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License plate recognition camera

How to select and install license plate recognition camera?

How to choose and install license plate recognition (LPR) system? The overall performance is determined by many factors such as mounting angle, distance and shutter speed setting, which are critical for deploying an LPR camera. In the past years, license plate recognition application has becoming popular in video surveillance field such as traffic monitoring, packing lot access, law enforcement, automatic toll payment, etc. 

To get a high confidence level of plate recognition, a lot of factors such as camera selection, suitable lens selection, artificial lighting and installation position shall be studied before placing a purchasing security cameras. Otherwise, a good result is unexpected. In this article, we will focus on the rules how to determine the installation position of camera and how to select suitable illuminator to obtain a clear image for license plate recognition, with SCR515PRO as an example. Also some key parameters setting of cameras for getting a clear image for LPR are recommended in the final section.

LPR Preparation

Taking SCR515PRO as an example, the camera’s built-in 7.5~50mm lens can capture a width of field about 13~16 ft.

Car License Recognition

To ensure an optimal license plate image, please adjust the lens under the conditions we suggest. (NOTE: The license plate image shall be 18% width of the screen for good license plate recognition.)

The recommended capture distance is 49-100 ft. (15-30m) for a reflective plate and 33-82 ft. (10-25m) for a non-reflective plate.

PLR Installation

1. The camera height should be higher than 11.5 ft. (3.5 m)   

2.  The width of the license plate should occupy approximately 17~20% of the width of the screen.

3. Vertical angle should be NO less than 40 degrees

LPR Installation Diagram

IR Illuminators Selection

If the built-in IR light is not enough to get clear image on field installation, an additional illuminator is required. Here we point out two key items that shall be considered when selecting IR illuminator.

1. The LED beam angle:

Assume the target distance = 6-8m and width of target = 1.72m; we can use the triangle formula below to calculate the required beam angle to cover the whole width.

Beam angle required= Angle Calculation Formulathat means you have to select a illuminator with beam angle > 12∘.

2. The LED illuminating distance:

In general, the projecting distance of an illuminator is specified at the condition of image captured under 1/50”(or 1/60”) shutter speed. However, the shutter speed usually is set to 1/1000” for license plate capturing, so we have to calculate the distance with this factor taken into consideration.

Distance calculation formula

Camera Parameters Setting

Good image quality is the key to succeed in LPR application, in which good contrast, no overexposure and no blur on image are three major factors that shall be strongly emphasized and followed.

1. SCR515PRO:

(1). Choose “CATCH ALL” to enter the settings

Messa Camera LPR Setting

(2). Refer to the table below to set best parameters, especially for LUMII and SHUTTER.

Messa Camera LPR Setting
Easy Mode NORMAL
LUMII Level4
GAMMA Level4 
HLC Level4 

2. LPR IP Camera - LPR606

In camera web Setup page, Image > Exposure > Exposure Mode, select Manual Exposure.
Refer to the table below for recommended setting.

Messa Camera LPR Setting - LPR606
Day Exposure Time 1/250
Night Exposure Time 1/250
Manual Lumii 0-5 (low is better to avoid noise)

3. LPR610/615:

In camera web Setup page, select ANPR/LPR. Refer to the table below for recommended setting.

Messa Camera LPR Setting - LPR610/615
Traffic User
Exposure Mode Auto IRIS Mode
Manual Exposure Time  1/250s, and higher is required for higher vehicle speed
Manual Gain 0-4 (low is better to avoid noise)
Don’t choose Max Gain
ICR Control External mode (with default Alarm port=1,
Active=LOW), implying the day/night is controlled by an external illuminator

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