Advanced optical imaging methods for investigating manuscripts

This paper gives an overview of advanced optical imaging methods relevant to the study of manuscripts. While some of the methods covered are well established, others are very much in active development. ‘Optical’ in this context is loosely defined to cover the near ultraviolet, visible and the near infrared part of the electromagnetic spectrum. Optical imaging methods are in general non-destructive and can be applied in situ. They are non-invasive if care is taken to ensure a safe dosage of illumination during the imaging process. The examples given in this paper are biased towards work that the author has been involved in. This is by no means a comprehensive review. The aim of the paper is to illustrate how advanced optical imaging techniques can assist in the investigation of manuscripts

Multispectral acquisition of large-sized pictorial surfaces

Multispectral acquisition of artworks has recently received considerable attention in the image processing community. Quite understandably, so far this attention has mainly focused on paintings, given their predominant role in museum collections. It is worth pointing out that the instrumentation and procedures used for acquiring regular paintings are not suited for the multispectral acquisition of large-sized painted surfaces such as frescoed halls and great paintings. Given the relevance of such artifacts, and their widespread presence in churches or historical buildings due to their social function, the problem of finding suitable techniques for their acquisition is certainly worth addressing. This paper focuses on multispectral acquisition of large-sized pictorial surfaces, systematically addressing the practical issues related to the acquisition equipment and procedure. Given the crucial role played by the illumination in this application, special attention is given to this issue. The proposed approach is supported by experimental results

Colour-Difference Assessment for Driving Headlight Simulation

In high quality driving simulation applications, such as headlight simulation, colorimetric validity is essential. In virtual testing of headlight systems, it is important that the WYSIWYG (What You See Is What You Get) paradigm is respected for product quality headlight assessment. Indeed, if a slightly reddish orange colour is displayed instead of the typical orange of halogen lighting, the effect for driver comfort or traffic safety can be critical. The lighting specialist should accept a headlight which doesn't have the right colour. Previous studies have shown that there is a significant colour difference between virtual and real environments. Nevertheless, in virtual headlight testing the rendered colour fidelity has to fit industrial assessment. This study therefore deals with the colour-difference perceptibility that is the ability of an observer to detect a difference between two colours and, more precisely, on the acceptability of the perceived difference. We propose in this paper a psychophysical function for colour difference acceptability which fits well with the measured data. The colour acceptability function was implemented in a driving simulator for high validity headlight assessment. Driver acceptability experimentation was carried out using Renault's headlight driving simulation equipped with a fullcab and a 210° cylindrical display screen

Hyperspectral colour imaging and spectrophotometric instrumentation

The trichromatic nature of commercial photography is strictly connected with the nature of human colour vision, although the characteristics of usual colour imaging devices are quite different from the human visual system. The increase in the number of colour channels for spectral (either multispectral or hyperspectral) imaging is an active field of research with many potential applications in different fields. Each element of the captured scene is specified in the spectral image by the spectral reflectance factor. This measurement is independent of the particular illumination of the scene and allows the colorimetric computation in a device-independent colour space for any chosen illuminant and any observer. This thesis describes the project and construction of a compact spectrophotometric camera, which can be used in both portable and in-situ applications. The compactness is made possible by a suitable image spectral scanning based on an Induced Transmission Filter (ITF). This filter is made by a set of thin-film coatings of dielectric materials with high and low refraction index, whose shape like a wedge induces a wavelength selective transmittance, continuously variable along one direction and uniform in the perpendicular direction. Such a filter, classified as Linearly Variable Filter (LVF), operates continuously from 430nm to 940nm and allows hyperspectral imaging. In traditional scanners the whole apparatus is moved along a path as long as the scene, whereas in this instrument the camera body is still and the LVF is the only moving part. The sequence of operations for wavelength and radiometric calibrations are discussed. The expected acquisition times and number of images as a function of the spectral sampling step are considered. The resulting properties make the instrument easy to use and with short acquisition times. Moreover, overviews of the historic evolution of colour vision fundamentals, colour spaces and spectral imaging technology are given for introducing the reader to the essential concepts useful for the understanding of the text

Assessment of multispectral and hyperspectral imaging systems for digitisation of a Russian icon

In a study of multispectral and hyperspectral reflectance imaging, a Round Robin Test assessed the performance of different systems for the spectral digitisation of artworks. A Russian icon, mass-produced in Moscow in 1899, was digitised by ten institutions around Europe. The image quality was assessed by observers, and the reflectance spectra at selected points were reconstructed to characterise the icon’s colourants and to obtain a quantitative estimate of accuracy. The differing spatial resolutions of the systems affected their ability to resolve fine details in the printed pattern. There was a surprisingly wide variation in the quality of imagery, caused by unwanted reflections from both glossy painted and metallic gold areas of the icon’s surface. Specular reflection also degraded the accuracy of the reconstructed reflectance spectrum in some places, indicating the importance of control over the illumination geometry. Some devices that gave excellent results for matte colour charts proved to have poor performance for this demanding test object. There is a need for adoption of standards for digitising cultural heritage objects to achieve greater consistency of system performance and image quality.This article arose out of a Short-Term Scientific Mission (STSM) conducted by Tatiana Vitorino when visiting University College London during a 2-week period in late October 2015. The research was carried out under the auspices of the European COST Action TD1201 Colour and Space in Cultural Heritage (COSCH). The project website is at http://www.cosch.info. Under the COST rules, TV received funding for travel and accommodation expenses, and all coauthors were able to claim travel expenses to attend the subsequent COSCH project meeting. No other funding was received from COSCH for labour or equipment and all work was done on a voluntary pro bono basis.info:eu-repo/semantics/publishedVersio

