However, the use of this system still involves difficulties when dealing with nondiffuse (non-Lambertian) surfaces because the optical signal cannot be properly retrieved. The measured point cloud of the object can be further compared with the computer aided design (CAD) model to evaluate the manufacturing quality. Finally, the 3D coordinates of the object surface can be calculated from the absolute phase map using a phase-to-height mapping based on a calibration performed earlier over the measurement volume of interest. Then, from the captured images, a specially designed algorithm, such as a phase-shifting algorithm, is employed to obtain the absolute phase map, which can be used for determining correspondences between the camera and the projector in a structured light system. The reflected pattern has the height information of the object embedded in its phase distribution.

The camera captures images of the reflected pattern deformed by the object surface from another direction. Typically, a structured light measurement system consists of a camera and a projector that projects a sequence of coded patterns onto object surfaces. Among these, the structured light method is one of the most widely used 3D shape measurement techniques owing to the advantages of full-field inspection, high resolution, and accuracy that it offers. These methods include time-of-flight, stereovision, photogrammetry, laser range scanning, and structured light methods. In contrast, the optical methods have an ability to provide a high-speed 3D inspection of objects in a noncontact manner. However, CMM is relatively slow and only measures a limited number of points in an objectвЂ™s surface. The surface contact measurement system, such as mechanical probe-based coordinate measuring machine (CMM), has been used in the industry for many years and can measure geometric shape with high accuracy (usually more accurate than current noncontact systems).

These techniques cover a wide range from microscale objects, such as interferometry and confocal techniques, to several meter-sized objects, such as time-of-flight technique, and generally can be classified into two categories: surface contact and surface noncontact. The recent release of Microsoft Kinect has enabled 3D technology to penetrate into our daily lives, and the combination of 3D printing technology with 3D shape measurement techniques could generate additional excitement across disciplines. A significant number of techniques for acquiring 3D shapes have been proposed, leading to a wide range of applications, such as range sensing, industrial inspection of manufactured parts, reverse engineering (digitization of complex, free-form surfaces), object recognition, entertainment, 3D map building, biometrics, and documentation of cultural artifacts.

Three-dimensional (3D) shape measurement is an important topic that has been investigated to a large extent. We present a survey of recent HDR techniques for the digitization of shiny surfaces and classify and discuss the advantages and drawbacks of different techniques with respect to each other. Some reviews summarize the different 3D imaging techniques however, no comprehensive review exists that provides an insight into high-dynamic range (HDR) 3D shape measurement techniques used for shiny surfaces. Therefore, various techniques have been investigated to solve this problem over the last few years. There are a large number of measurement demands for metallic workpieces with shiny surfaces in industrial applications however, such shiny surfaces cannot be directly measured using the conventional structured light method. In the last decade, a significant number of techniques for three-dimensional (3D) shape measurement have been proposed.

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