IRIS: a novel spectral imaging system for the analysis of cultural heritage objects

Abstract

A new portable spectral imaging system is herein presented capable of acquiring images of high resolution (2MPixels) ranging from 380 nm up to 950 nm. The system consists of a digital color CCD camera, 15 interference filters covering all the sensitivity range of the detector and a robust filter changing system. The acquisition software has been developed in "LabView" programming language allowing easy handling and modification by end-users. The system has been tested and evaluated on a series of objects of Cultural Heritage (CH) value including paintings, encrusted stonework, ceramics etc. This paper aims to present the system, as well as, its application and advantages in the analysis of artworks with emphasis on the detailed compositional and structural information of layered surfaces based on reflection & fluorescence spectroscopy. Specific examples will be presented and discussed on the basis of system improvements. INTRODUCTIONSpectral imaging is a well-known methodology for the analysis of paintings with high spatial resolution [1]. Through the years a number of systems have been developed to fully exploit the advantages offered by this technique in mapping the compositional and stratigraphic information of the analysed surfaces [2]. The design of these instruments is based on two different principles of operation. In the first one the white light reflected by the object is analyzed by imaging monochromators resulting into images of high spatial but limited spectral information [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Their advantages is that they can be operated under any lighting conditions and thus allow for field measurements. The second one is based on the illumination of the object by monochromatic light providing high spatial as also spectral information [18,19]. Its main disadvantages are the limited scanning speed, as well as, the restriction for limited environmental lighting upon operation. In-house or laboratory measurements can be performed with both techniques, since the environmental light conditions are easily controlled. On the contrary field measurements using ambient day light promote imaging monochromators as the only choice. Analytical problems requiring the application of both techniques simultaneously do exist and are based on the fluorescence spectral imaging [20][21][22]. In this case, researchers need to control the illumination wavelength for excitation as also to record the full fluorescence spectrum with high spatial resolution. In this work we are presenting an imaging monochromator, with emphasis on portability and robust structure to enable reliable field measurements, which also allows for high spatial and spectral resolution. The system IRIS [23] incorporates a high resolution CCD sensor (2 MPixels) along with a spectral resolution of 15 band-pass filters, ranging from UV (380 nm) up to NIR (950 nm). The system is mobile, very robust, sensitive and easy to be controlled by the end-users. The operating software is tailor made and has been developed in LabView ...

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