In recent years, a lot of efforts have been devoted to the problem of depth estimation from lightfield images captured by standard plenoptic cameras. However, most of the metric depth estimation methods in the state-of-the-art leverage pixel disparity only. In this paper, we tackle the problem of focus-based metric depth estimation in standard plenoptic cameras. For this purpose we propose a closed-form model that relates the refocusing parameter with the focus distance of a plenoptic camera in order to allow for metric depth estimation. Based on the proposed model, we develop a calibration procedure that allows finding the parameters of the model. Using measurements of a time-of-flight sensor as ground-truth, experimental validation in a distance range of 0.2-1.6 m shows that focus-based depth estimation is feasible with a root-mean-squared error of less than 5 cm.
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