敦煌壁画绘画材料多光谱图像标准数据库的建立和应用

摘要

Multispectral imaging techniques are based on the facts that each substance has a characteristic ab-sorbance and reflectance spectrum.Besides,it takes into consideration the fact that the corresponding color bi-ases in different monochromatic spectral ranges may be enhanced by converting the monochromatic greyscale image into a false-color image.Thus,multispectral imaging may be applied to the investigation of painting ma-terials.It is,however,necessary to first establish a multispectral image database for archeological painting materials.Such a database would enable multispectral imaging to be used to conduct preliminary surveys on undecipherable sections of murals,pigments of similar hue,and organic materials that cannot be observed un-der visible light.The preliminary survey results may then be used as a basis for more detailed studies conduc-ted using high-precision instruments.In this study,a standard pigment color chart was created using the 29 painting materials that are known to have been used in the Dunhuang murals.Reflectance and fluorescence im-aging of the pigments was performed in various spectral ranges between 250 and 1300 nm,using a standard-ized multispectral imaging procedure under optimized multispectral imaging conditions.The resulting data were then post-processed and combined with infrared (IR)and ultraviolet (UV)reflectance false-color images for use in the preliminary construction of a standard multispectral image database for the painting materials used in the Dunhuang murals.Multispectral imaging was then performed on actual murals to simultaneously collect visible,IR,and UV reflectance false-color images that were then compared with the standard image database. The multispectral imaging results were analyzed via comparisons with data obtained using portable microscopy, portable x-ray fluorescence spectrometry,and near-infrared spectroscopy.The results show that the establish-ment of a standard multispectral image database for mural painting materials can be applied as a new nonde-structive analytical method.This method can be used in the preliminary verification of painting materials used in the Dunhuang murals,to identify the properties of the painting materials,and to obtain information such as pigment distributions.The establishment of this database will also increase the reliability and effectiveness of preliminary studies on the type and scope of commonly observed painting materials.Thus,it is expected to be useful in pigment studies.%多光谱摄影图像调查技术,基于不同物质对不同光谱吸收与反射的差异及不同波段单色光谱有相应的灰度偏向,以单色光谱灰度图像经伪彩色强化,可作为一种绘画材料普查方法.这种方法的应用首先需要建立相关遗址绘画材料多光谱图像标准,以此为基础才可以通过多光谱伪彩色等图像对壁画中漫漶壁画、相近色相颜料及无法观察的有机材料做前期普查,为后期高精度仪器的进一步调查提供参考.采用已知敦煌壁画中常用29种绘画材料制作标准颜料色板,通过规范多光谱拍摄程序和优化多光谱拍摄条件,在250~1300 nm之间获取各种颜料在不同光谱区域的反射及荧光图像,再经过后期科学的图像校正及红外、紫外反射伪彩色图像合成,初步建立敦煌壁画颜料多光谱图像标准数据库.对真实壁画进行多光谱拍摄,将获取的可见反射、红外反射伪彩色和紫外反射伪彩色图像与标准数据库图像进行交叉对比,并采用便携式显微镜、便携式X荧光、近红外光谱等分析技术验证所获取的多光谱分析结果,表明壁画颜料多光谱图像标准数据库的建立,作为一种新型无损检测辅助方法,可通过多光谱图像对敦煌壁画颜料前期鉴别、推断绘画材料属性以及获取颜料分布状况等信息.绘画材料光谱图像数据库的建立可提高常见绘画材料类别及范围的前期调查效率和可靠性,是一种有效的颜料面集调查辅助方法.