The selection of an appropriate camera can influence the success of an Intelligent Traffic System (ITS) application. Insufficient sensitivity, inaccurate timing, and too much noise can all negatively affect quality and reliability of data provided by an ITS. Various characteristics need to be considered while selecting imaging equipment to ensure data accuracy for applications such as Automated Speed Enforcement, Automated Tolling, and Red Light Enforcement.
The imaging system and its output need to be versatile, reliable, enforceable, and easily operable to successfully perform in the field of ITS. Lumenera was approached by a large ITS solutions vendor to develop a custom imaging system for traffic monitoring with these characteristics.
Figure 1. The right camera can make or break an ITS application.
The camera chosen for any ITS application should have the ability to deliver outstanding performance in various lighting conditions and environments, from standard day/night operation to extreme weather conditions such as fog, rain, and snow. The combination of varying light and changing weather needs to be matched by an imaging system with outstanding dynamic range.
Figure 2. The camera selected for any ITS application must be able to perform in a wide range of environments and lighting conditions.
This measurement is generally presented in decibels and is the ratio of the number of electrons that can fill one pixel to the number of average noise electrons that exist. The higher the camera's dynamic range, the larger the variations between bright and dark the camera can interpret in a single frame.
This should not be confused with the Quantum Efficiency (QE) of a camera, an equally significant parameter in low light detection. QE is the percentage of photons that reach the sensor of the camera and are transformed into electrons. A camera with a higher QE exhibits more sensitivity to light.
An ITS solution needs to be enforceable under the legislation of the local jurisdiction to become viable. For example, in some states in the US, a red light violation should be accompanied with the video footage of the incident as well as the dated and time stamped images of the violation.
For this purpose, the ITS vendor required a more deterministic triggering mechanism over its consumer-level DSLR in order to lower the 250 ms latency experienced by it. It also needed a camera with a resolution good enough to capture images of multiple lanes of traffic while taking a clear picture of the licence plates for Automated Number Plate Recognition.
These high resolution images must be free from smearing or blurring, a typical problem experienced by rolling shutter cameras while taking images of fast moving vehicles. High resolution, blur-free images were achieved by using the Lt16059HC that is equipped with a high-resolution image sensor and an electronic global shutter, which allows each pixel to be exposed at the exact same time.
Figure 3. Jacques Henri Latrigue’s photo of a race car taken in 1912 demonstrates the skew generated by a rolling shutter on a fast moving object.
The ITS vendor experienced failures following merely 100,000 shutter actuations with their DSLRs, and this prompted it to seek a more powerful solution. The manufacturer’s warranty will become invalid if a consumer product is used for an industrial application.
It is essential to use industrial grade cameras for ITS applications. Industrial cameras generally feature electronic shutters, which are less prone to failure due to the absence of a moving mechanical components. They are also engineered for continuous use to reflect the intended operation of the application in a better manner, and have associated warranties.
Ease of Use
A camera that can be operated with minimal configuration and integrated into an ITS application is more suitable for this application. The application can be rapidly deployed with minimum effort using a standard plug-and-play interface like the USB 3.0.
The drivers of the camera, SDK and API, must also be powerful and intuitive to allow for stable integration with the operating system of the application. The ITS vendor reauired a camera with little physical impact on the area of installation. The camera and any additional instrument must be placed in a single enclosure.
The Right Fit
Lumenera’s Lt16059H was chosen for this specific application due to its 16 MP resolution (4864 pixels wide x 3232 pixels high). This feature enabled the ITS vendor to monitor four to five lanes of traffic simultaneously using a single camera. The Lt16059H features an electronic global shutter and a 35 mm OnSemi KAI-16070 CCD sensor to help minimize blurring and smearing.
With the larger pixel size of 7.4 x 7.4 µm, it is ideally suited for low light conditions. Each pixel has a full well capacity of roughly 33,700 electrons. It is equipped with an industry-leading low read noise of 15.5 electrons, thus exhibiting an outstanding dynamic range of roughly 67 dB.
The Lt16059H can capture a high amount of details in scenes with high variations in lighting to generate images that are completely enforceable as traffic violations. It can provide this level of enforceability, as the image processing is taking place within the camera itself (Figure 4). No additional software is required for post-processing the images captured.
Figure 4. Pre-processing the images inside the camera brings out information that would otherwise be lost while remaining enforceable images for evidence purposes. (Top Photo: Before pre-processing, Bottom Photo: After pre- processing)
Lumenera’s team of engineers in collaboration with the ITS vendor’s software group developed an auto calibration algorithm, which allowed the camera to take multiple sample images every 5 minutes to manipulate its iris, exposure, and gain values under varying lighting and weather conditions.
With this process in place, the camera was able to use the optimum settings to take precise and enforceable images and at the same time, it retained the ability to receive a trigger to record a violation. This process also provided a reduction of latency of approximately 5 to 7 ms in comparison with the earlier DSLR camera, yielding reliable and reproducible results.
The Lt16059H can software trigger through a video feed for a minimalist installation approach. The camera is also capable of self-triggering through software based rules, minimizing the need for external triggering mechanisms such as ground loop.
It can also be triggered through a near-zero latency opto-isolated GPIO in the presence of pre-existing infrastructure, such as a RADAR or LIDAR detector. Compared to DSLR cameras, these triggering mechanisms are much faster and are highly reliable to guarantee that the vehicle will be positioned in the exact position of the frame while triggering the camera.
The Lt16059H camera features a Canon EF lens mount (Figure 5), which was another key reason behind the selection of the camera for this application. The camera also features a fully integrated Canon EF lens controller, which eliminates the need for any external cabling by offering flexibility through remote control.
As a result, the ITS vendor was able to control the focus and iris of the lens remotely and automatically through the API. A reliable connection is ensured with the host computing platform for deployments susceptible to shock and/or vibrations by locking GPIO and USB 3.0 connectors.
Figure 5. Another key element to the selection of the Lt16059H camera for the ITS vendor’s application was the camera’s Canon EF lens mount.
Key Features of Lt16059H
The following are the key features of the Lt16059H camera:
- Quad tap design for ultrafast frame rates (12 fps at full resolution)
- High quality ON Semiconductor KAI-16070 CCD sensor offers low smear and outstanding dynamic range
- Canon EF lens mount with fully built-in controller for auto focus/iris supported by Lumenera’s API, improves flexibility and accuracy for remote applications
- Fanless body, compact, and low power consumption
- Global electronic shutter captures superior quality, high-speed images without blur
- Zero loss 256 MB RAM frame buffer for reliable image delivery in challenging conditions
- Stable and reliable USB 3.0 device drivers facilitate control of full streaming uncompressed video and still image captures
The ITS vendor selected Lumenera’s Lt16059H as the ideal imaging system for its application as the camera is versatile, reliable, accurate and user-friendly, in addition to having an industry-leading four-year warranty.
This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.
For more information on this source, please visit Lumenera Corporation.