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• Imaging spectroscopy discloses the secrets of Picasso's painting "La Copa Blava". • Reflectance hyperspectral imaging enabled visualisation of earlier versions of the painting. • New-insights on the Picasso Blue period are gained with imaging spectroscopy. • Reflectance hyperspectral imaging has a potential for museums educational tasks. Reflectance hyperspectral imaging (HSI) in the Visible and Near-IR (VNIR) to the Short Wave IR (SWIR) ranges is acknowledged as one of the most effective techniques for non-invasive examination of paintings. Recently, in some important museums worldwide a new trend has emerged towards a more systematic use of reflectance HSI, which is applied as advanced imaging technique to attain at once analysis and documentation of the painted surfaces and inner layers. As an example of this trend, in the framework of the interdisciplinary program "Picasso: Blue Project" recently carried out at the Museu Picasso in Barcelona, a selection of paintings of the Blue Period (1901–1904) collection were revisited through the eye of cutting-edge analytical techniques, including reflectance HSI. The present paper focuses on the painting "The Blue Glass" (La Copa Blava, 1903), which was examined by using a high-performance reflectance HSI instrumentation. Under its visible surface, this iconic oil on canvas featured a stratification of different compositions that perfectly witnessed the Picasso's creative process. The HSI data enabled an unprecedented visualisation of the artistic metamorphosis of this painting. The well-known Picasso's creative practice of repainting on his own canvas was brought to the light by means of HSI images, which offered unique materials for visualising the hidden layers of the painting, by disclosing subsequent and unknown earlier versions and the artistic evolution of the painting. The outcomes of the project were disseminated in an exhibition, that addressed the ambitious objective of sharing with the wide public scholarly advanced knowledge hitherto gained on the Picasso Blue Period. Within this context, reflectance HSI proved to be exceptionally effective, not only for addressing analytical tasks, but also for educational purposes. [ABSTRACT FROM AUTHOR]

This work explores the potential of a compact hyperspectral camera, Specim IQ, for the remote colorimetric study of polychrome surfaces in controlled environments. These measurements are generally made with dedicated instruments, such as colorimeters or spectrophotometers, which require contact with the surface and coverage areas of the order of 10s of mm2. These two characteristics, contact and a very small analysis area, can severely limit the study of polychrome surfaces, since the measured areas are not necessarily representative of the entire surface. In addition, it is not always possible to touch the objects being analyzed. A possible alternative is the use of compact hyperspectral cameras, such as Specim IQ, for the in situ study of the spectral and colorimetric characteristics of these surfaces. To better address this research, which is still in the preliminary phase, a 2 × 45°/0° geometry measuringement was used. The illumination of the image plane at 45° with respect to the camera made it possible to eliminate the components reflected specularly on the camera lens. With this shooting geometry, Labsphere Color and Gray Reflectance Standards (eight color and four gray standards) were analyzed and placed on seven different color backgrounds. With the spectral data acquired, it was possible to calculate the color of the targets and display the colorimetric values by means of three commonly used image processing software packages. In this way, it was possible to define for this hyperspectral camera a measurement‐data processing procedure applicable to measurements in the laboratory aimed at studying the color of polychrome surfaces. [ABSTRACT FROM AUTHOR]

• Remote-sensing Hyperspectral Imaging (HSI) is applied in archaeological contexts. • A readapted avionic instrument was used for HSI in-field campaigns in Pompeii. • Mural paintings were non-invasively investigated with pigments identification. • A method for semi-quantitative mapping of gypsum on wall paintings was developed. • HSI technique proved to be usable to retrieve faded characters in mural inscriptions. Hyper-Spectral Imaging (HSI) is nowadays a well-established technology in the field of Cultural Heritage (CH), being acknowledged as a highly effective tool for accomplishing both non-invasive diagnostics and documentation of different typologies of polychrome artworks. Until recently, in CH field HSI technique has been mainly applied for investigating polychrome surfaces of small or medium size objects in museum collections, such as easel paintings, illuminated manuscripts or paper based artifacts. Conversely, the outdoor applications of HSI on large mural surfaces, wall paintings, frescoes and archeological assets are still mostly unexplored. This is due to the fact that the HSI systems designed for CH applications usually work at short-distance from the targets and can cover only limited size surfaces. To overcome this limitation, and to extend the applications of HSI to investigating mural paintings in external contexts, cloisters, ceilings, or assets in archaeological sites, a remote-sensing approach, based on the use of readapted avionic sensors, has been considered and tested in-field. This work illustrates the results of the measurements campaigns carried out in the archaeological site of Pompeii (Italy) by means of remote-sensing HSI technology. To this purpose, the high-performance prototype SIMGA, an avionic hyperspectral imager developed by Leonardo Company for earth-surface observations, was employed for the first time in an archeological context, within the framework of the wider project "Great Pompeii Project". HSI measurements were performed on different types of wall surfaces, including mural paintings and mural inscriptions. On the wall paintings, the acquired HSI data proved to be effectively usable for identification of most of pictorial materials and for mapping their distributions. The presence of gypsum as marker of degradation phenomena could be detected and mapped. On mural inscriptions, the HSI data could be suitably processed to enhance some vanishing traits, hardly perceivable by visual inspection. The proposed approach provided evidence that HSI is a promising tool to retrieve some faded parts of partially lost texts of mural inscriptions in archeological contexts. [ABSTRACT FROM AUTHOR]

RGB digital cameras (RGB) compress the spectral information into a trichromatic system capable of approximately representing the actual colors of objects. Although RGB digital cameras follow the same compression philosophy as the human eye (OBS), the spectral sensitivity is different. To what extent they provide the same chromatic experiences is still an open question, especially with complex images. We addressed this question by comparing the actual colors derived from spectral imaging with those obtained with RGB cameras. The data from hyperspectral imaging of 50 natural scenes and 89 paintings was used to estimate the chromatic differences between OBS and RGB. The corresponding color errors were estimated and analyzed in the color spaces CIELAB (using the color difference formulas ΔE*ab and CIEDE2000), Jzazbz, and iCAM06. In CIELAB the most frequent error (using ΔE*ab) found was 5 for both paintings and natural scenes, a similarity that held for the other spaces tested. In addition, the distribution of errors across the color space shows that the errors are small in the achromatic region and increase with saturation. Overall, the results indicate that the chromatic errors estimated are close to the acceptance error and therefore RGB digital cameras are able to produce quite realistic colors of complex scenarios. [ABSTRACT FROM AUTHOR]