Answer-Sheet-Extraction

Vietnamese High School Graduation Examination Answer Extraction using openCV-python

Table of Contents

1. Answer sheet template
2. Installation and run
3. APIs
4. Docker
5. Algorithms
6. References

Answer sheet template

Installation and run

1. Clone repository
2. Run pip install -r requirements.txt
3. Change the image path in tools/pipeline.py
4. Run python tools/pipeline.py

Notes

• Highly recommend using conda/miniconda for avoiding evironments conflicts.
• Test specific features? use the code in tools/

APIs

1. Running using uvicorn app:app --port 1234
2. Test API via Swagger UI: localhost:1234/docs

Containerization

1. Download and install Docker
2. Have a look at Dockerfile
3. Build image docker build -t VNASE .
4. Run container docker run -d --name vnase -p 80:80 VNASE
5. Test API via Swagger UI: localhost/docs

Algorithms

Input: Answer sheet captured image

Output: List of answers, student ID and exam code

Sample input:

Solution:

• Phase 1: Image preprocessing

  • Remove background (using GrabCut)

  

  • Paper contour detect

  

  • Perspective transform

  

• Phase 2: Extraction

  • Answer extraction:

    • Preprocess: crop - convert to grayscale - remove noise - erore and dilate

    

    • Detect answer boxes

    

    • Extract answer by create a grid on template (have a look at grid.py)

    

    • Threshold each answer bubles to decide if an answer was selected or not. (by counting non-zero pixel)

      • Not selected:
      • Selected:

  • Student ID and exam Code:

    • Preprocess: crop - convert to grayscale

    

    • Threshold - erore and dilate

    

    • Detect selected bubbles - calculate output based on bubbles position

References

1. https://learnopencv.com/automatic-document-scanner-using-opencv/
2. https://docs.opencv.org/3.4/da/d22/tutorial_py_canny.html
3. https://docs.opencv.org/3.4/d4/d73/tutorial_py_contours_begin.html
4. https://www.analyticsvidhya.com/blog/2022/08/image-contrast-enhancement-using-clahe/
5. https://docs.opencv.org/3.4/db/df6/tutorial_erosion_dilatation.html
6. https://www.mathworks.com/help/visionhdl/ug/contrast-adaptive-histogram-equalization.html
7. https://docs.opencv.org/3.4/d8/d83/tutorial_py_grabcut.html
8. https://docs.opencv.org/3.4/da/d6e/tutorial_py_geometric_transformations.html