Spectral reflectance estimation of ancient mexican codices, multispectral images approach

Abstract

Mexican codices are an ancient reading and writing system developed by the pre-Hispanic cultures of Mesoamerica. These pictorial documents are a cultural legacy, part of which dates from the 16$^{th}$ century. The collection known as ``Collection of Original Mexican Codices'' is one of the most important codices collection around the world and it is under the custody of the National Library of Anthropology and History~(BNAH, Biblioteca Nacional de Antropologia e Historia) in Mexico City. For preservation of the documents, the collection is kept under limited access and controlled illumination conditions, only tungsten lamps are allowed for illumination of codices and light intensity should no exceed 1000 Lux. In order to achieve accurate color reproduction of codices we have proposed to the BNAH a multispectral aproach. Our color reproduction method is based on the estimation of the spectral reflectance for every pixel in the image from a set of 16 bands multispectral images. Multispectral approach enables us to remove the original tungsten capture illumination and to carry out a color simulation under any arbitrary illumination, for instance CIE-D65, hence this approach enables us to reproduce the true colors of original codices. In this paper we present the results of several approaches for spectra estimation considering the illumination conditions established by the BNAH, and we show a color simulation of a codice replica under CIE-D65.