High dynamic range 3D shape measurement based on crosstalk characteristics of a color camera.

Fringe projection profilometry (FPP) has been widely used in many fields due to its fast speed, high accuracy and full-field characteristics. However, it is still a challenging problem to deal with high dynamic range (HDR) objects for traditional FPP, which utilizes a single exposure time or a single projection intensity. Overexposure will occur in areas with large reflectivity, which exceeds the maximum capturing capacity of camera sensors, resulting in the failure to obtain the accurate intensity, absolute phase and three-dimensional (3D) data. In this paper, a uniform blue image is projected to divide object surface into three areas with different reflectivity by using different intensity responses of RGB channels of color images. Crosstalk coefficient function is applied to obtain intensity of overexposed areas, and then the optimal exposure time of areas is calculated by the linear photometric response of the camera. Finally, three sets of blue fringe patterns with optimal exposure time are synthesized into the fused HDR images to calculate the absolute phase. Experimental results confirm that the proposed method can accurately measure HDR objects with large variation range of reflectivity.