Tomislav Pribanić

A state of the art in structured light patterns for surface profilometry

Shape reconstruction using coded structured light is considered one of the most reliable techniques to recover object surfaces. Having a calibrated projector-camera pair, a light pattern is projected onto the scene and imaged by the camera. Correspondences between projected and recovered patterns are found and used to extract 3D surface information. This paper presents an up-to-date review and a new classification of the existing techniques. Some of these techniques have been implemented and compared, obtaining both qualitative and quantitative results. The advantages and drawbacks of the different patterns and their potentials are discussed.

Efficient multiple phase shift patterns for dense 3D acquisition in structured light scanning

Although phase shifts (PS) are frequently used to acquire colored surfaces of static objects, especially when acquisition time is not critical, the periodic nature of relative (wrapped) PS maps makes it necessary to deal with the issue of phase unwrapping. Consequently, multiple phase shifts (MPS) have been widely used as an alternative, but this usually involves a large number of different PS maps to unwrap an absolute (unique) phase. In this paper we propose a new MPS method to unwrap a phase and accurately perform the dense 3D acquisition of neutral and colored objects using only two PS maps. Accuracy is reported including a quantitative and qualitative evaluation of the results.

Calibration of 3D kinematic systems using orthogonality constraints

Processing images acquired by multi-camera systems is nowadays an effective and convenient way of performing 3D reconstruction. The basic output, i.e. the 3D location of points, can easily be further processed to also acquire information about additional kinematic data: velocity and acceleration. Hence, many such reconstruction systems are referred to as 3D kinematic systems and are very broadly used, among other tasks, for human motion analysis. A prerequisite for the actual reconstruction of the unknown points is the calibration of the multi-camera system. At present, many popular 3D kinematic systems offer so-called wand calibration, using a rigid bar with attached markers, which is from the end user’s point of view preferred over many traditional methods. During this work a brief criticism on different calibration strategies is given and typical calibration approaches for 3D kinematic systems are explained. In addition, alternative ways of calibration are proposed, especially for the initialization stage. More specifically, the proposed methods rely not only on the enforcement of known distances between markers, but also on the orthogonality of two or three rigidly linked wands. Besides, the proposed ideas utilize common present calibration tools and shorten the typical calibration procedure. The obtained reconstruction accuracy is quite comparable with that obtained by commercial 3D kinematic systems.

The choice of camera setup in 3D motion reconstruction systems

In this study the accuracy of 3D reconstruction systems using different camera setup in horizontal or vertical direction (plane) was investigated. Since it is critical that the object being filmed has to be visible by at least two cameras one is trying to keep cameras as parallel as possible to increase a common field of view. Also a camera positioned perpendicular to the area of interest assures better resolution in the horizontal and vertical directions (X-axis and Y-axis). On the other hand the depth resolution (Z-axis) suffers when cameras optical axes do not converge enough. Theoretically and also shown in practice angle of intersection from 60/spl deg/ to 120/spl deg/ is equally reliable. The convergent vertical camera set-up (one camera positioned above the other) is expected to encompass both requirements: depth of resolution and satisfactory large common field of view.

Absolute phase mapping for one-shot dense pattern projection

The use of one-shot pattern projection to obtain 3D dense reconstruction constitutes a promising field of research in structured light. Most of the related works presented in the literature are based on the projection of a fringe pattern to extract depth from phase deviation. However, the algorithms employed to unwrap the phase are computationally slow and can fail under certain slopes and occlusions in the object shape. In these lines, a color one-shot dense reconstruction using fringe pattern projection and wavelet decomposition is presented. Moreover, a novel phase unwrapping algorithm is proposed, providing a fast and reliable absolute phase map for depth reconstruction.

Single-Shot Dense 3D Reconstruction Using Self-Equalizing De Bruijn Sequence

Single-shot dense 3D reconstruction using colored structured light is a difficult problem due to the undesired effects of ambient lighting, object albedo, non-equal channel gains, and channel cross-talk. We propose a novel single-shot dense 3D reconstruction using colored structured light. Our method combines the self-equalizing De Bruijn sequence, scale-space analysis, and bandpass complex Hilbert filters to achieve insensitivity to ambient lighting, object albedo, and non-equal channel gains. The proposed method reconstructs about 85% of points compared to time-multiplexing structured light strategies and the decoding error in the recovered projector coordinate is less than one projector pixel for about 90% of reconstructed points.Single-shot dense 3D reconstruction using colored structured light is a difficult problem due to the undesired effects of ambient lighting, object albedo, non-equal channel gains, and channel cross-talk. We propose a novel single-shot dense 3D reconstruction using colored structured light. Our method combines the self-equalizing De Bruijn sequence, scale-space analysis, and bandpass complex Hilbert filters to achieve insensitivity to ambient lighting, object albedo, and non-equal channel gains. The proposed method reconstructs about 85% of points compared to time-multiplexing structured light strategies and the decoding error in the recovered projector coordinate is less than one projector pixel for about 90% of reconstructed points.

The Self-Equalizing De Bruijn Sequence for 3D Profilometry

Using color in 3D profilometry usually requires a tedious color calibration to mitigate the undesired effects of ambient lighting, object albedo, non-equal channel gains, and channel cross-talk. We propose a novel De Bruijn sequence for multi-channel structured light that removes the need for color calibration of a camera-projector pair. The proposed sequence has the following desirable properties: (1) it enables the extraction of ambient lighting, (2) it enables the cancellation of object albedo, and (3) it enables the equalization of channel gains.

An efficient surface registration using smartphone

Gathering 3D object information from the multiple spatial viewpoints typically brings up the problem of surface registration. More precisely, registration is used to fuse 3D data originally acquired from different viewpoints into a common coordinate system. This step often requires the use of relatively bulky and expensive robot arms (turntables) or presents a very challenging problem if constrained to software solutions. In this paper we present a novel surface registration method, motivated by an efficient and user-friendly implementation. Our system is inspired by the idea that three out of generally six registration parameters (degrees of freedom) can be provided in advance, at least to some degree of accuracy, by today’s smartphones. Experimental evaluations demonstrated the successful point cloud registrations of

Sequence-to-sequence alignment using a pendulum

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