PRISMS. Spectral imaging + 3D distance measurement = rich, useful datasets

When fresh scanning tools offer the ability to conduct ever-richer investigation of heritage material and provide documentation of an environment, it’s an exciting thing. According to an open-access paper published this month by Liaing et al in ISPRS vol. 95, that seems to be the case, with the team’s presentation of ‘PRISMS’ (Portable Remote Imaging System for Multispectral Scanning) which was designed “for portable, flexible and versatile remote imaging”. To quote what it is capable of:

“In this paper, 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 not only spectral information per pixel of the paintings, but also 3D position and distance measurements as a by-product.”

The specification of PRISMS is pretty impressive. The multispectral imaging can provide imagery at a resolution of 80 microns (0.08mm) from a distance of 10m, covering a range of 400-1700nm with a spectral resolution of 50nm. After calibration the 3D data capture achieved distance accuracy of ‘a few mm’, achieved at distances of 10m, though steadily worse at distances greater than that albeit with an indication of room for improvement with better calibration.

Sanskrit revealed in cave 465. Panel D shows 'difference image between 550 nm and 880 nm'.  Source:  Liaing et al (2014) http://www.sciencedirect.com/science/article/pii/S0924271614001336

Sanskrit revealed in cave 465. Panel D shows ‘difference image between 550 nm and 880 nm’.
Source: Liaing et al (2014)

The real-world applications have already been demonstrated: the paper shows that the tool revealed faded Sanskrit writing on the ceiling of China’s Mogao cave 465, otherwise not visible in solely colour and spectral imaging. In addition, it reveals invisible drawings and spectrally identifies pigments such as red ochre and azurite. 3D data capture and multispectral imaging have been possible separately by combining different tools previously, so the team’s development means a great deal for streamlining the investigation processes on-site and enabling easier, richer capture of heritage data.

Link to paper: http://www.sciencedirect.com/science/article/pii/S0924271614001336

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