Security Sales & Integration March 2023 - 58

Video
Stepping Up to
the License Plate
Among the ways LPR (sometimes
called automatic number
plate recognition) solutions
are being used include parking
enforcement, law enforcement
and general security.
software in detecting the presence of a license
plate, as well as the accuracy of the optical character
recognition (OCR). While many LPR
software providers will share data on OCR accuracy,
it is only relevant if the software is first
highly accurate at detecting the presence of a license
plate in an image. If the software does not
detect the presence of a plate with a high degree
of accuracy, it decreases the overall capture rate
and effectiveness of the solution.
Other features to review include the countries
and state license plates supported by the
software, and the ability to manage and match
white, black or information lists with operator
alerts based on these lists. The capability
to conduct forensic searches of vehicles for
post-analysis of events and the possibility to
embed the software in other management systems
for greater efficiency are also important.
Information useful to record in these solutions
includes date and time of capture, direction
of movement, plate number, and information
on a match with the white, black, or
information lists of predefined vehicles. With
blacklists, operators can be notified immediately
if a known license plate is detected by a
camera. Once notified, the operator can trigger
a nearby moving camera to track the vehicle
and provide security personnel the visual
information they need to respond quickly and
accurately.
Integration with third-party information
If the software
does not detect
the presence
of a plate with
a high degree
of accuracy, it
decreases the
overall capture
rate and
effectiveness of
the solution.
58
sources can also help to identify a stolen vehicle,
insurance status, toll subscription status, or
authorized taxi or service vehicle status. If a vehicle
is identified as a potential risk, searches of
the plate number help operators to see the different
locations of the vehicle over time - providing
an overview of how the vehicle moved
through the area being monitored.
Tools to manage storage and deletion of video
and plate data in compliance with local regulations
is also important.
System Installation Tips
When installing a system, the correct mounting
point and angle of the cameras are essential
for capturing the best license plate images.
Often, the LPR software supplier will specify
maximum camera mounting angles - both
horizontally and vertically. Installation with
angles beyond these limits may reduce the reliability
of the software. For best results, the
horizontal angle should be as small as possiSecurity
Sales & Integration MARCH 2023
ble. While ensuring the vertical angle is within
the LPR software supplier's recommendations,
it is best to mount the camera higher
than the license plate to minimize headlight
glare issues.
The software supplier will also specify the
minimum number of pixels required, horizontally
and vertically, for reliable decoding of the
license plate number. This, combined with the
resolution of the camera and the focal length
of the lens determines the maximum distance
at which the system can retrieve license plate
numbers.
Lens quality is also important, especially in
single camera, multilane applications. Placement
of the camera should ensure enough contrast
on the license plate, and lens distortion
should be low enough to ensure enough pixels
on target are captured for off-center lanes. IR
lighting, required at night, should have an even
light distribution pattern across all lanes.
It is important to also consider the maximum
vehicle speed at which plates can be
decoded for the application to ensure proper
selection of cameras. Maximum vehicle speed
determines the maximum camera shutter
speed. For start-stop applications, an exposure
time of 1/500 second is appropriate, whereas
for speeds of 75 miles per hour, exposure
times of 1/1750 or 1/2500 are more appropriate.
The frame rate of the camera can be
reduced at lower speeds or in start-stop applications,
which in turn reduces the processing
power required for the LPR software.
When choosing the LPR solution, confirm
it can communicate with other systems being
used for security, such as the video management
system (VMS), if it isn't already a native
capability of the VMS. The VMS should be
able to receive alarms from the LPR solution
for real-time notifications of detected vehicles,
ensuring operators only need to work within a
single system - increasing efficiency.
Targeting Markets & Applications
There are a variety of applications for license
plate capture and LPR solutions. In traditional
security applications, LPR solutions are being
used for access control, parking enforcement,
law enforcement and for general security.
Using LPR for facility access control is one
of the growth areas in this segment of the security
industry. It involves monitoring which
vehicles are entering an area and ensuring they
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Security Sales & Integration March 2023

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