Hyperspectral Pigment Analysis of Cultural Heritage Artifacts Using the Opaque Form of Kubelka-Munk Theory

TL;DR

This study applies the single-constant Kubelka-Munk theory to hyperspectral data of a 17th-century Chinese map, aiming to classify and analyze pigment distribution in cultural heritage artifacts using spectral imagery.

Contribution

It demonstrates the utility of analyzing hyperspectral data in the K/S space for pigment classification, offering an alternative to traditional reflectance domain methods in cultural heritage analysis.

Findings

Successful classification of green pigments in the map

Identification of spatial patterns in pigment distribution

Assessment of the K/S space approach's effectiveness

Abstract

Kubelka-Munk (K-M) theory has been successfully used to estimate pigment concentrations in the pigment mixtures of modern paintings in spectral imagery. In this study the single-constant K-M theory has been utilized for the classification of green pigments in the Selden Map of China, a navigational map of the South China Sea likely created in the early seventeenth century. Hyperspectral data of the map was collected at the Bodleian Library, University of Oxford, and can be used to estimate the pigment diversity, and spatial distribution, within the map. This work seeks to assess the utility of analyzing the data in the K/S space from Kubelka-Munk theory, as opposed to the traditional reflectance domain. We estimate the dimensionality of the data and extract endmembers in the reflectance domain. Then we perform linear unmixing to estimate abundances in the K/S space, and following Bai, et al. (2017), we perform a classification in the abundance space. Finally, due to the lack of ground truth labels, the classification accuracy was estimated by computing the mean spectrum of each class as the representative signature of that class, and calculating the root mean squared error with all the pixels in that class to create a spatial representation of the error. This highlights both the magnitude of, and any spatial pattern in, the errors, indicating if a particular pigment is not well modeled in this approach.