Requirements for Optimal LPR

  • License plates must be clearly visible, with the entire plate within the frame of the image
  • All characters must be visible, unobstructed, and undamaged
  • The image is sharp, not blurry, with little distortion/noise (high compression is not recommended), and not overexposed
  • Camera angle should be offset less than 30 degrees in a single plane (horizontal or vertical, but not both) wherever possible
  • Characters must appear at least 16 pixels in height (for the Roman alphabet, others may require 20 pixels) and at least 2 pixels wide
  • Characters should be no taller than 50 pixels

Get the Most out of Licentia

For maximum accuracy, camera angles should be directly in front of plates or offset less than 30 degrees (less than 15 degrees for optimal performance) in either horizontal or vertical directions. Simultaneous offset in both the horizontal and vertical should be avoided wherever possible.

Licentia can read the plates from images taken in various conditions. However, to achieve a 98% or better recognition rate with short recognition times, the camera must be positioned in accordance with Aventura recommendations (as stated here). Smaller angles of offset will result in superior recognition rates.

The Importance of Distance

The distance between the camera and plate is also important. If the camera is too distant, the characters may not be large enough to be recognized. In this case, zoom-in until you reach the proper size. With sub-optimal camera placement, some cropping may occur and not all characters will register.

The size of the characters on the image is of paramount importance. For English characters (Roman alphabet) it is recommended to have at least 16 pixel average character height, for Arabic or other special characters it is recommended to have 20 pixel height. Characters that are oversized are not suitable for LPR, therefore try to avoid settings where the character size is greater than 50 pixels in height. Line width of characters on the image should be at least 2 pixels.