Integrating Spectral and 3D Imaging for Monitoring Heritage Objects E. Keats Webb

Conservation Documentation

Scientific Imaging

CollectionsPhotography

Measurement and Material Identification

Exhibition and Catalogue

Record Condition, Inform Care, and Increase Understanding

Smithsonian National Museum of the American Indian Inka Qero (NMAI 16/3605)

Museum Imaging

UV-Induced Visible Luminescence Visible Reflected IR

Smithsonian American Art MuseumUntitled (SAAM 1986.65.339)

Spectral and 3D Imaging

Accessible Devices and Workflows

Smithsonian American Art MuseumUntitled (SAAM 1986.65.339)

Visible

Reflected IR

Smithsonian American Art MuseumUntitled (SAAM 1986.65.339)

Camera Modification• Single wavelength conversion • Full spectrum conversion • Monochrome conversion

Dust reduction filter

Sensor

IR blocking filter

Microlens

Blue color filter

Photodiode and Silicon Substrate

Modified Consumer Digital Camera

Camera Characterization

7

Spectral Response • Spectral response showed

higher sensitivity in the shorter wavelengths

2D Image Quality • RAW processing workflow that accounts for the camera modification

• Residual pixel-level pattern

• Increased noise

• Increased effective resolution but risk of aliasing

Wavelength selection Object materials

& Optical Properties

Camera Sensitivity

Filter Transmission

Illumination Output (SPD)

Depth of Field and Sharpness Depth of field is not well defined for 3D reconstruction

f/5.6 f/11 f/32

Work to Quantify Effective Depth of Field • Linking 2D image quality assessment to 3D reconstruction

• Permissible blur:

• FADGI star rating requires smaller value

• 3D reconstruction tolerates larger value

• Test object is not representative of heritage objects

Summary

Wavelength selection with the modified camera• Increase local contrast to improve 3D reconstruction

Understanding depth of field for 3D reconstruction • Increase sharpness to improve 3D reconstruction

Camera Characterization

Linking 2D image quality to 3D reconstruction

Acknowledgements Museum Conservation Institute

Robert Koestler, DirectorPaula DePriest, Deputy Director

Smithsonian American Art MuseumAmber Kerr, Chief of ConservationHelen Ingalls, Retired Objects ConservatorAriel O’Connor, Objects Conservator

University of Brighton Roger Evans, Reader

University College LondonStuart Robson, Professor of Photogrammetry and

Laser Scanning Lindsay MacDonald, Honorary ProfessorDanny Garside, PhD StudentBen Sargeant, PhD Student

Analytik LtdIan Laidlaw, Managing Director & Founder