ALPR matcher technique: OCR equivalence - Security Center 5.10

Security Center Administrator Guide 5.10
Product
Security Center
Content type
Guides > Administrator guides
Version
5.10
Language
English
Last updated
2023-06-12

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.

NOTE: You can also configure the following ALPR matcher techniques in the 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: You should 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:

Hit on ABC123 Does the hotlist contain any plates that are one character off? No hit Hit on A C123 8 Hit on ABC1 3 Z Hit on ABC 23 I Does the permit list contain the plate ABC123? (exact match) Yes Yes Yes Yes No Plate read No

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.

Parent topic: ALPR matcher