Research On Imaging System Radiometric Calibration Used To Road Lighting Measurement

Road lighting measurement can not only evaluate the quality of road lighting quantitatively and qualitatively,but also provide data reference for the design of lighting device and the application of new light source,so as to improve the quality of road luminance.The traditional point-by-point measurement method is affected by problems such as traffic and the personal safety of surveyors.There are many measurement difficulties and waste of manpower and material resources.At the same time,due to the large dynamic range,large measurement space and high spatial sampling density of road lighting,the traditional lighting measurement method is difficult to fully meet these special requirements.Optical imaging measurement adopts the characteristics of multi-dimensional array spatial sampling of the imaging system detector,combines with the calibration method to establish the relationship between the image data output from the imaging system and the actual scene mapping,it can increase the dynamic range of measurement,expand the range of spatial sampling,and increase the density of spatial sampling.Optical imaging measurement method avoids many shortcomings of traditional multi-point measurement and becomes an effective and efficient method for illumination measurement.Calibration is the bridge between the measured value of the instrument and the real physical parameters reflected by it.It is a necessary link for the system to measure,and it is also the primary factor that determines the system’s measurement accuracy.Radiometric calibration is the mapping relation between the radiative energy of the input detector and the digital value of the sensor output.It can be expressed by the imaging system response function.The precision of imaging system restricts the development of imaging measurement and radiometric calibration has become an important part of imaging measurement research.This paper studies the radiation calibration of the imaging system for road lighting measurement,including two parts: the response non-uniformity caused by the inconsistent response characteristics between the detection elements and the mapping relationship between the system output and the input optical luminance.The first part is also known as the relative calibration between probe elements,and the second part is the absolute calibration.The non-uniformity of the system response affects the consistency to the measurement results of the large field of view scene.System photometric calibration affects the accuracy of system measurement.Because the night lighting scene has the characteristics of the large range of brightness ratio,for the high dynamic range scene imaging,a bright scene imaging range beyond imaging system,a dark scene imaging system is less than the scene information collected,lack of imaging system dynamic range limits the high dynamic range scene brightness imaging measurements,to extend the dynamic range imaging system to obtain high dynamic range image is imaging system was applied to a key link in the process of road illumination measurement.The relative and absolute calibration of an imaging system is an important process to determine its luminance measurement accuracy.Rapid and accurate measurement and evaluation of the complex luminance environment can reasonably design the road lighting system,it can reduce the traffic accident rate and is of great significance to the realization of green lighting and healthy lighting.