Intrada ALPR Documentation

Camera Setup

Please find below some basic rules of the thumb for achieving optimal recognition results.

  • Rotation: The camera should be mounted in such a way that in the resulting image of a single line license plate a horizontal line can be drawn which crosses both the left edge and the right edge of the license plate.
  • Vertical angle: The maximum vertical view angle of the camera is 30 degrees.
  • Horizontal angle: The maximum horizontal view angle of an camera is 25 degrees. In most systems the horizontal angle is somewhere between 15 and 20 degrees.
  • Plate position: Ideally, mount the camera in such way that an image of the license plate is captured where the license plate is in the center of in the recorded image.
  • Occlusion: Avoid possible blocking objects in the view path of the camera such as (moveable) bars.
  • Contrast: For contrast we use the difference in 8bit gray levels between the characters at the license plate and the license plate background. This difference should be at least 15.resolution_example
  • Resolution: For resolution we use the term pixels per stroke to define a minimum requirement for reliable ALPR. The image on the right shows what is meant with stroke. Because the stroke width is country and platestyle dependent we do not use pixels/cm. In general the resolution for best ALPR performance should be at least 2.7 pixels/stroke.

In addition, blurring introduced through high compression or motion should be prevented at all times. Any image quality requirements not met may impact the performance of the ALPR engine.

Troubleshooting Guide

Q1 Which product are you using?
  • Intrada ALPR: move to Q2
  • Intrada Live: TBW
Q2 How are you using Intrada ALPR?
The end-goal is to use the API for integration with your own applicaton. But we provide a Visualizer that allows you to reproduce recognition outside of your own context.
  • Intrada Visualizer: move to Q3
  • Through API: TBW
Q3 Does the Visualizer startup correctly?
After starting the Visualizer application, do you see a screen with in the bottom-right a blue round “i” button that can be clicked?
  • Yes: TBW
  • No: move to Q4
Q4 What is the error message?
You should notice a “failure” popup with an error message in the top row.
  • Cannot find license file: Please check the possible solutions as provided.
  • The license file is invalid: Please make sure you are using the original license file as provided by Q-Free.
  • The license file is expired: Please make sure you are using the latest license file as provided by Q-Free. If you do, please contact Q-Free for assistance.
  • The Intrada library was not found: Please check the possible solutions as provided.
  • None of the country modules could be found: Please check the possible solutions as provided.
  • Other: Please contact Q-Free for assistance.