Camera-independent saturation avoidance in measuring high-reflectivity-variation surfaces using pixel-wise composed images from projected patterns of different maximum gray level

This paper presents a camera-independent method of avoiding image saturation in three-dimensional (3D) shape measurement of objects with a high range of reflectivity variation across the surface. Multiple sets of phased-shifted sinusoidal fringe patterns of different maximum gray level are first projected onto the object surface while images are captured of the fringe patterns. Then composite images are constructed pixel-by-pixel, by using at each pixel, only the highest intensity without saturation across a set of phase-shifted images. The composite images are then used in phase map and surface generation. Measurements of a surface with large range of reflectivity and high luminance variation across the surface demonstrated measurement accuracy improvements of 0.20 mm to 0.32 mm, using the composite-images based on multiple maximum projected gray levels, compared to measurement with the best single uniform maximum gray level across the projected patterns. This saturation avoidance method can be performed automatically independent of any camera-lens hardware and would permit a wide range of measurement applications in uncontrolled environments. (C) 2014 Elsevier B.V. All rights reserved.