FPGA synthesis of an stereo image matching architecture for autonomous mobile robots

This paper describes a hardware proposal to speed up the process of image matching in stereo vision systems like those employed by autonomous mobile robots. This proposal combines a classical window-based matching approach with a previous stage, where key points are selected from each image of the stereo pair. In this first step the key point extraction method is based on the SIFT algorithm. Thus, in the second step, the window-based matching is only applied to the set of selected key points, instead of to the whole images. For images with a 1% of key points, this method speeds up the matching four orders of magnitude. This proposal is, on the one hand, a better parallelizable architecture than the original SIFT, and on the other, a faster technique than a full image windows matching approach. The architecture has been implemented on a lower power Virtex 6 FPGA and it achieves a image matching speed above 30 fps.This work has been funded by Spanish government project TEC2015-66878-C3-2-R (MINECO/FEDER, UE)

Wide baseline stereo matching based on scale invariant feature transformation with hybrid geometric constraints

Wide baseline stereo matching is a challenging task because of the presence of significant geometric deformations and illumination changes within the images. Based on the scale invariant feature transformation (SIFT) algorithm, this study proposes a new hybrid matching scheme that uses both the feature‐based and the area‐based methods to find reliable matches from sparse to dense under different geometric constraints. Firstly, the authors propose a SIFT‐based robust weighted least squares matching (LSM) method modelled by a two‐dimensional (2D) projective transformation to establish the initial correspondences and their local homographies. In this method, a normalised cross correlation metric modified with an adaptive scale and an orientation of the SIFT features (SIFT‐NCC) is proposed to find a good initial alignment for the SIFT‐LSM. Secondly, a robust matching propagation using the SIFT‐NCC starts from the initial matches under an epipolar geometry and the local homography constraints; geometrical consistency checking is used simultaneously to identify the false matches. Thirdly, they use an improved, feature‐based SIFT matching method to find the correspondences from the points that are not coplanar in the 3D space under an epipolar constraint only. A bidirectional selection strategy is used to remove the error matches