Multi-Camera Three-Dimensional Measurement System Using an Image Stitching Method Based on Flexible Calibration Target Positioning

A multi-camera three-dimensional (3D) measurement system using an image stitching method based on flexible calibration target positioning is proposed. In order to expand the measuring range of the 3D shape measurement system, a laser projector is used to project large fringe images, followed with distributed multiple cameras to grab images of each field of view (FOV). The first step of calibration process is to establish the mapping relationship from the image coordinates and absolute phase to the world coordinates by using the reference camera with a small planar calibration target. Then, with the FOV of adjacent cameras partially overlapping, the flexible calibration target positioning is applied to calibrate mapping relationships of the image coordinates from adjacent cameras. After that, the image coordinates of all the other cameras arc converted to the image coordinates of the reference camera by the new image stitching method. Finally, the reference camera coordinates arc transformed to the world coordinates. The experimental results show that the accuracy of this method is slightly lower than the local measuring method with a single camera. However, the accuracy loss is not so severe, meeting the requirement for industrial on-line measurement. This method does not require expensive auxiliary measuring instruments or manufacturing large calibration targets with high precision, thus offering a low-cost and easy alternative for multi-camera 3D shape measurement systems.