Real-time surfaces reconstruction using coded structured light
ICube, Region Alsace, Karl Storz Company, IRCAD.
In this project, the robust matching technique based on coded structured lighting (SL) is addressed to achieve real-time surface reconstructions, like for a stero-like vision system.
To that purpose, most existing approaches involve color or grey levels coding (Figure 1) but they are well-known to be sensitive to spectral properties and texture of the viewed surfaces.
Therefore, the overall robustness of the proposed technique comes first from the geometrical features used in cunjonction with the SL neighbourhood scheme to carry out pattern coding. Second, a desired minimum Hamming distance between features' codewords drives the pattern design. This is suited for autonomous navigation in unknown environment as this parameter enables impressive codewords correction capabilities during the decoding stage and a new pattern can be produced in (video) real-time.
Furthermore, we take advantage of the known epipolar geometry (Figure 2) by including projective invariants between corresponding epipolar lines directly in the pattern components. Thus, the final pattern displays relocated and reoriented (cuneiform) features along the epipolar lines (Figure 3).
This grouping also contribute to reduce the search space more and results in a significant less constrained coding. This technique provides very big patterns (100 x 150) with high correction capabilities (Hmin > 1). For practical considerations, each numerical codeword symbol is associated to a unique visual feature embedding the local orientation of the pattern, which is helpful for the neighbourhood retrieval during the decoding process. Finally, we show how this coding and this non-grid based pattern offer efficient and fast correction of mislabeled features due to blurring, spectral harmful effects and surfaces discontinuities prior to the 3-D reconstruction of real scenes (Figures 4 and 5).
In vivo experiments at IRCAD France
Together with the endoscopic device, in vivo real-time reconstructions (in mini-invasive surgical conditions) have been performed in the surgery room of IRCAD, Strasbourg. Renderings are displayed on Figures 6-a and 6-b.
This allows to assess both the efficiency of the proposed pattern design, the decoding process with the 3-D laparoscope setup realized in the lab.
Perfect map theory (PSM),
Epipolar lines invariance,
Chadi Albitar (2005-2009)
Xavier Maurice (2008-2012)
Professeur, Télécom Physique Strasbourg