This paper presents an autofocusing method that can significantly expedite the autofocusing process in digital fringe projection. The proposed method employs an electrically tunable lens (ETL) to adjust the camera focal length. Initially, the proposed method roughly reconstructs the 3D shape of the measured object using three-step low-frequency phase-shifted fringe patterns. Then, the camera focal length is tuned to focus the measured object by analyzing the 3D data of the rough measurement. Finally, high-frequency phase-shifted fringe patterns are used to reconstruct a high-quality 3D point cloud. Experimental results demonstrated the success of the proposed method.
This paper presents an optimized capturing strategy for large depth-of-field (DOF) 3D microscopic structured-light imaging with the focus stacking technique. Different from the conventional focus stacking method that captures fringe images under a series of pre-defined focus settings, the proposed method automatically determines effective focus settings for the measured objects and only captures fringe images under these effective focus settings. Specifically, the proposed method first roughly measures the depths of objects using the focal sweep technique, then calculates the effective focus settings that locate the camera focal plane on the valid depths of the objects. Finally, the focus stacking technique is applied to reconstruct the 3D point cloud using the fringe images captured under the effective focus settings.
This paper presents a novel phase unwrapping algorithm via depth from focus method in microscopic fringe projection profilometry. The proposed method uses fringe contrast to estimate the rough depth information and determines the fringe orders by geometrical constraint relationships. As a result, it does not require extra patterns or images, enabling a higher 3D imaging speed. Experimental results demonstrate that the proposed method can successfully realize phase unwrapping in microscopic fringe projection profilometry.
This paper presents a calibration method for an extended-depth-of-field (EDOF) microscopic structured light system using a calibration target with black circles. The method first extends the DOF by the focal sweep technique to achieve a sufficient measurement range. Then, a computational framework is proposed to resolve the phase error problem caused by the black circles. Experimental results indicate that the proposed method works well in microscopic 3D shape measurement.
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