The mapping relationship between the charge-coupled device (CCD) of a camera and the digital micro-mirror device (DMD) of a projector, together with the algorithm to estimate the parameters of the projector, determines the accuracy of projector calibration. In this paper, a new method is presented to achieve sub-pixel-level mapping between the camera and projector images. Instead of directly mapping the circle centers from the CCD to the DMD, which is pixel-precision-based, a set of pixels on the circle edge are extracted on the CCD and mapped onto the DMD. The locations of the circle centers are extracted on the DMD by the least-squares fitting technique, thus achieving sub-pixel precision. Compared with existing approaches based on the direct mapping of the circle centers on the camera image to the projector image, the proposed method is characterized by higher accuracy in mapping the points and thus the projector calibration. The experimental results are presented to show the effectiveness of the proposed method in the improvement of the accuracy of the projector calibration.

The accuracy performance of fringe projection profilometry (FPP) depends on accurate phase-to-height (PTH) mapping and system calibration. The existing PTH mapping is derived based on the condition that the plane formed by axes of camera and projector is perpendicular to the reference plane, and measurement error occurs when the condition is not met. In this paper, a new geometric model for FPP is presented to lift the condition, resulting in a new PTH mapping relationship. The new model involves seven parameters, and a new system calibration method is proposed to determine their values. Experiments are conducted to verify the performance of the proposed technique, showing a noticeable improvement in the accuracy of 3D shape measurement. Disciplines Engineering | Science and Technology Studies