AIC's 46th Annual Meeting

Multispectral imaging has become a critical analytical tool in the examination and documentation of cultural heritage. But despite the popularity of this technique there are numerous impediments to standardization and repeatability. Within a single institution, the Metropolitan Museum of Art, we found that approaches to capture, processing, archiving methods and even terminology varied significantly between the various conservation labs. This talk will introduce the ways in which the Met has begun to address these issues, and will focus specifically on our efforts to standardize a reliably repeatable in-house image capture workflow that can be adopted both internally, and across institutions. Our work is indebted to the CHARISMA project (Cultural Heritage Advanced Research Infrastructures: Synergy for a Multidisciplinary Approach to Conservation/Restoration) spearheaded by the British Museum. CHARISMA made great strides in presenting a capture methodology and an open source solution for standardization of post processing; however, our efforts at unifying our results through CHARISMA met with limited success. Rather than relying on post-processing to standardize results, our methodology uses scene referred capture, which uses targets to correct for color, tone, and white balance during the capture process to achieve a successful image regardless of the camera, lens, and light source used for capture. We started by creating a protocol to capture visible light images, the backbone of which leverages the new ISO19264 artwork reproduction standards. Images are captured using an X-rite Color Checker Digital SG Card and a Munsell Linear Grayscale, and we chose to use Adobe Lightroom to evaluate captured images, as it is one of the few applications that gives a read-out for L* values. Through the evaluation of the targets, we are able to obtain a color profile that falls within the acceptable range of color fluctuation as defined by ISO and tone curve for any camera and lighting set-up that can be applied to all subsequent images. The same color profile and tone curve obtained through this process can then be applied to the multispectral imaging suite, including Ultraviolet-induced Visible Luminescence imaging, Visible-induced Infrared Luminescence imaging, Ultraviolet-reflected imaging and Infrared-reflected imaging. Through using this workflow, we have found that one is able to achieve repeatable, high quality images and produce similar results across multiples set ups. This paper will share the step-by-step details of this workflow and case studies for which this workflow has been applied in Objects Conservation, Paper Conservation and other labs at the Met. Additionally, ongoing research on light sources and other aspects of multispectral imaging practice will be presented.