untitled New Reflection Transformation Imaging Methods for Rock Art and Multiple-Viewpoint Display Mark Mudge Tom Malzbender * Carla Schroer Marlin Lum * Hewlett Packard Labs VAST/CIPA 2006, Nicosia Cyprus November 4, 2006 Topics • What is RTI? • How RTI works • Fundamental Understandings • Existing RTI Capture Systems • New Method, Highlight RTI • Multi-view RTI • Future Work Reflection Transformation Imaging (RTI) • Term coined by our coauthor Tom Malzbender and Dan Gelb of HP Labs, inventers of Polynomial Texture Mapping (PTMs) • Stores surface reflection information for each image pixel • 2D images with true 3D information • Information is image based, not requiring geometry in Cartesian space • No data loss from shadows and specular highlights • Mathematical explanation available at: hpl.hp.com/research/ptm RTI Basics • Fixed camera position • Multiple images illuminated from different known light positions • Images synthesized into a single RTI image • RTI captures “real world” reflectance characteristics of subject • Reflectance information generates perception of shape • Enhancement discloses additional information Ceramic Stamping Archaeologial Research Collection University of Southern California How RTIs work How RTIs work How RTIs work Fundamental Understandings • Digital technology for CH must be: – Adapted to the cultural heritage (CH) community – Adopted by the CH community – The result of early and on-going collaboration and evaluation with CH professionals – Freely available to the CH community Fundamental Understandings • Based on digital photography because those skills are already widespread • Compatible with existing skill sets and working cultures • Possible to automatically process the photos • No need for help from digital imaging experts during empirical data capture Fundamental Understandings • New Standards of Best Practice through: – New tools and methods – Worldwide communication – Pilot projects and demonstrations – Automatic “Empirical Provenance” Empirical Provenance • Access to process history and raw data • When included with digital representations of cultural heritage materials: – Permits the qualitative evaluation of digital information – Increases the acceptance of online information by scholars, educators, and the public – promotes collaborative, distributed scholarship •Now being mapped to the CIDOC/CRM Known Light Position RTI Capture Techniques HP’s RTI Capture Systems Photo: courtesy HP Labs Photo: courtesy HP Labs CHI’s Manual, Low Cost, Template System CHI’s Automatic RTI Capture Dome ISTI/CNR PISA Quality Assessment New Method: Highlight RTI No prior knowledge of light position needed Highlight RTI in the Field Rocha 2 da Ribeira de Piscos Parque Arqueologico Vale do Coa 5 June 2006 Highlight RTI in the Laboratory Instituto Portugues de Arqueologica Centro Nacional de Arte Rupestre 7 June 2006 Equipment Required • SLR digital camera • Light reducing neutral density filters • Tripods • Black ball on length and angle adjustable boom • Measuring tape • Retractable surveyors plumb-bob string (bob removed) • Light source – 1 to 1/32 power adjustable 320 watt second (minimum) flash - with battery pack and radio flash triggers *OR* – intensity adjustable continuous light - generator or indoors • Laptop Computer – remote camera control software – image viewing software (Photoshop, Irfanview, etc.) – black cloth Field Considerations • Ambient light – Use neutral density filters to block daylight • Light radius management – Illumination intensity central to accurate normal calculation – Low dynamic range in digital cameras – All the available histogram range used by incident light angle range Grazing Incident Angle ‘High Noon’ incident angle Estimating Lighting Direction From Highlight Location • V is the view vector pointing to the camera • N is the surface normal • L is the unknown, normalized light vector we solve for Prior use of spheres to collect lighting direction: Masseulus ‘02, Einarsson ‘04 Results: Goat Petroglyph 68cm by 46cm area Normal every 166 microns or 36 samples per sq. mm Results: Portable Rock Art ‘Portable Art’ - Magdalenian period (14,000 – 12,000 BP) Stone is 18 cm wide Normal captured every 65.7 microns or 231 per sq. mm Inset petroglyph is only 3.1cm in length Multi-View RTI • Multiple RTIs are captured from different viewpoints around the subject • These viewpoints are integrated in an interactive viewer • Image based 3D representation of objects from multiple viewing angles without 3D geometric models First Multi-view RTI: Collection Archéologie du Musée de l'Hospice du Grand St. Bernard Bronze Age Torque – 1600-2000 BCE Highlight RTI Future work • Automatically detect highlights on the ball • Make capture process more efficient • Explore stereo camera setup • Use 2 black spheres for precise light Positions • Explore non- photorealistic rendering Legend Rock, Wyoming Petroglyph Site August, 2006 Multi-View RTI Future Work: • Recent CHI funding from the U.S. Institute of Museum and Library Services (IMLS) National Leadership Grant will: – Create easy to use and cost effective Multi-View RTI capture techniques • Require only object placement and digital photography skill sets • Provide an automatic RTI processing pipeline • Compatible with existing professional cultures – Automatic generation of empirical provenance 3D Range Geometry Future work: • New research suggests possible automatic extraction of full 3D geometry from multi-view RTI image sequences • Geometry extraction enables: – Viewing from any direction – Measurement – Re-lighting from any direction or source – Reduction in the number of required RTI capture angles – Physical reconstruction, animation, and analysis of the subject Acknowledgements Thanks to: • Parque Arqueologico do Vale do Coa (PAVC) • Centro Nacional de Arte Rupestre (CNART) • Universidade do Minho • The Congregation of the Grand St. Bernard • Szymon Rusinkiewicz – Princeton • James Davis – UC Santa Cruz • U. S. Bureau of Land Management – Denver Technology Center, Archaeologist Mike Bies • CHI supporters and the CHI Board of Directors Contact mark@c-h-i.org carla@c-h-i.org www.c-h-i.org Copyright Cultural Heritage Imaging All Rights Reserved