The ALPR matcher uses the Optical Character Recognition (OCR) equivalence technique to improve plate read accuracy rate.
Depending on the font design, some plate characters can look very similar to other characters. These are called "OCR equivalent characters".
You can configure how the ALPR matcher handles OCR equivalence by modifying the MatcherSettings.xml file. For more information, see MatcherSettings.xml file.
- Number of character differences (see ALPR matcher technique: Number of character differences)
- Common and contiguous characters (see ALPR matcher technique: Common and contiguous characters)
- The number “0” and the letters “O”, “D”, and “Q”.
- The number “1” and the letter “I”.
- The number “2” and the letter “Z”.
- The number “5” and the letter “S”
- The number “8” and the letter “B”.
- The number “6” and the letter “G”.
The ALPR matcher finds the exact match ABC123 in the hotlist and raises a hit. It also looks for any plates that are one OCR equivalent character off, and finds A8C123, ABC1Z3, and ABCI23 in the hotlist, so it raises hits on them as well.
If the ALPR matcher found the plate A8CIZ3 (three OCR equivalent characters off), it would not raise a hit because the system is configured to accept a maximum of one OCR difference.