Unsupervised-learning-based calibration method in microscopic fringe projection profilometry.

Microscopic fringe projection profilometry (MFPP) technology is widely used in 3D measurement. The measurement precision performed by the MFPP system is closely related to the calibration accuracy. However, owing to the shallow depth of field, calibration in MFPP is frequently influenced by low-quality target images, which would generate inaccurate features and calibration parameter estimates. To alleviate the problem, this paper proposes an unsupervised-learning-based calibration robust to defocus and noise, which could effectively enhance the image quality and increase calibration accuracy. In this method, first, an unsupervised image deblurring network (UIDNet) is developed to recover a sharp target image from the deteriorated one. Free from capturing strictly paired images by a specific vision system or generating the dataset by simulation, the unsupervised deep learning framework can learn more accurate features from the multi-quality target dataset of convenient image acquisition. Second, multi-perceptual loss and Fourier frequency loss are introduced into the UIDNet to improve the training performance. Third, a robust calibration compensation strategy based on 2D discrete Fourier transform is also developed to evaluate the image quality and improve the detection accuracy of the reference feature centers for fine calibration. The relevant experiments demonstrate that the proposed calibration method can achieve superior performance in terms of calibration accuracy and measurement precision.