3d surface shape measurement using stereoscopic camera based structured light systems

Structured light measurement allows us to obtain three-dimensional surface shape of an object with high accuracy. Thus, it finds extensive applications in industrial applications. Moreover, by projecting digital fringe patterns to the measured object, structured light guarantees a flexible surface measurement. On the other hand, structured light also allows us to measure both specular objects and diffuser objects. For specular object measurement, deflectometry is introduced. Here, the fringe patterns are generated by a liquid crystal display (LCD). For diffuser object measurement, profilometry is introduced. In this technique, the fringe patterns are projected by a video projector. In this thesis, we firstly propose a stereoscopic phase measuring deflectometry (SPMD) system, which contains two cameras and a commercial LCD, to fulfill the specular object measurement. In particular, by introducing the stereoscopic camera, the undesired height-normal ambiguity is eliminated without moving any system component. Here, we propose a phase error minimization algorithm, which is fulfilled by searching the minimum phase difference between the corresponding pixels of the LCD and the camera, to simultaneously determine the surface normal and height. What is more, to accomplish an efficient phase minimization, we use a polynomial fitting method. Finally, two-dimensional Fourier integration is used to reconstruct the specular surface shape. Apart from the specular surface measurement with deflectometry, we also propose a stereoscopic fringe projection profilometry (SFPP) system to accomplish the diffuser object surface shape measurement. In particular, an SFPP system uses the same stereoscopic camera as in the deflectometry set-up, but it adopts a video projector to replace the LCD to project the fringe patterns. By introducing the stereoscopic camera, we avoid the complex video projector calibration, and thus, a great system flexibility is achieved. For surface reconstruction, geometric triangulation is implemented by performing a 2D sub-pixel interpolation, from which we enhance the surface reconstruction accuracy. The aforementioned two systems enable us only to measure the surface shape of either a specular or a diffuser object, but they show inadequacies to measure a specular-diffuser hybrid object. Under this scenario, we combine both systems to perform the specular-diffuser hybrid object measurement. Here, a stereoscopic deflectometry-profilometry hybrid (SDPH) system contains the stereoscopic camera, an LCD and a video projector. In this case, this hybrid system overcomes the inadequacy of single projection structured light systems, as it not only ensures to measure specular or diffuser object, but it also allows the measurement of specular-diffuser hybrid objects. Hence, the application of structured light measurement is further broadened. In summary, we demonstrate in this thesis three stereoscopic camera based structured light systems to perform three-dimensional surface shape measurement. These stereoscopic systems reveal great potential as they are able to measure the surface shapes of specular objects, diffuser objects and even specular-diffuser hybrid objects with high resolution. The proposed systems could be beneficial in various industrial applications, where an accurate surface shape measurement system with an easy implemented scheme is required.