Focusing on Out-Of-Focus

Abstract

Acquiring photographs as input for an image-based modelling pipeline is less trivial than often assumed. Photographs should be correctly exposed, cover the subject sufficiently from all possible angles, have the required spatial resolution, be devoid of any motion blur, exhibit accurate focus and feature an adequate depth of field. The last four characteristics all determine the sharpness'' of an image and the photogrammetric, computer vision and hybrid photogrammetric computer vision communities all assume that the object to be modelled is depicted acceptably’’ sharp throughout the whole image collection. Although none of these three fields has ever properly quantified ``acceptably sharp’’, it is more or less standard practice to mask those image portions that appear to be unsharp due to the limited depth of field around the plane of focus (whether this means blurry object parts or completely out-of-focus backgrounds). This paper will assess how well- or ill-suited defocus estimating algorithms are for automatically masking a series of photographs, since this could speed up modelling pipelines with many hundreds or thousands of photographs. To that end, the paper uses five different real-world datasets and compares the output of three state-of-the-art edge-based defocus estimators. Afterwards, critical comments and plans for the future finalise this paper. Please cite as: Verhoeven, G., 2018. Focusing on out-of-focus. ISPRS Technical Commission II Symposium 2018 textquotedblTowards Photogrammetry 2020textquotedbl, 07 June 2018, Riva del Garda, Italy. DOI: 10.5281/zenodo.1285964

Geert Julien Joanna Verhoeven
Geert Julien Joanna Verhoeven
Vice Director, Senior Researcher