The Improvement Of High-speed 3D Surface Measurement Using Color-encoded Stripe

As the development of digital technology, optical 3D measurement plays an increasingly important role in enormous fields including virtual reality, automatic industrial detection, biomedical, cultural reproduction, art sculptures and face recognition, etc. Recently, Structured-light 3D shape measurement, with the features of non-contact, high sensitivity and high accuracy, has been developing rapidly and researching widely. How to measure the shape of the objects at high speed is one of the research focuses, the 3D shapes have to be required rapidly, processing quickly and displayed in real time. Although the high-speed 3D shape measurement systems have been developed gradually, there are many aspects which need to be improved.In this paper, a color-encoded digital fringe projection technique is introduced for 3D shape measurement. In this technique, a color fringe pattern whose RGB components comprise three fringe patterns in different way of coding is projected to the objects. The deformed fringe image which is captured by the camera is separated into its RGB components. Therefore, it just need only one color image for construction and the measurement speed can be increased greatly. The key point of this technique is how to build the relationship and modify RGB components. In view of the developing trend, a new process method is proposed to solve the difficulty, and the improvements of 3D shape measurement are as follow:(1) In Fourier transform profilometry, there exists a problem of frequency aliasing. So as to depress the effect of zero frequency, the bi-color sinusoidal patterns are adopted. A novel intensity-modulated method is proposed to eliminate the zero frequency component, which can improve the measuring precision and range. Compared to the traditional phase shift method to eliminate the zero frequency component, this method has a significant advantage at speed and proven to be suitable for real-time measurement of three-dimensional objects.(2) In phase measurement profilometry, use of color-encoded fringe pattern raise two major problems, color coupling and color imbalance. Due to these two factors, the RGB components after separation cannot be directly used for phase demodulation. Therefore, the intensity modulated function is used to modify the average intensity and the ratio of contrast intensity and make them balance. The feasibility of the algorithm is validated by both theoretical simulation and experiment performance and this method is suitable for high-speed 3D shape measurement.(3) Using the calibration functions of the computer vision library OpenCV, the calibration flow-path of the camera system is designed. It can calculate the camera intrinsic parameters and distortion parameters quickly and correct the image distortion effectively.(4) Aim at the non-sinusoidal of the projection system, a new solution idea is proposed. Before correcting the Gamma value, it should exclude the impact of other factors mainly through determining the arguments of average intensity and contrast intensity. The best Gamma value is automatically determined through calculating the spectral distribution which is obtained by Fourier transform.