Grid point extraction exploiting point symmetry in a pseudo-random color pattern

Structured light system together with the use of pseudo-randomly coded pattern in the projection is an effective solution for 3D reconstruction; it requires only a single image capture to operate. In this article, a 2D pseudo-random pattern consisting of rhombic color elements is proposed, and the grid-points between the pattern elements as opposed to the centroids of the elements are adopted as the feature points. Two possible types of grid-point are described, and a scheme that allows each grid-point to be uniquely distinguished by a codeword and the grid-point type it belongs to is described. We also present a grid-point detector that is based upon a certain symmetry the grid-points of rhombic pattern own — the 2-fold rotation symmetry — which is largely preserved under pattern projection, reflection, perspective distortion, image noise, and image blur.