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A vehicle's headlamp orientation and luminous and geometrical beam properties are a matter that is strictly ruled by the European Commission for transportation. To test the headlamps, a test system is usually manually aligned to the vehicle, and the human being has the definite opinion even on the beam-related measures. This paper presents a fully automatic system that exploits vision-based technology to extract the geometric parameters of the light profiles that are projected by vehicle headlamps in real time. The 3-D orientation of the longitudinal axis of the vehicle is recovered using stereoscopy. Furthermore, image analysis is used to automatically characterize the shadow-light border of a beam profile, as it would be perceived by an experienced human operator. A locally adaptive thresholding algorithm allows our system to automatically adjust to a wide range of light sources of different power. The alignment procedure and the beam characterization algorithm have been assessed through proper measuring apparatus that is capable of yielding accurate ground-truth data. In particular, the headlamp has been mounted on a special three-axis numerical control unit whose accuracy has been previously assessed, again using image analysis. Experimental results, which are carried out on a large number of different headlamps, show that our method is able to achieve accurate measurements in compliance with current regulations. Finally, it is worth remarking that our solution is fully automatic, and it just requires a simple setup procedure.
Instrumentation and Measurement, IEEE Transactions on (Volume:59 , Issue: 10 )
Date of Publication: Oct. 2010