Advanced Imaging Techniques
- Page under construction: current content is likely to focus on techniques of use for the scanning of inscribed surfaces
- Please add information, links to discussions of further information, or headings you would like to see populated
3D Surface Scanning
3D laser scanning can be achieved via a variety of techniques:
- Laser triangulation (a known laser pattern from a known position relative to a sensor is beamed onto a surface and the resulting distortion is triangulated to calculate depth)
- Time-of-flight (a laser is pulsed and the time it takes to return is used to calculate depth)
(See also DC 2008 Paper by Ryan Baumann.)
Photogrammetry encompasses a number of different techniques which reconstruct 3D information from 2D photographs.
- See: http://en.wikipedia.org/wiki/Photogrammetry
- See also SunoikisisDC photogrammetry training:
- March 2016: 3D imaging, scanning and printing
- November 2017: 3D scanning and imagng
- October 2018: 3D imaging and printing
- October 2019: 3D imaging and photogrammetry
- Jan 2021: 3D imaging and photogrammetry
- Mar 2021:Publishing 3D models and intellectual property
- July 2021: Beyond Classics: The Book of the Dead in 3D
3D Volumetric Scanning
CT scanning involves computing a 3D model from a number of X-ray projections taken around an object. Due to the nature of this technique, contrasts in a typical CT scan will correspond to contrasts in the material's X-ray absorption properties. See: http://en.wikipedia.org/wiki/Computed_tomography
MRI relies on the principal of introducing and imaging magnetic spin of specific isotopes, particularly Hydrogen. Due to the properties of MRI, this is typically most suitable for liquids ("solution-state") and MRI of solid materials is relatively difficult (though higher fields and short T2 times, as well as developing techniques such as MAFS/MARF may enable non-destructive MRI of solid materials). As a result, it is highly suitable to certain applications (i.e. medical imaging, due to the prevalence of water in the human body) but its application to imaging of archaeological artifacts is sparse. A non-metallic object could in theory be imaged with MRI by immersing it in water before imaging to obtain a negative image of water permeation, but this is unlikely to be suitable for cultural artifacts.
Optical Coherence Tomography
Advanced 2D Imaging
Polynomial Texture Mapping
Polynomial Texture Mapping (PTM) or Reflectance Transformation Imaging (RTI) involves taking multiple images of an object under different lighting conditions, e.g. multiple raking light positions. These are then combined and stored in a single image such that the light can be manipulated while viewing, or processing can be applied to bring out details. Its combination of low cost, high resolution, ease of use, high portability, and ability to capture fine incisions in surfaces has led to it being used for imaging a number of cultural heritage artifacts, including the Antikythera Mechanism. See: http://en.wikipedia.org/wiki/Polynomial_texture_mapping
See this post to the RTI_Help mailing list for an explanation of the history of the terms "PTM" and "RTI".
Multispectral/hyperspectral imaging involves capturing a material's spectral reflectance across a wider/finer range of the electromagnetic spectrum than a typical RGB image. This information can be used to more accurately reproduce color (avoiding metameric failures), distinguish between or classify inks, or be fed to image processing algorithms for visualization. See: http://en.wikipedia.org/wiki/Multispectral_image
X-ray fluorescence (XRF) is a spectroscopy technique wherein an object is exposed to high-energy X-rays and imaged for characteristic fluorescence of specific elements.
Researchers at Cornell have used XRF to reveal trace elements left in incised text by painting, environmental exposure, or chisel work:
- "Scientists and humanists join forces to use X-ray technology to shed new light on ancient stone inscriptions", Cornell Chronicle
- J. Powers, N. Dimitrova, R. Huang, D.-M. Smilgies, D. H. Bilderback, K. Clinton and R. E. Thorne: "X-ray fluorescence recovers writing from ancient inscriptions", Zeitschrift für Papyrologie und Epigraphik (Bonn, Germany) 152, 221-227 (2005).
- J. Powers, N. Dimitrova, R. Huang, D.-M. Smilgies, D. H. Bilderback, K. Clinton and R. E. Thorne: "Recovering Ancient Inscriptions by X-ray Fluorescence", Research Highlight, CHESS News Magazine 2005, p. 60-63.
- J. Powers, et al.: "X-ray fluorescence imaging analysis of inscription provenance", Journal of Archaeological Science, Vol. 36, Issue 2, 343-350 (2009).