Abstract

"Wouldn't it be better if 99% of institutions were working toward 99% accuracy, rather than 1% of institutions working toward 100% accuracy?" — John Barrett (Senior Photographer, Bodleian Libraries) during the AHFAP panel discussion "The Practical Implementation of Imaging Standards" in February 2022. In an increasingly virtual world, cultural heritage collections are more frequently experienced on a screen than in person. For especially precious or ephemeral works, reproductions may serve as the primary means of interacting with them. Often, series of works or related pieces are held in different collections, and it may be logistically complicated to exhibit them together physically. Additionally, many artists' materials have finite lifetimes. Imaging an object provides a snapshot of a material's appearance at a specific moment in time, serving as conservation documentation and/or a means to simulate what it may have looked like in the past, and what it may look like as physical changes continue in the future. In all of these situations, it is critical to capture, document, and share an object's true appearance. Fundamentally, this begins with the accurate capture of color. Color is central to the character and physical essence of a work of art, and shapes the viewer's experience and understanding. Yet, studio reproductions often fall short of accurately representing the color of the real object. Carefully controlled conventional color imaging goes a ways toward faithful color rendering, but spectral imaging has emerged as a more reliable and increasingly attractive means of accurate color capture. In the context of cultural heritage imaging, spectral imaging was once strictly a scientific laboratory analysis, but the opportunity to implement this technique within routine studio photography workflows has emerged as it has matured. This dissertation shares the spirit expressed in the quote above, exploring the sentiment that access to excellence should be universal, through the lens of practical spectral imaging techniques and technologies. The research described within lays out the groundwork for a low-cost, low-complexity approach to spectral imaging focused on highly accurate color reproduction. An efficient, studio-friendly capture technique called "two-light imaging" is demonstrated using a commercially available, professional level camera and tunable, multichannel LED lights. Proof-of-concept experiments in which the color accuracy of two-light imaging was compared with conventional color imaging and the earlier, filter-based spectral capture method of "dual-RGB imaging" were conducted first, to emphasize benefits of spectral imaging over conventional color imaging, and to illustrate trade-offs between LED- and filter-based spectral band selection methods. The effect of camera choice, lens choice, and IR modification on color accuracy were then simulated using the camera sensitivity measurements of several dozen prosumer cameras to explore the robustness of two-light imaging to generalization across common cameras. Next, a user-friendly software application called Beyond RGB was developed to facilitate the colorimetric calibration process for two-light image sets. Finally, two-light imaging was presented at several institutions, where the goals of the project were discussed and the capture and processing strategies were demonstrated in effort to share spectral imaging at a more accessible level. This work was carried out specifically to promote the adoption of spectral imaging at smaller institutions where scientific imaging has previously been out of reach. Improved access to and support for advanced imaging empowers a larger group of cultural heritage imaging professionals, and ultimately enhances stewardship of our heritage collections.

Library of Congress Subject Headings

Spectral imaging; Cultural property--Imaging; LED lighting

Publication Date

2-2023

Document Type

Dissertation

Student Type

Graduate

Degree Name

Color Science (Ph.D.)

Advisor

Susan P. Farnand

Advisor/Committee Member

Joseph P. Hornak

Advisor/Committee Member

Mark D. Fairchild

Campus

RIT – Main Campus

Plan Codes

CLRS-PHD

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