Security Sales & Integration January 2022 - 47

once you focus it down to get the pixel count
necessary to accurately read license plates, the
camera no longer provides the overview it was
intended to capture.
Most surveillance cameras are not designed
to capture details as specific as numbers and
letters on a license plate. They typically use
low-cost rolling shutters instead of higher
performance global ones. This can result in
reduced read accuracy at night, at high speeds,
and under a variety of weather conditions.
One solution to this problem is to install
an additional surveillance camera to ensure
that the area is covered properly. In the end,
however, instead of saving money by using one
camera for two purposes, costs are increased because
you have to purchase the server and software
license necessary to read the license plate
as well as any additional cameras that are not,
ultimately, purpose-built for the task.
Data Lost in Transmission
Another problem with server-based ALPR is
that the raw footage from the camera has to be
transmitted to the server for processing. The
recurring costs associated with transferring all
the data necessary for the server to get a good
read of a plate can be high, especially if it is
being sent over a cellular network. Given the
fact that surveillance cameras transmit a constant
video stream even when no vehicles are
present, it becomes clear how expensive server-based
ALPR can be.
This process of moving data is also prone
to transmission problems. If communication
between the camera and server is interrupted
or dropped, the footage disappears and can't be
used for real-time identification. It also means
that the data won't be available for any postevent
investigation because, when the transmission
is interrupted for any reason, the video is
lost as nothing is stored on the camera.
Advantages of Edge-Based Systems
The main difference with edge-based license
plate recognition is that it uses ALPR cameras
purpose-built to read license plates. With this
solution, the algorithm that processes the raw
video stream and reads the license plate is in
the camera itself.
One key advantage of using purpose-built
technology instead of adapting video surveillance
cameras is the increased accuracy in license
plate reads. With an edge-based ALPR,
securitysales.com
end users get a system that is designed to address
their specific license plate recognition needs.
In many jurisdictions, the variety of plate
designs can make it difficult for traditional security
cameras to get an accurate image. Plates
can be flat or embossed and can have different
reflective values. All of which can impact the
quality of the image capture. And, if the camera
is not able to capture a clear image of the plate,
then the processor will not be able to make an
accurate read.
Shutter speed plays an important role in capturing
good quality images. With traditional
image-making, the shutter speed controls how
long the lens is open to incoming light. When
the shutter is open longer, more light gets in.
The same is true with ALPR. If the shutter isn't
open long enough, images can be too dark to
read; if it's open too long, images can be flooded
with light or blurry because of vehicular motion,
which also makes them difficult to read.
In a purpose-built ALPR camera, the shutter
speed is constantly adjusted to compensate for
different lighting conditions. For example, an
ALPR camera taking 30 images a second will
adjust its shutter speed for every one of those
images. This is because the goal is not to take the
clearest picture of the surroundings but to capture
the most accurate image of a license plate.
The camera works in conjunction with
the firmware to adjust the illumination and
shutter speed to get the best image for an
accurate read. After taking several pictures
with different shutter speeds, the camera goes
through the images to find the one with the
highest quality and then gives that image to the
camera processer to read the license plate.
Law enforcement and parking
were the first verticals to adopt
ALPR cameras and systems.
The police started using ALPR
technology in patrol cars
to read license plates and
compare them with a hotlist of
wanted or stolen cars. Parking
enforcement then adopted the
technology to help manage
permits and identify parking
violations.
Most surveillance
cameras are
not designed to
capture details
as specific as
numbers and
letters on a
license plate.
JANUARY 2022 Security Sales & Integration 47
AMINKOREA/ADOBE.STOCK.COM
http://www.securitysales.com
Security Sales & Integration January 2022

Table of Contents for the Digital Edition of Security Sales & Integration January 2022
