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Practical Free-form RTI Acquisition with Local Spot Lights

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dc.contributor ["European Union (EU)" and "Horizon 2020"] Pintus, Ruggero Ciortan, Irina Giachetti, Andrea Gobbetti, Enrico 2016-09-12T13:57:30Z 2016-09-12T13:57:30Z 2016-10
dc.description.abstract We present an automated light calibration pipeline for free-form acquisition of shape and reflectance of objects using common off-the-shelf illuminators, such as LED lights, that can be placed arbitrarily close to the objects. We acquire multiple digital photographs of the studied object shot from a stationary camera. In each photograph, a light is freely positioned around the object in order to cover a wide variety of illumination directions. While common free-form acquisition approaches are based on the simplifying assumptions that the light sources are either sufficiently far from the object that all incoming light can be modeled using parallel rays, or that lights are local points emitting uniformly in space, we use the more realistic model of a scene lit by a moving local spot light with exponential fall-off depending on the cosine of the angle between the spot light optical axis and the illumination direction, raised to the power of the spot exponent. We recover all spot light parameters using a multipass numerical method. First, light positions are determined using standard methods used in photometric stereo approaches. Then, we exploit measures taken on a Lambertian reference planar object to recover the spot light exponent and the per-image spot light optical axis; we minimize the difference between the observed reflectance and the reflectance synthesized by using the near-field Lambertian equation. The optimization is performed in two passes, first generating a starting solution and then refining it using a Levenberg-Marquardt iterative minimizer. We demonstrate the effectiveness of the method based on an error analysis performed on analytical datasets, as well as on real-world experiments. en_US
dc.description.sponsorship Terms: "European Union (EU)" & "Horizon 2020" / Action: H2020-EU.3.6.3. - Reflective societies - cultural heritage and European identity / Acronym: Scan4Reco / Grant number: 665091 en_US
dc.language.iso en_US en_US
dc.publisher the Eurographics Association en_US
dc.relation info:eu-repo/grantAgreement/EC/H2020/665091/EU/Scan4Reco/Scan4Reco/
dc.rights the Eurographics Association
dc.rights.uri info:eu-repo/semantics/openAccess
dc.source Proc. Smart Tools and Apps for Graphics (STAG) 2016
dc.subject I.4.1 [Image processing and Computer Vision]: Digitization and Image Capture—Imaging Geometry en_US
dc.title Practical Free-form RTI Acquisition with Local Spot Lights en_US
dc.type info:eu-repo/semantics/article en_US
dc.type info:eu-repo/semantics/acceptedVersion

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