High-Accuracy Digital Imaging of Cultural Heritage without Visual Editing

Abstract

At Rochester Institute of Technology, a research program is near completion aimed at benchmarking the quality of direct digital imaging of cultural heritage in American museums, libraries, and similar institutions. The current practice at nearly all institutions surveyed includes visual editing. Digital masters incorporate camera spatial processing, ICC-type color management including encoding in a large-gamut RGB space, and global and local visual editing. Also at RIT, a research program is underway aimed at developing a high-quality digital camera that incorporates spectral imaging. The hypothesis is that when using the new camera system, visual editing is unnecessary, greatly improving workflow efficiency and color accuracy. An experiment was performed to test this hypothesis. The experiment included spectral-based imaging of both color targets and small paintings and rendering the spectral images for a colorimetrically-characterized computer-controlled LCD display. The targets and paintings were viewed adjacent to the display in a laboratory lit by ceiling-mounted daylight-balanced fluorescent lights. A variety of quantitative comparisons were performed including: reflectance spectrophotometry vs. insitu spectroradiometry, reflectance spectrophotometry vs. spectral-based imaging, forward and inverse model accuracy of the LCD colorimetric characterization, and in-situ spectroradiometric comparison of targets and paintings compared with their LCD renderings. Using the GretagMacbeth Color-Checker as an independent verification target, average color differences varied between 1.0 and 2.9 ΔE00. For two paintings, the average accuracy was 4.2 and 5.1ΔE00. This level of accuracy exceeded that achieved by museums and libraries, even following global and local image editing, confirming our hypothesis that it is possible to create a digital archive of cultural heritage without the need for visual editing.