In order to cover the high dynamic exposure range requirement of high reflective surface, a multiple-exposure adaptive selection algorithm of phase shifting 3D measurement is developed. At first, the camera response curve function is calibrated with the sequence images of different exposure times. The nonlinear curve function shows the relationship between the image intensity value and exposure amount. The relative irradiance value of all the image pixels is computed based on the linear relation between the exposure time and exposure amount. Both relative irradiance value cover the highest and lowest gray value of the fringe image is set the threshold. Then, the adaptive selection algorithm for exposure time is proposed based on the double threshold principle. At last, different exposure time node is selected adaptively. The sequences images with multi-exposure time are fused. In order to evaluate the performance of this method, some typical metal parts and blade with high range of reflectivity surfaces are used for 3D measurement and construction. The experiment results verify the feasibility of the proposed method.
This article presents an algorithm to avoid camera overexposure or underexposure by calculating and analyzing the camera response function. First, the range of intensity value and time is set to ensure that the intensity value of each image pixel is within the measurement range when the camera's exposure time is within the time range. Then, the reference image which has the maximum number of pixel intensity values within the intensity value range is selected. Third, the camera response function will be calculated based on the variation of the reference point intensity value with the exposure time. Finally, the whole exposure times will be recovered based on the computed response function, and used in the process of structured light measurement. The experimental results verify the performance and feasibility of the proposed method.
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