Multispectral Imaging of Pigments with a digital camera and 12 interferential filters

Download are new paper “Multispectral Imaging of Pigments with a digital camera and 12 interferential filters“

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This paper illustrates the method that we’ll use for the “Multispectral Imaging for Art and Archaeology” crowdfunded project.

Abstract: This paper discusses a low-cost multispectral imaging system for the identification of pigments in artworks. It is composed of a full spectrum modified digital camera, a DSLR with the IR cut-off filter removed and sensitivity extended to about 360-1100 nm. A set of 12 interferential filters covering the range 400-805 nm completes the equipment. The system uses on-scene reflectance standards and the raw images are split in the 3 CFA (color filter array) components (RGB). An appropriate set of 12 RGB components was chosen to form the set of 12 spectral images to build up the reflectance imaging cube. This system was tested on a collection of 54 historical and modern pigments and their reflectance spectra were compared with a database of FORS spectra (360-1000 nm) of the reference pigments. The performance of this system was evaluated against a commercial spectral imaging system equipped with the same set of 12 filters, but mounting a conventional monochromatic high-sensitivity CCD. The performance of the digital camera system is comparable to that of the monochromatic CCD camera, but the latter provides more accurate spectra thanks to its higher linearity, especially at the edge of the spectrum and in the condition of low signal. The proposed system is of interest for the art conservation sector because of its low cost and because the same digital camera can be used for other technical photographic methods, reducing the weight and cost of the overall imaging equipment necessary. The proposed method implements a small number of filters and consequently it has limited analytical capacity. It must only be used for an initial mapping of the pigments and this preliminary identification must then be confirmed by elemental or vibrational spectroscopic methods.