114 | TRAFFIC MANAGEMENT
The eyes of ITS Cameras are an increasingly important tool in traffic management, driving lens technology to develop accordingly Words | Peter Bhagat, Gardasoft Vision, UK ITS applications can provide great challenges for vision systems. Variations in natural lighting and the speed at which images need to be acquired demand sophisticated approaches to the lighting and imaging system. Many components and control techniques employed in machine vision, such as liquid lenses, P-Iris control, multipulse illumination and intelligent lighting, can bring real benefits for ITS. Vision technology can already be found in ALPR, toll booth control, multilane monitoring, automatic toll license validation, red light violation, traffic enforcement systems, vehicle recognition and identification, vehicle occupancy and speed monitoring.
Revolutionary new technology Liquid lens technology is new capability in imaging. The shape of these lenses can be changed in just milliseconds for extremely fast focus adjustment. By dynamically changing the focus, it is not necessary for the optical system to have a large depth of field, which means that the iris can be wider, giving brighter images. The liquid lens can be used in conjunction with a normal camera lens to adjust the focus of the system. For a 200mm macro lens, the focus can typically be adjusted from 100mm to infinity. This technology opens up many opportunities for ITS. The fast focus change
Intertraffic World | Annual Showcase 2018
means that focus can be selected according to how close the vehicle is. It is possible to determine the distance of the vehicle by using a signal from a laser sensor or by analyzing one image and then setting the focus for the next.
Multiple image applications Liquid lenses are ideal for applications requiring multiple images as the focus can be moved so quickly between images. Where multiple lanes are being imaged, focus can be rapidly adjusted for each. In this way, it is possible to use a single camera for three lanes instead of three individual cameras, substantially reducing cost. Liquid lenses, such as those from Optotune, can change shape using a patented combination of optical fluids and a flexible polymer membrane. An electrically controlled outer diaphragm pushes down on the membrane to change the shape of the lens, making it possible to focus easily at different distances. Gardasoft’s GigE Vision-compliant TR-CL180 lens controller facilitates the fast, precise changing of focus.
Iris control For conventional lenses, the amount of light that reaches the camera sensor is controlled by opening and closing the iris. This can be performed automatically in response to
variations in light levels in the overall scene by using an auto-iris system. However, for ITS, the system has more specific aims, for example optimizing the brightness of a license plate. For this, the P-Iris arrangement is a preferred solution, combining stepper motor-driven adjustment of the iris with control of camera software settings such as gain and exposure time. Gardasoft can offer P-Iris control as an OEM module. By controlling the iris from the image processing software – which intelligently examines the image in terms of the desired information – much better control of the brightness can be achieved in the parts of the image that really matter. Specifically designed pulsed LED lighting provides ITS integrators with high luminous intensity, flexibility of installation and operation, with the added benefit of low cost of ownership. By pulsing the LED, the timing of the camera exposure can be exactly synchronized with the triggering of the light, and light intensity output can be readily adjusted. Driving the LED with a higher current for short pulses (overdriving) makes it possible to get more than 100% brightness from the light during those short pulses. All Gardasoft ITS LED controllers allow rapid adjustment of the frequency and power of light pulses, so multiple pulses of light of different intensities can be generated within
