Colour & Space in Cultural Heritage (COSCH): a training school on hyperspectral imaging
By E. Keats Webb
In December 2014, the COST (European Cooperation in Science & Technology) Action: Colour & Space in Cultural Heritage (COSCH) brought together professionals from throughout Europe for a Training School on hyperspectral imaging of 2D polychrome surfaces. The training school took place at the Institute of Applied Physics a part of the Italian National Research Council (IFAC-CNR) outside of Florence, Italy.
Hyperspectral imaging is the collection of images at many different wavelengths over a larger spatial area with bandwidths of a few nanometres or less (Ricciardi et al. 2013). This imaging results in image cubes that can produce reflectance spectra at each point allowing for non-destructive material identification. The training focused on the IFAC-CNR custom designed hyperspectral scanning system (Cucci et al. 2013). Due to the scanner’s highly specialized nature and long scanning time, hands-on training was not provided, so this training presented possibilities for the processing and visualisation of data.
Marcello Picollo and his team at IFAC-CNR, Andrea Casini, Costanza Cucci, and Lorenzo Stefani, hosted the workshop and provided presentations and three site visits. Lectures covered spectral imaging; artists’ materials and their VIS-NIR spectral features; hyperspectral imaging devices, data acquisition, and data processing; and hyperspectral data access, management, and visualisation. The site visits included a tour of the San Marco Museum by the museum’s director, observing a hyperspectral scanner at the Opificio delle Pietre Dure built by the National Institute of Optics (INO) of the CNR (Daffara et al. 2010), and viewing the IFAC-CNR scanner in the Restoration Labs at the Uffizi.
Conservators, curators, imaging specialists, and professionals outside of the heritage realm came together for the training school to learn more about the acquisition and processing of hyperspectral data from the custom-built IFAC-CNR scanner, which lead to discussions about the spectral imaging work being done throughout European institutions. The coffee breaks between lectures and the dinners following sessions provided fertile grounds for debating and discussing elaboration of spectral data, standardisation, device independence, and comparison of data. The multidisciplinary attendants provided a unique perspective on the range of challenges for spectral imaging in heritage science.
An underlying issue with spectral imaging within heritage science is the lack of standardisation of fundamental vocabulary including multiband, multispectral, and hyperspectral imaging. Building on the challenges of language and standard definitions, the range of equipment used for acquiring multispectral and hyperspectral image data presents challenges for the standardisation of the techniques and the comparison of data from different systems or different institutions. The inherent large file size of hyperspectral data presents issues with distribution, access, and storage. Hyperspectral data is used by a range of professionals for a variety of applications, and the lack of accessible software has led to self-built solutions targeted at specific data-acquisition or elaboration needs (Micheletti 2014).
COSCH Working Group 1 (WG1) focuses on spectral object documentation including the task of “Identification, characterization and testing of spectral imaging techniques in the visible and near IR”, which includes exploring the limits and advantages of different devices (COSCH). The WG1 research projects are working to address the issues and challenges of spectral imaging within heritage science. One of these projects includes a Round Robin Test (RRT) to assess the various hyperspectral imaging systems being used at heritage institutions. Four objects in addition to a white card are being analysed by at least sixteen institutions with various multi- and hyperspectral systems (Vitorino 2014). The RRT is a coordinated research effort to better understand the instrumentation, elements of data acquisition, and the effects of the instruments and methodology to the accuracy and reliability of the data. This will help with standardising methodologies and presenting best practices.
The Training School on hyperspectral imaging at IFAC-CNR provided a great opportunity to learn more about hyperspectral imaging within Europe, to meet a network of heritage professionals doing cultural heritage imaging, to connect with a research institute furthering the capabilities of spectral imaging for heritage science, and to learn about and become involved with the COST Action of Colour & Space in Cultural Heritage (COSCH).
COSCH—Colour & Space in Cultural Heritage, http://cosch.info
Cucci, C., et al. 2013. Extending Hyper-Spectral Imaging from VIS to NIR spectral regions: a novel scanner for the in-depth analysis of polychrome surfaces. In: Pezzati, L., Targowski, P. (eds.) Optics for Arts, Architecture, and Archaeology IV 8790 pp 879009-1-9. doi: 10.1117/12.2020286
Daffara, C, et al., 2010. Scanning Multispectral IR Reflectography SMIRR: An Advanced Tool for Art Diagnostics. Accounts of chemical research 43(6): pp847-856.
Micheletti, F. 2014. CRISTINA—Hyperspectral data access, management and visualization [training school presentation]. COSCH Training School: Hyperspectral Imaging Techniques Applied to the Investigation of 2D Polychrome Surfaces. 10-12 December 2014. Florence, Italy.
Ricciardi, P. et al. 2013. Use of Imaging Spectroscopy and in situ analytical methods for the characterization of the materials and techniques of 15th century illuminated manuscripts. Journal of the American Institute for Conservation 52(1): pp 13-29.
Vitorino, T., Analysis of the Round Robin Test data acquired at IFAC-CNR [STSM report online]. 2014. Colour & Space in Cultural Heritage (COSCH). Ref: COST-STSM-ECOST-STSM-TD1201-310814-048809. http://cosch.info/exchange-visits [Accessed 7 February 2015]