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.
The default Latin-based OCR equivalent characters are the following:
- 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”.
Best Practice: Do not allow more than two OCR equivalent characters because it
results in too many false-positive matches.
The following example uses a hotlist with the ALPR matcher configured to allow for one
OCR equivalent character:
- 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 also.
- 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.