There are two types of license plate recognition (LPR) cameras on the market: true LPR cameras and standard security cameras that are capable of reading license plates.
True LPR cameras usually cost over $1000 minimum, have tested daytime and night-time reads of license plates on vehicles traveling at certain speeds, and have the ability to interface with some type of software database which has some type of reporting function. They are generally able to read license plates on one or more lanes of vehicles traveling at highway speeds and have some type of built-in or optional diffusable infrared to illuminate the license plate but not over-illuminate to the point where the reflection is all that is seen. Popular manufacturers of LPR cameras in this category include Messoa and Vivotek. Dahua offers ANPR (or automatic number plate reader) cameras, but as of the date of this post, Dahua’s offering only includes the reading of license plates (LPs) of vehicles which are stopped at gates; not moving vehicles. Hikvision is currently still working on their offering.
Most consumers and small to medium-sized businesses would rather spend no more than a few hundred dollars per camera to be able to read license plates of vehicles going in and out of their driveways, streets and intersections, or entry/exit points, also known as choke points. Infrared is generally not diffusable at this price range. These “fake LPR cameras” are not designed for LPR, so vehicle speeds have not been tested, nor has the effective range or number of lanes.
Configuration of cameras to be able to read LPs in daytime and night-time include adjusting frame rate, exposure, and lighting to coincide with vehicle speeds. In 2016 eDigitalDeals was asked by an HOA in the upscale neighborhood of Bel Air, CA to install LPR cameras in two intersections leading into this residential neighborhood to help prevent crime in this area, as well as to identify the owners of vehicles used in conjunction with the home burglaries and home invasions. In the summer of 2017, eDigitalDeals replaced three analog SD single-lane LPR cameras with 3MP IP dual-lane LPR cameras by Messoa during an industrial installation in Fullerton, CA. Photos will posted at the end of this article.
Ten factors to consider when researching LPR cameras:
- Price or budget. This is the most important factor because if the budget is not at least $1000, then either the end-user expectations need to be adjusted, or the budget needs to be raised.
- Reporting and integration. In addition to using some kind of DVR or NVR, there are LPR or ANPR software options on the market that compile a database of vehicle license plates that allow for reporting. Standard reporting features typically include the ability to list or filter license plates beginning or ending with certain characters, blacklisting certain license plates (for example former employees at a company or expelled students at a school), and counting or listing the number of times a vehicle plate has been identified in a given period of time. Our preferred choice of reporting is Milestone XProtect’s LPR.
- Output format. There are several types of camera formats on the market: Analog SD (standard definition), HD-SDI, EX-SDI, HD-TVI, HD-CVI, AHD, and IP are the most common. There are several variations of the analog HD formats (TVI, CVI, AHD), separating the various resolution options. For example, HD-TVI 4.0 identifies HD-TVI cameras up to 5MP, while HD-TVI 3.0 identifies HD-TVI cameras up to 3MP. Choose the format that is compatible with your recorder and/or LPR software.
- Angle, distance, and installation location. It is important to install the camera as close as possible to being perpendicular to the vehicle’s license plate. This means a head-on angle. The more off-to-the side the LPR camera is installed, the lower likelihood of getting a clear reading. If a plate is not read clearly, then it is of little to no use. The most effective horizontal angle is no more than 15-degrees. The maximum vertical angle should be no more than 30-degrees. If the camera needs to be installed higher, for example on a highway or road, it should be capturing plates at a farther distance. If capturing plates at a vehicle stopped at a gate, it’s a best practice to install the camera(s) as close as possible to vehicle license plate height (while considering environmental conditions mentioned below in numbers 8 and 9).
