Strobed IR Illumination for Image Quality Improvement in Surveillance Cameras

Abstract: Infrared (IR) illumination is commonly found in a surveillance camera to improve night-time recording quality. However, the limited available power from Power over Ethernet (PoE) connection in networkenabled cameras restricts the possibilities of increasing image quality by allocating more power to the illumination system.The thesis explored an alternative way to improve the image quality by using strobed IR illumination. Different strobing methods will be discussed in relation to the rolling shutter timing commonly used in CMOS sensors. The method that benefits the evaluation scenario the most was implemented in a prototype which is based on a commercialized fixed-box camera from Axis. The prototype demonstrated how the synchronization of the sensor and the strobing illumination system can be achieved.License plate recognition (LPR) in a dark highway was chosen as the evaluation scenario and an analysis on the car movements was done in a pursue of creating an indoor test. The indoor test provided a controlled environment while the outdoor test exposed the prototype to real-life conditions. The test results show that with strobed IR, the output image experienced brightness improvement and reduction in rolling shutter artifact, compared to constant IR. The theoretical calculation also proved that these improvement does not compromise the average power consumption and eye-safety level of the illumination system.