Calibration of light-match screen for detection of photometric characteristics of vehicle headlamp using photogrammetry

According to the feature of matrix-CCD-camera based on photogrammetric system of photometric characteristics of vehicle headlamp, an approach to calibrate light-match screen for detection of photometric characteristics of vehicle headlamp combined with photogrammetry and image processing technology is firstly proposed, in which the photogrammetric system is directly used to capture images of the light-match screen against which a straight-line target is rested at different illuminance-detecting positions. During the image processing, these straight-line targets are extracted from these images using image subtraction and image binarization, and thinned as straight lines using thinning algorithm. Finally, these single straight-line images are merged as a illuminance-detecting position target image using the “paste” and “cut” algorithm proposed in the paper. The calibration approach is used not only to implement the maintenance of characteristics of homogeneous reflectance of light-match screen, but also to implement the location of illuminance-detecting positions on light-match screen with the corresponding imaging coordinates on the illuminance-detecting position target image during the photogrammetry of photometric characteristics of vehicle headlamp, and the calibration approach is advantageous to implementation of simultaneous photogrammetry of illuminance at each position on light-match screen. The experimental results show that the photogrammetry-based calibrating system meets the detection requirements of photometric characteristics of vehicle headlamp with the calibration accuracy of 93.53%.