Abstract
PRISMS (Portable Remote Imaging System for Multispectral Scanning) is designed for in situ, simultaneous high resolution spectral and 3D topographic imaging of wall paintings and other large surfaces. In particular, it can image at transverse resolutions of tens of microns remotely from distances of tens of metres, making high resolution imaging possible from a fixed position on the ground for areas at heights that is difficult to access. The spectral imaging system is fully automated giving 3D topographic mapping at millimetre accuracy as a by-product of the image focusing process. PRISMS is the first imaging device capable of both 3D mapping and spectral imaging simultaneously without additional distance measuring devices. Examples from applications of PRISMS to wall paintings at a UNESCO site in the Gobi desert are presented to demonstrate the potential of the instrument for large scale 3D spectral imaging, revealing faded writing and material identification.
Highlights
Spectral imaging was first developed for remote sensing and astronomy (Goetz et al, 1985)
If texture mapping is required at smaller spatial scales, individual images can be saved as the system is focusing which allows focus positions for sub-regions of each field of view (FOV) to be determined instead of the central region of interest (ROI)
In the case of the blue pigment, areas with a similar spectral shape at a more accessible height were examined with a portable Niton X-ray Fluorescence (XRF) spectrometer and found to contain copper which is consistent with the identification of azurite
Summary
Spectral imaging (i.e. multispectral and hyperspectral imaging) was first developed for remote sensing and astronomy (Goetz et al, 1985). A comparison between images in the visible spectral range with those in the near infrared can reveal past interventions and damages to the paintings, since conservators colour match the paint for retouching to the original without necessarily using the same paint material. Liang et al / ISPRS Journal of Photogrammetry and Remote Sensing 95 (2014) 13–22 a different position This is usually not a problem for very flat paintings such as easel paintings, but wall paintings by nature have significant 3D structure. We demonstrate a spectral imaging system that allows automatic, in situ, remote imaging (distances up to 35 m) of paintings at high resolution that gives spectral information per pixel of the paintings, and 3D position and distance measurements as a by-product.
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