A grid-point detection method based on U-net for a structured light system

Accurate detection of the feature points of the projected pattern plays an extremely important role in one-shot 3D reconstruction systems, especially for the ones using a grid pattern. To solve this problem, this paper proposes a grid-point detection method based on U-net. A specific dataset is designed that includes the images captured with the two-shot imaging method and the ones acquired with the one-shot imaging method. Among them, the images in the first group after labeled as the ground truth images and the images captured at the same pose with the one-shot method are cut into small patches with the size of 64x64 pixels then feed to the training set. The remaining of the images in the second group is the test set. The experimental results show that our method can achieve a better detecting performance with higher accuracy in comparison with the previous methods.Comment: http://airccse.org/csit/V10N16.htm

Acquisition of 3D shapes of moving objects using fringe projection profilometry

Three-dimensional (3D) shape measurement for object surface reconstruction has potential applications in many areas, such as security, manufacturing and entertainment. As an effective non-contact technique for 3D shape measurements, fringe projection profilometry (FPP) has attracted significant research interests because of its high measurement speed, high measurement accuracy and ease to implement. Conventional FPP analysis approaches are applicable to the calculation of phase differences for static objects. However, 3D shape measurement for dynamic objects remains a challenging task, although they are highly demanded in many applications. The study of this thesis work aims to enhance the measurement accuracy of the FPP techniques for the 3D shape of objects subject to movement in the 3D space. The 3D movement of objects changes not only the position of the object but also the height information with respect to the measurement system, resulting in motion-induced errors with the use of existing FPP technology. The thesis presents the work conducted for solutions of this challenging problem

Single-Shot Direct Block Address Encoding for Learning Screen Geometry

3D surface reconstruction has many applications in different domains such as projection mapping, virtual reality, robot navigation, human computer interaction and manufacturing inspection, to name a few. Among different methods of 3D reconstruction, structured light is widely used as it is comparatively cheap and accessible and solves the main problem of traditional stereo vision systems which is finding accurate pixel correspondences between two or multiple views. Structured light techniques can be most fundamentally categorized in terms of the number of projected images over time, whether a single image (single-shot) or multiple images (multi-shot). Multi-shot structured light methods take advantage of multiple images that are projected sequentially over time, allowing simple encoding / decoding of projector pixel addresses. In contrast, single-shot structured light is preferred in contexts of dynamically moving cameras, projectors or surfaces, and in scenarios where short projection time is important. In this thesis, a new framework for designing single-shot structured light images using tag embedding, called Direct Block Address Encoding, is presented which, unlike previous methods, results in efficient encoding, decoding and 3D reconstruction. Also, error detection and correction mechanisms are designed to detect pixel codewords with errors and find their correspondences in the projector image. In addition, the relationship between different design parameters (alphabet size, encoding Scheme, tag size, block size) are derived to cover projectors with different resolutions. Experimental results demonstrate that the proposed scheme is capable of obtaining projector-camera pixel correspondences at higher speed in comparison with previous tag embedding methods, allowing for learning screen geometry from a single shot with high resolution projectors and dynamic cameras and projectors. The proposed Direct Block Address Encoding scheme offers 2-3 times speed up for 3D reconstruction and 5-6 times speed up for encoding/decoding stages due to not requiring a look-up table and/or an exhaustive search, something not achieved with other methods

Single-pixel digital holography with phase-encoded illumination

We demonstrate imaging of complex amplitude objects through digital holography with phase-structured illumination and bucket detection. The object is sampled with a set of micro-structured phase patterns implemented onto a liquid-crystal spatial light modulator while a bucket detector sequentially records the irradiance fluctuations corresponding to the interference between object and reference beams. Our reconstruction algorithm retrieves the unknown phase information from the full set of photocurrent measurements. Interestingly, the sampling functions can be codified onto the reference beam, so they can be nonlocal with respect to the object. Finally, we show that the system is well-fitted for transmission of the object information through scattering media