Abstract
Abstract. Software tools for photogrametric and multi-view stereo reconstruction are nowadays of generalized use in the digitization of architectural cultural heritage. Together with laser scanners, these are well established methods to digitize the three-dimensional geometric properties of real objects. However, the acquired photographic colour mapping of the resulting point clouds or the textured mesh cannot differentiate the proper surface appearance from the influence of the particular illumination present at the moment of the digitization. Acquisition of the actual surface appearance, separated from the existing illumination, is still a challenge for any kind of cultural heritage item, but very specially for architectural elements. Methods based on systematic sampling with commuting light patterns in a laboratory set-up are not suitable. Immovable and outdoor items are normally limited to the existing and uncontrolled natural illumination. This paper demonstrates a practical methodology for appearance acquisition, previously introduced in (Martos and Ruiz, 2013), applied here specifically for the production of re-illuminable architectural orthoimages. It is suitable for outdoor environments, where the illumination is variable and uncontrolled. In fact, naturally occurring changes in light among different images along the day are actually desired and exploited, producing an enhanced multi-layer dynamic texture that is not limited to a frozen RGB colour map. These layers contain valuable complementary information about the depth of the geometry, surface normal fine details and other illuminationdependent parameters, such as direct and indirect light and projected self-shadows, allowing an enhanced and re-illuminable ortoimage representation.
Highlights
1.1 State of the art Nowadays the use of diverse software tools for photogrammetric and image-based dense 3D reconstruction is widely generalized in cultural heritage digitization
One obvious limitation of these methods resides in the fact that even when the objects are accurately photo-textured, and regardless of the method used to map the colours, the reproduced surface texture of the orthoimage will be a static snapshot frozen onto the surface of the object, resembling only the existing conditions at the moment of the acquisition
We focused in developing methods able to simultaneously determine the three-dimensional shape of the object and to map the surface appearance and environment illumination simultaneously as a lightmap, determined indirectly, instead of a set of well known point sources
Summary
1.1 State of the art Nowadays the use of diverse software tools for photogrammetric and image-based dense 3D reconstruction is widely generalized in cultural heritage digitization. To acquire a non-homogeneous texture mapping of the surface properties, most of the approaches proposed so far require active and variable illumination set-ups, such as domes (Klein and Schwartz, 2010), (Schwartz and Klein, 2012) or goniometer style arms (Haindl and Filip, 2013) and/or rotating tables These typically require a very large amount of photographs, taken from different known camera positions and commuting multiple point light sources. We focused in developing methods able to simultaneously determine the three-dimensional shape of the object and to map the surface appearance and environment illumination simultaneously as a lightmap, determined indirectly, instead of a set of well known point sources This would allow to work with hand-held digital photographs taken under variable but flexible illumination (including natural light) and would define an approach to appearance capture as practical and flexible as standard MVS, which can be used successfully in a variety of situations and environments, very for architectural and outdoor objects
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
