Browsing by Subject "photogrammetry"

Now showing 1 - 4 of 4
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    Image-Based Relighting of 3D Objects from Flash Photographs
    (2019-05) Tetzlaff, Michael
    Photography is a remarkable technology that allows us to capture and reproduce the appearance of the real world. Although photographs are two-dimensional and static, their capabilities have been extended into higher dimensions through the development of techniques like photogrammetry, image-based rendering, and image-based relighting. Such prior work, however, has struggled to support dynamic illumination of the subject while still representing specular reflections accurately, especially for subjects that exhibit heterogeneity in their appearance. The most successful results in this direction usually require thousands of images. This dissertation introduces a new paradigm for image-based relighting of 3D objects that requires no more than a few hundred flash photographs. The flash lighting configuration is conveniently found on most commodity cameras. After being processed using traditional photogrammetry, the flash images serve as a collection of virtual light sources in a relighting system, through the power of Cook-Torrance microfacet theory. This approach produces new images of 3D objects that effectively retain the photographic accuracy of the subject's color appearance from the original flash photos. The same flash images can also be used to estimate reflectance parameters that improve the accuracy of the relighting technique. This rendering method can even be used to emulate lighting conditions -- both outdoor and indoor -- that are very different than flash. This work proceeds to show how the intensities of point light sources derived from the collection of flash images can be chosen to effectively emulate the intended environment. Although similar results have been previously achieved using thousands of images, the method shown here can be effective with a few hundred images or less. However, this reduction is not without limitation; a shinier object requires more photographs to avoid discontinuity between the intended environment and its reflection. To address this one limitation, this work ultimately develops a fidelity metric for assessing whether reflections of individual light sources are likely to be discernible when the object is relit. This metric is a heuristic solution which estimates the magnitude of this issue by quantifying the degree of overlap in specular reflections between similar images in the dataset. It is believed to be the first work which assesses the fidelity of how highlights are depicted when an object is relit using a limited number of views. This solution is shown to be generally effective and serves as a foundation which can be built upon by future metrics.
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    A Simple Photogrammetry Rig for the Reliable Creation of 3D Artifact Models in the Field: Lithic Examples from the Early Upper Paleolithic Sequence of Les Cottés (France)
    (2015-06-01) Porter, Samantha T; Roussel, Morgan; Soressi, Marie; port0228@umn.edu; Porter, Samantha T
    3D scanning is becoming an increasingly utilized tool in archaeology. In comparison with other methods of 3D registration close-range photogrammetry has the benefits of being relatively inexpensive, mobile, and extremely adaptable for use in field conditions. Here, 3D models of lithic cores from the Châtelperronian, Protoaurignacian, and Early Aurignacian levels of the site of Les Cottés (France) are presented as examples of the quality of model that can be produced using photographs taken with a simple and inexpensive photogrammetry rig.
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    Three Dimensional Models and Two Dimensional Cross Sections of Châtelperronian and Protoaurignacian Lithic Cores from the Sites of Les Cottés and Roc de Combe
    (2018-05-29) Porter, Samantha T; Roussel, Morgan; Soressi, Marie; stporter@umn.edu; Porter, Samantha T
    These data were generated as part of a study investigating the use of quantitative methods on three dimensional models of lithic artifacts. The majority of the data set is comprised of 3D scans of Châtelperronian and Protoaurignacian cores from the site of Les Cottés (France), which were generated using photogrammetry. Although cores from the site of Roc de Combe were also scanned for the associated study, we are not able to make them available here due to rights restrictions. The second part of the data set includes two dimensional representations of cross sections, which were from the 3D artifact models. These were used in two analyses, which are described in the associated publication in JCAA (see citation below).
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    Three-Dimensional Models of Experimentally-Produced Lithic Artifacts Created using Expedient and Refined Photogrammetry Protocols
    (2016-05-16) Magnani, Matthew; Douglass, Matthew; Porter, Samantha T; port0228@umn.edu; Porter, Samantha T
    The data set consists of three-dimensional (3D) models of experimentally produced lithic artifacts created using both expedient and refined photogrammetric setups and processing protocols. Source images for all models were captured using a 12.1 megapixel Canon PowerShot SX260 HS compact digital camera. In our expedient protocol, objects were placed on a wire stand. The photographer moved around the object, and captured photos using Auto mode. In our refined protocol, objects were placed on a rotating turntable under controlled lighting conditions. The camera was placed on a tripod. Shutter speed, f-stop, and ISO were set manually. This refined protocol is described in Porter, S. T., Roussel, M., & Soressi, M. (2016). A Simple Photogrammetry Rig for the Reliable Creation of 3D Artifact Models in the Field Lithic Examples from the Early Upper Paleolithic Sequence of Les Cottés (France). Advances in Archaeological Practice, 4(1), 71-86. The associated paper discusses the relative fidelity of the models produced using these different workflows. Models may also be viewed online (in browser) at: https://sketchfab.com/unlarchaeology/collections/magnani-et-al-2016.