Abstract
Due to the limited depth-of-field (DOF) of conventional digital cameras, only the objects within a certain distance range from the camera are in focus. Objects outside the DOF are observed with different amounts of defocus depending on their position. Focus sampling consists of capturing different images of the same scene by changing the focus configuration of the camera in order to alternately bring objects at different depths into focus. Focus sampling is an important part of different focus-related applications such as autofocus, focus stacking and depth estimation. This work proposes a calibration procedure for modeling the depth-of-field of conventional cameras in order to perform an efficient focus sampling. The method is simple in terms of repeatability and can be easily implemented in different imaging devices. Experimental tests are presented in order to illustrate the effectiveness of the proposed approach in autofocus. Results demonstrate that a significant reduction in the number of frames required to capture during autofocusing can be achieved by means of the proposed methodology.
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Notes
In a compound lens system, \(f\) corresponds to the effective focal length of the system.
In the perspective projection model, this product is also referred to as focal length. It should not be confused with the lens focal length, which describes the power of the optics and determines the behavior of focus. In this paper, the term focal length refers to the lens focal length.
The line spread function is the analytical response of an optical system to a step edge.
This distance is often referred to as hyperfocal distance.
Hill-climbing and rule-based search were not included due to their dependence on different heuristic parameters. These parameters depend on the sampling step and, hence, would not allow an objective comparison.
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Communicated by M. Hebert.
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Pertuz, S., Garcia, M.A. & Puig, D. Efficient Focus Sampling Through Depth-of-Field Calibration. Int J Comput Vis 112, 342–353 (2015). https://doi.org/10.1007/s11263-014-0770-0
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DOI: https://doi.org/10.1007/s11263-014-0770-0