Efficient confidence measures for embedded stereo

The advent of embedded stereo cameras based on low-power and compact devices such as FPGAs (Field Programmable Gate Arrays) has enabled to effectively address several computer vision problems. However, being the depth data generated by stereo algorithms affected by errors, reliable strategies to detect wrong disparity assignments by means of confidence measures are desirable. Recent works proved that confidence measures are also a powerful cue to improve the overall accuracy of stereo. Most approaches aimed at predicting match reliability rely on cost volume analysis, an information seldom available as output of most embedded depth sensors. Therefore, in this paper we analyze and evaluate strategies compatible with the constraints of embedded stereo cameras. In particular, we focus our attention on methods to infer match reliability inside depth sensors based on highly constrained computing architectures such as FPGAs. We quantitatively assess, on Middlebury 2014 and KITTI 2015 datasets, the impact of different design strategies for 16 confidence measures from the literature, suited for implementation on such embedded systems. Our evaluation shows that, compared to the confidence measures typically deployed in this context and based on storing intermediate results, other approaches yield much more accurate predictions with negligible computing requirements and memory footprint. This enables for their implementation even on highly constrained architectures.