Guiding Principles of CHI Technologies

CHI logo  Worldwide expertise, collaboration
We collaborate with experts from around the globe in cultural conservation, computer imaging, museum and library sciences, natural sciences, and data archiving.

CHI logo  Compatibility, ease of adoption
Our imaging technologies are designed from the ground up to be compatible with current cultural heritage and natural history practices and digital-imaging skill sets.

CHI logo  Democratize technology
Our mission is to foster global dissemination and widespread adoption of robust digital documentary methods by reducing the barriers of cost and complexity.

CHI logo  Scientific reliability
To adopt the use of digital representations of physical objects, scholars must have confidence that the representations are reliable surrogates. Our tools provide the ability to track and reconfirm the quality and authenticity of the image data.

CHI logo  Long-term preservation
Perpetual digital conservation can ensure that digital representations of physical objects will be archived and available for future generations. CHI focuses on semantically-based knowledge management strategies and their use in simplifying methods of long-term preservation.

Testing for an RTI session at The Legion of Honor, San Francisco: Anthropoid Coffin, 4th century–3rd century BC, Egypt


Overview of CHI Technologies

Reflectance Transformation Imaging (RTI)  Photogrammetry  Digital Lab Notebook

Cultural Heritage Imaging (CHI) fosters the development and adoption of technologies for digital capture and documentation of the world’s cultural, scientific, and artistic treasures. We do this by collaborating with experts from around the world in cultural preservation, natural history collections, computer imaging science, museum/library science, and data archiving. The table on this page lists our core set of technologies and provides brief definitions of them. If you want more detailed information, including examples and documentation, follow the links below.

Computational Photography

  • A meta-term that applies generally to the set of digital photographic technologies we use at CHI
  • Based on the computational extraction of relevant information from a sequence of digital photographs
  • Extracted information is integrated into new digital representations to yield rich data not found in the original, individual photographs

image example: RTI

Reflectance Transformation Imaging (RTI)

  • A breakthrough class of imaging techniques used in cultural heritage and natural history documentation and preservation, enabling the study of the minute details of surfaces
  • Multiple photographs are taken of an object while light is projected from different angles
  • This lighting information is mathematically synthesized so that examiners can use a computer to analyze, “re-light,” and mathematically enhance the representation of the object’s surface
  • RTI tools provide flexible, cost-effective solutions for capturing shape and full-color digital imaging of cultural objects with extreme accuracy
  • Polynomial Texture Mapping (PTM) is a term referring to the first type of RTI imaging, invented by Tom Malzbender at HP Labs in 2001
photogrammetry sample


  • The practice of determining mathematical measurements and three-dimensional (3D) geometry data from two or more photographic images of the same subject
  • The human ability to see in three dimensions is based on the offset between the viewpoints of left and the right eyes
  • When photographs are taken from consecutive positions in an overlapping series, the resulting images mimic this perspective shift in viewpoint
  • These overlapping photographs can then be subjected to analysis using photogrammetric software
  • Resulting data integrates both optically corrected color imagery and 3D surface data that can be viewed, manipulated, and measured
  • Color information and 3D geometry is always perfectly aligned because the 3D geometry information is created from the color information in the overlapping photographs
digital lab notebook: example

Digital Lab Notebook, “born-archival”, and “empirical provenance”

  • “Digital lab notebook”: a CHI term that describes the digital process history record of the means and circumstances used to generate a digital representation (digital surrogate) of an empirically captured subject in the physical world
  • Once a digital surrogate and its associated digital lab notebook are archived, the information in the digital lab notebook aids current and future digital conservators in their preservation activities, enhancing the likelihood of the surrogate’s long-term preservation
  • The digital lab notebook also enables an archived digital surrogate’s qualitative evaluation of scientific reliability and suitability for reuse for novel purposes
  • “Born-archival”: a knowledge-management strategy guiding CHI’s next-generation software tools that “wraps” the digital surrogate, digital lab notebook, and original capture data into an easy-to-archive package containing the metadata necessary for the digital surrogate’s long-term management at significantly reduced preservation cost
  • “Empirical provenance”: a CHI term that distinguishes the process history metadata contained in the digital lab notebook from the provenance metadata, such as the material description and ownership history attributed to the digital surrogate’s empirically captured subject

Algorithmic pine cone rendering: courtesy of Szymon Rusinkiewicz, Princeton University.
Photogrammetry rock art image: courtesy of Tom Noble, US Bureau of Land Management.