Proof of concept reading of punched cards using photos of punched cards and OpenCV. If one has a stack of punched card, the idea is to take photos of each card (without having to be too careful about orientation and perspective) and use this program to read them.

Currently only works with one specific type of card:

Run code

> python3 readcard.py test-cards/card.jpg
      CALL RCLASS(AAA,21,NNC,PX3,PX4)
> python3 readcard.py test-cards/card-rotated.jpg
      CALL RCLASS(AAA,21,NNC,PX3,PX4)
> python3 readcard.py test-cards/card-perspective.jpg
      CALL RCLASS(AAA,21,NNC,PX3,PX4)

Basic outline of how it works

1. Find upper left corner (the diagonally cut corner) by checking which corner that has most background pixels.

2. Now that we know the orientation of the card, use a grid approach to go through each potentially punched position to see if it is punched or not, again by counting background pixels. Each column forms a bit pattern.

3. Match this bit pattern with a fixed 64 character map (different punched cards can have different maps).