Depth recovery and parameter analysis using single-lens prism based stereovision system

Abstract

This thesis aims to study the depth recovery and parameter analysis of a single-lens bi-prism based stereovision system. The 2D image is captured by this system and can be split into two sub-images on the camera image plane, which are assumed to be captured by two virtual cameras simultaneously. A point in the 3D space would appear in different locations in each of the image planes, and the differences in positions between them are called the disparities. The depth information of the point can then be recovered by using the system setup parameters and the disparities. This system offers several advantages over the conventional system which uses two cameras, such as compactness, lower costs and ease in operation. In this research, the concept and formation of the virtual cameras are also introduced and parameters of the system are studied in detailed to improve the accuracy of the depth recovery. A geometry-based approach has been proposed to calibrate the two virtual cameras generated by the system. The projection transformation matrices or the extrinsic parameters of the virtual cameras are computed by a unique geometrical ray sketching approach. Based on the calibrated virtual cameras, a virtual epipolar line approach is presented to solve the correspondence problem of the system. A specially designed experimental setup, with high precision stage was fabricated to conduct experiments. The results show that the proposed approach is effective and robust. By comparing the results of the proposed geometry-based approach to the results of conventional stereovision technique, the former approach produces better results. Furthermore, the geometrical approach is used to predict the type of field of view (FOV) produced given a bi-prism angle. The two main types of FOV generated by this system are divergent FOV and convergent FOV. By using the ray sketching approach, the geometry of each type of FOV can be theoretically estimated. Then, the effect of translation of bi-prism in the z- and x?-axes on the system?s FOV is determined using geometrical analysis. Experiments are conducted to verify the above predictions. While there are some degree of quantitative error between experimental results and theory, the general theoretical trends are largely supported by the results. Finally, the parameter/error analysis of the single-lens bi-prism stereovision system in terms of the system parameters is studied in detailed. Theoretical equations are derived to estimate the error and the trend of error when the object distances increase. The relative depth error which is essential to design the system appropriately for practical usage is then formulated. Based on the findings, the possibility of manipulating the system parameters, named as variable parameter is then presented in order to reduce or maintain the error of the system for long range applications. To summarize, the main contribution of this thesis is the development of a novel stereo vision technique. All the efforts are made to recover the depth of a 3D scene using the single-lens bi-prism based stereovision system and to improve the accuracy of the results.