Non-Contact Color Analysis and Digital Archive Method for Blue-and-White Porcelain by Using Spectral Imaging Technology

Abstract

The unique colour representation of Oriental art work distinguishes itself from what has been seen in Western art work. Not only the traditional Oriental watercolour paintings but also the ancient Chinese porcelains show a great deal of interesting colours that have been archived by digital camera in digital archive practice. However, the majority of the current digital cameras operate with RGB filters, which record every pixel in a tri-chromatic manner. There are several limitations for such a tri-chromatic camera. One is that it describes the colour of the object only by three primary colours. Another is that the image captured is strongly influenced by the illumination at the scene, such that the archived image appears as it does specifically under that lighting condition, not as the original object itself. With such limitations, a problem called ‘metamerism’ may occur when an object is viewed under different illuminations. This creates a serious problem when colour is a critical factor in the digital archiving process. Spectral imaging technology is capable of capturing the colour in spectral form, and the spectral reflectance of each pixel is recorded accordingly. With consequent analysis and process, art works can be archived with high precision spectral data with the advantages of resolving the issue of metamerism and of reproducing the art work under any kind of illumination. Another advantage of spectral imaging technology is that it captures and analyzes the spectral data of an art work without any physical contact. In this study ancient Chinese blue-and-white porcelains collected by the Hwa-Kang Museum of the Chinese Culture University are digitised by spectral imaging technology. A custom-built spectral camera is used to capture the spectral image by using a new spectrograph device. Statistics analysis is used to extract the primary spectral reflectance from the captured spectral data. Comparisons can then be made to explore the differences among the colour primaries of the porcelains. This new spectral system and the colour analysis of blue-and-white porcelain as well as the resulting spectral characteristics of this porcelain can be a new benchmark for the museum community in digital archiving.