Type: (Multi/Hyper Spectral) Imaging
Overview
Hyperspectral imaging is a chemical imaging technique based on reflectance spectroscopy (the light reflected by materials). This device makes the collection of reflectance spectra in each point of the field of view for the Near Infrared range (it is complementary to another device for the visible range). The hyperspectral image cube obtained can be considered both as a stack of wavelength-resolved images and as a series of spectra.
The near infrared spectra consist of vibrational overtones and combination absorption features where spectral signatures can allow to identify and map different materials.
This technique is well adapted to characterize organic compounds (binding media, plastic materials…) and some minerals.
Hyperspectral Imaging provides spatially resolved information on the nature of chemical species that can be interesting to locate damages (moisture, chemical transformations…), restorations, pentimenti or underdrawings on/in an artwork.
Hyperspectral imaging is well adapted for flat or slightly embossed artworks (manuscript, drawing, paintings,…)
Near Infrared hyperspectral imaging is a non-invasive, in situ technique that allows to collect data cube in few minutes without any preparation of the artwork.
Technical details
The system consists of an ImSpector N25E imaging spectrograph (Specimcorp, Finland) and a cooled, temperature stabilized MCT detector (9.6 mm detector having 320 (spatial) x 256 (spectral) pixels).The camera operates from 970 to 2500 nm with a spectral resolution of 10 nm. It works as a line scan camera providing full, contiguous spectral data for each pixel.
The cooling system (dual Peltier solution, forced convection coolers) is designed to minimize dark current and ensure high stability in the detector operations in a wide ambient temperature range.
Two objective lenses are available:
- A telecentric lens with a focal length of 15 mm (corresponding to a minimal field of view of 20 cm and a maximal resolution of 600 µm)
- A macroscopic lens with a 1:1 magnification (corresponding to a field of view of 9.6 mm and a spatial resolution of 30 µm)
The camera is moving along a motorized bar of around 1.6 m, resting on a portal frame structure. The height of the structure is around 2 m. The artwork is illuminated with 6 halogen lamps (three on each side) placed at 45 degrees from the vertical. The current structure is designed to scan artefact laid flat on a tablebut the configuration can possibly be changedto scan artefact in a vertical position.
Further readings
- Dooley, K.A., Lomax, S.,Zeibel, J.G., Miliani, C., Ricciardi, P., Hoenigswald, A., Loew, M., Delaney, J.K.,”Mapping of egg yolk and animal skin glue paint binders in Early Renaissance paintings using near infrared reflectance imaging spectroscopy”, Analyst, 138, 4838-4848, 2013.Ricciardi, P.,
- Delaney, J.K., Facini, M., Zeibel, J.G., Picollo, M.,Lomax, S., Loew, M.,”NearInfraredReflectance Imaging Spectroscopy to MapPaint Binders In Situ on IlluminatedManuscripts”,AngewandteChemie International Edition 51, 5607-5610,2012.
- Cséfalvayová, L., Strlič, M., Karjalainen H., “Quantitative NIR Chemical Imaging in Heritage Science”, Analytical Chemistry 83, 5101-5106, 2011.
- Delaney, J.K., Zeibel, J.G., Thoury, M., Littleton, R., Palmer, M.,Morales, K.M., René de la Rie, E., Hoenigswald, A.,”Visible and infrared imaging spectroscopy of Picasso’s Harlequin musician: mapping and identification of artist materials in situ”, Applied Spectroscopy 64, 584-94, 2010.
- Baissa, R.,Labbassi, K., Launeau, P., Gaudin, A., Ouajhain, B.,”UsingHySpex SWIR-320m hyperspectral data for the identification and mapping of minerals in hand specimens of carbonate rocks from the Ankloute Formation (Agadir Basin, Western Morocco)”, Journal of African Earth Sciences 61, 1-9, 2011.
Providers
MOLAB France: CNRS