx.py

Submission

• To run infer with a folder:
  • run in batch:

    python3 submission.py

  • run each image:

    python3 torch_submission.py

  • run each image with onnx:

    python3 onnx_submission.py