The measuring technique combining phase-shifting algorithm and Gray-code light has been widely used in threedimensional (3D) shape measurement for static scenes owing to its high robustness and anti-noise ability. However, it is challenging for this method to realize a high-speed shape measurement using fewer patterns. Because of the object motion and the defocus of the projector, phase unwrapping errors occur easily on the boundaries of adjacent Gray-code words. In existing methods, median filtering or extra patterns projecting were used to overcome this challenge. In this paper, two robust Gray-code coding strategies have been proposed for the same purpose. By recoding the traditional Gray codes in temporal and spatial domains respectively, cyclic complementary Gray-code (CCGC) patterns and shifting Gray-code (SGC) patterns are designed. Both of these two coding strategies can obtain two sets of decoding words whose boundaries are stagger for one wrapped phase. To avoid using the decoding words on the edge, different decoding codes are used depending on the range of phase value. So the robust and simple phase unwrapping can be achieved without projecting extra patterns. High-quality 3D results of multiple randomly moving objects with sharp edges verified the proposed methods’ feasibility and validity
Phase-to-height mapping is indispensable part of three-dimensional (3D) shape measurement system based on phase analysis, which guarantees the accuracy of 3D reconstruction. In this paper, a real time 3D shape reconstruction method based on dual-frequency composite grating projection and phase-height lookup table is proposed. In this method, a reference plane is moved with a known interval along the measurement depth direction to establish a mapping lookup table between the wrapped phase of dual-frequency composite grating and the corresponding spatial height pixel by pixel respectively. The actual experimental results show that the reconstruction accuracy of this method is better than that of the traditional phase-to-height quadratic fitting method. Finally, combining the high performance parallel computation of GPU, the real time 3D shape reconstruction with the speed of 60 fps and the resolution of 1152*800 pixels is realized.
In the existing intensity-ratio measuring methods, unwrapping the intensity ratio may be erroneous or even fail when measuring complex and isolated objects. This paper presents an improved three-dimensional (3-D) profile measuring method based on intensity-ratio measurement. Two shifting triangular patterns are projected to generate a triangular intensity-ratio distribution, and a Ronchi grating is projected to correctly divide the triangular intensity-ratio regions. Then, an absolute intensity ratio is retrieved point-by-point with the periodic label of the projected Ronchi grating. Finally, the intensity-ratio-to-height mapping algorithm is used to reconstruct the 3-D surface shape. The experimental results have demonstrated the feasibility and validity of the proposed method in restoring 3-D surface shape of the complex and isolated objects.
Three-dimensional (3-D) shape measurement technology based on structured light has become one hot research field inspired by the increasing requirements. Many methods have been implemented and applied in the industry applications, but most of their equipments are large and complex, cannot be portable. Meanwhile, the popularity of the smart mobile terminals, such as smart phones, provides a platform for the miniaturization and portability of this technology. The measurement system based on phase-shift algorithm and Gray-code pattern under the Android platform on a mobile phone is mainly studied and developed, and it has been encapsulated into a mobile phone application in order to reconstruct 3-D shape data in the employed smart phone easily and quickly. The experimental results of two measured object are given in this paper and demonstrate the application we developed in the mobile platform is effective.