KNOWLEDGE AND DOCUMENTATION OF RENAISSANCE WORKS OF ART: THE REPLICA OF THE “ANNUNCIATION” BY BEATO ANGELICO

The Annunciation by Guido di Pietro from Mugello, known as Beato Angelico, is a wide tempera painting with some fine gold foil placed on a wooden support, today hosted at the Museum of the Basilica of Santa Maria delle Grazie, in San Giovanni Valdarno. On the occasion of the exhibition “Masaccio e Angelico. Dialogo sulla verità nella pittura”, the museum asked to the Department of Architecture at the University of Bologna to develop a digital high-resolution surrogate to favour deep investigations, to plan restoration and to simply tell the stories behind the artwork. Two tasks were accomplished: to let visitors discover the secrets in the painting and to let scholars study the artwork, to better understand the masterpiece. This paper introduces the outcomes of the research developed to digitize the Annunciation, following a dedicated pipeline developed to improve the fruition of its digital replica, originated from different input sources, and surrogating the user experience on the real object. This work presents a method for the 3D reconstruction of the surfaces based on different techniques for elements with different depth resolutions (i.e., the painting and the wooden frame) which combine photogrammetry and photometric stereo exploiting both procedures and pushing forward the boundaries of Gigapixel Imaging and photogrammetric-based 3D model representation

A compact spectral camera for VIS-NIR imaging

This paper describes the design of a spectro-photo/radio-metric camera, that can be used in both portable and in-situ applications, whose compactness is made possible by a suitable image spectral scanning scheme based on a Linearly Variable Filter (LVF). Such filter is able to operate continuously from 400 nm to 2500 nm, allowing the hyper-spectral imaging from visible to near infrared. In traditional scanners the whole apparatus is moved along a path as long as the scene, whereas in this instrument the camera body is still and the LVF it is the only moving part. This solution allows a compact design and an easily portable instrument

Colour-Difference Assessment for Driving Headlight Simulation

In high quality driving simulation applications, such as headlight simulation, colorimetric validity is essential. In virtual testing of headlight systems, it is important that the WYSIWYG (What You See Is What You Get) paradigm is respected for product quality headlight assessment. Indeed, if a slightly reddish orange colour is displayed instead of the typical orange of halogen lighting, the effect for driver comfort or traffic safety can be critical. The lighting specialist should accept a headlight which doesn't have the right colour. Previous studies have shown that there is a significant colour difference between virtual and real environments. Nevertheless, in virtual headlight testing the rendered colour fidelity has to fit industrial assessment. This study therefore deals with the colour-difference perceptibility that is the ability of an observer to detect a difference between two colours and, more precisely, on the acceptability of the perceived difference. We propose in this paper a psychophysical function for colour difference acceptability which fits well with the measured data. The colour acceptability function was implemented in a driving simulator for high validity headlight assessment. Driver acceptability experimentation was carried out using Renault's headlight driving simulation equipped with a fullcab and a 210° cylindrical display screen

Color-difference assessment and enhancement for driving headlight simulation

Real-time headlight simulation in driving conditions is used by most car manufacturers to assure the quality, cost, and delivery of headlight engineering design. An important parameter judged by the headlight assessment team is color restitution; indeed, this parameter has to meet the standard of “lamps for road vehicles.” Therefore, the goal of this study was the color assessment and enhancement of a driving headlight simulator. For this purpose, this study was conducted in two phases: the process of constructing two color acceptability scales that directly reflect the perception of two different populations (experts and “naive”), and the assessment of a method based on the chromatic adaptation transform (CAT) for reducing the color difference between real and virtual environments. In the first phase, we conducted two psychophysical experiments (i.e., one for each population), in which the observers had to report their degree of satisfaction about the color difference. These two experiments enabled the creation of two acceptability scales for headlight simulation. In the second phase, we compared the performance of different chromatic transformations; as a result of this comparison, we advise the use of the CAT02 transformation, in order to reduce the color difference for headlight assessment in driving simulation experiments.ANRT (Association Nationale de la Recherche et de la Technologie) and Renaul

Design and Construction of a Multispectral Camera for Spectral and Colorimetric Reproduction

Multi-spectral imaging and spectral reflectance reconstruction can be used in cultural-heritage institutes to digitalize their collections for documentation purposes. It can be used to simulate artwork under any lighting condition, and to analyze colorants that were used. The basic idea of a multi-spectral imaging system is to sub-sample spectral reflectance factor, producing results similar to a spectrophotometer. The sampled data are used to reconstruct reflectance for the visible spectrum. In this thesis, a wide band multispectral camera was designed and constructed to achieve high spectral and color accuracy as well as high image quality. Noise propagation theory was introduced and tested. A seven channel band- pass filter set was modeled using Gaussian functions and optimized to yield high spectral and colorimetric reproduction accuracy as well as low colori- metric noise. Single and sandwich filters were selected from o!-the-shelf absorption filters using the Gaussian bandpass filter model. Experiments were conducted to test the spectral, color and noise performance of the novel sandwich filters and compared with interference filters. The novel sandwich fil- ters led to increased colorimetric accuracy along with a reduction colorimetric noise. This imaging system will be used as part of a recommended workflow for museum archiving, and will be an important addition to the spectral imaging capabilities at MCSL