- Lighting and exposure. For the highest chance of LP readings, LPR cameras should be configured in black and white. The faster the vehicle moves, the faster the exposure. For vehicles moving up to 35 MPH, the exposure should be lowered from a default of 1/30 to 1/500. Keep in mind, when the exposure time is lowered, the less light passes through the camera’s lens, and the more infrared light is required. For “fake LPR cameras,” the amount of light passing through to the camera is so low at 1/500 exposure rate that the camera will be nearly black after the sun sets. It would be best to keep a fake LPR camera in night or infrared mode to achieve best captures throughout the day and night. In addition, if a fake LPR camera has HLC or WDR, both should be enabled. HLC or head-light compensation (also known as HLM or head-light masking) helps to block bright headlights so that a license plate can be read more easily. True WDR or wide dynamic range can help to equalize exposure of reflective surfaces, e.g. sunny asphalt, wet asphalt, etc. Do not confuse WDR with DWDR (digital WDR), as DWDR is not nearly as effective as true WDR.
- As of 2016, a lot of people are using starlight technology for fake LPR cameras because no additional infrared light is required and LPs are displayed in full color. Starlight is more ideal for vehicles traveling at lower speeds. In order to see with Starlight, the camera must have infrared mode disabled.
- Speed and frame rate. For moving vehicles, the frame rate of the camera should be set to 15fps (frames per second) or more. For stopped vehicles, 5fps is more than enough. The faster the vehicle speed, the higher the frame rate.
- Number of lanes. True LPR cameras post the tested number of lanes in the features or specifications. Fake LPR cameras don’t post this information, as they are not designed for LPR purposes. It would be best to test the effective range and angle on a fake LPR camera before deploying it.
- Weather conditions. Over time, there may be a need for a new front cover due to environmental damage from the sun, salt (in marine environments), or wind/water from heavy storms. To help protect against environmental maintenance issues, sun-shields are highly recommended, and you can opt for an IP67 or better water/dust-proof rating. LP readings in wet or snowy conditions will be more difficult to achieve than on clear days.
- Vandal-proofing. Cameras should be vandal-proof (also known as vandal-resistant, impact resistant, tamper-proof, or IK10) whenever possible, especially if installed near arm’s reach. Dahua, ACTi and Uniview have various vandal-proof bullet camera options. Vandal-proof dome cameras should not be used for LPR purposes, as the curved dome cover slightly skews the image enough to result in an LP read that is not as clear as the read from a bullet camera with a flat polycarbonate lens cover.
- Maintenance. Over time, it’s possible that a camera with varifocal adjustable lens may need to be re-focused. It’s a good idea to use a remote focus camera (also known as motorized lens) so that you don’t have to go to the camera to re-focus it. If using a motorized lens camera with Internet access (either to the camera or DVR/NVR), you should be able to login to the camera remotely so that you wouldn’t even have to go to the site to refocus the camera. Ensure ports are forwarded to achieve proper remote access. Additionally, the camera may need cleaning from spider webs or bird nests. An ideal solution is the DotWorkz dome cleaner.
Here is a sample video of a fake LPR camera (ACTi E413) in action. This is a 5MP IP Camera with DWDR. Note that there is no true WDR or HLM, but the 10x motorized lens and vandal-proof body made it a low-cost alternative to our competition, and that is what allowed us to win the bid. Some of the LP reads are not as clean as they could be, and that is mainly due to the fact that the camera is installed to the far right of the sidewalk of this intersection. The customer was happy with the price and performance of the cameras because they can make out plates well enough in both day-time and night-time conditions.
If you would like assistance in calculating ideal megapixels and focal length for your LPR application, please contact eDigitalDeals at 1-310-370-9500 or toll-free at 1-877-DEALS-79 (1-877-332-5779) x1 for Sales. You may also chat with a security professional on our website during business hours at http://edigitaldeals.net, or email us at firstname.lastname@example.org.
By Raymond Shadman
Phone: 877.DEALS.79 or 310.370.9500 x101
Raymond Shadman August 21, 2017
Posted In: Video Surveillance
Tags: anpr camera, automatic number plate reader camera, choose LPR camera, how to buy LPR camera, license plate camera, license plate recognition, license plate recognition camera, lpr camera, LPR camera design, messoa lpr camera, vivotek lpr camera