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(a) Normalised intensity measured through the 880nm filter as a function of angle between the normal of the target surface and the optical axis of the camera at a distance of ∼7m for the matte Spectralon white standard; (b) a comparison of the angular dependence of the reflected intensity of light at 880nm for different colour patches on a mock wall painting tile (picture shown in Fig. 10a) and the Spectralon white standard. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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PRISMS (Portable Remote Imaging System for Multispectral Scanning) is designed for in situ, simultaneous high resolution spectral and 3D topographic imaging of wall paintings and other large surfaces. In particular, it can image at transverse resolutions of tens of microns remotely from distances of tens of metres, making high resolution imaging po...
Citations
... The photogrammetric procedure can be modified by changing the light conditions from the normal process, which allows the definition of spectral photogrammetry. This approach was applied by the group of Mathys et al. [5], which focused on the digitization of biological objects with predominantly reflective surfaces [6,7]. The digitization of these objects was performed using two cameras that captured different wavelengths of the visible spectrum, as well as infrared and ultraviolet radiation, using different polarization filters for each wavelength. ...
The increasing demand for accurate and detailed 3D modeling in fields such as cultural heritage preservation, industrial inspection, and scientific research necessitates advanced techniques to enhance model quality. This paper addresses this necessity by incorporating spectral imaging data to improve the surface detail and reflectivity of 3D models. The methodology integrates spectral imaging with traditional 3D modeling processes, offering a novel approach to capturing fine textures and subtle surface variations. The experimental results of this paper underscore the advantages of incorporating spectral imaging data in the creation of 3D models, particularly in terms of enhancing surface detail and reflectivity. The achieved experimental results demonstrate that 3D models generated with spectral imaging data exhibit significant improvements in surface detail and accuracy, particularly for objects with intricate surface patterns. These findings highlight the potential of spectral imaging in enhancing 3D model quality. This approach offers significant advancements in 3D modeling, contributing to more precise and reliable representations of complex surfaces.
... Indeed, even though there are works exploiting X-ray as radiation to perform stratigraphic studies [27,[45][46][47][48][49][50][51], MA-XRF has never been devoted to the determination of layer thickness. Indeed, other methods can be used for 3D topography when given conditions are present [52][53][54]. The present work aims at studying the thickness distribution of a pigment layer over a lead white support through XRF mapping. ...
Even though X-ray fluorescence (XRF) is strictly an atomic method, this technique has been developed mostly at research centers for nuclear physics. One of its most valuable variations is the mapping mode that allows it to shift XRF from a punctual to an image technique. Macro X-ray Fluorescence (MA-XRF) is a widespread analytical technique applied in cultural heritage for characterizing the elemental composition of pigments with a non-destructive, rapid and green approach. When dealing with cultural heritage materials, the sustainability of the applied techniques is directly linked to the limited impact on the work of art. MA-XRF can reveal hidden sub-surface layers or restorations, but, nonetheless, it is hardly adopted for estimating the thickness of layers without resorting to complex Monte Carlo simulations or without combining information from other techniques. Exploiting the recurrent presence of lead white under pictorial layers in historical artworks, we perform a calibration on stand-alone layers produced ad hoc for the relative absorption of Pb L fluorescence lines, and then, their ratio is successfully used to estimate the thickness of azurite and ultramarine blue layers over lead white. The final result is rendered as a heatmap, easy to present to non-technical personnel frequently involved in the cultural heritage field. The new proposed procedure for calculating layer thickness extends the concept of non-invasive applications, paving the way to the possibility of performing stratigraphy without sampling.
... The practice of 3D digitization is now commonly used in museum settings for study [Hassett 2017], Preservation [Lopez-Martinez 2018], and dissemination [Gonizzi 2013] purposes. The use of spectral and 3D imaging in conjunction for cultural assets has recently been the subject of more and more efforts, such as highlighting features [Webb 2017], recognising substances [Liang 2014], documenting the wavelength of light reflected by the object [Kim 2012], and generating a more precise representation of the object's colors [Brusco 2016], evaluating the state of preservation or decay [Simon 2013]. ...
In recent years, close-range photogrammetric scanning systems have become increasingly popular due to their low-cost hardware, components, and user-friendly software. These systems utilize high-resolution cameras and advanced algorithms to produce accurate and precise 3D models, which are essential for analyzing, documenting, and preserving cultural heritage. While there are various methods for creating 3D models, minimizing cost and time is a primary concern. This paper focuses on photogrammetry as an option for surface reconstruction that might be used to make 3D representations of transparent objects. The objective of the research is to investigate the feasibility of creating appropriate 3D models for surface reconstruction and units of transparent objects through photogrammetry, utilizing open-source photogrammetry algorithms.
... Numerous researchers have crafted spectral 3D models with the aim of enhancing the accuracy and dependability of computer vision tasks across diverse applications. These applications encompass areas like plant modeling [2], agriculture surveillance [3], preservation of digital cultural heritage [4], and material classification [5]. ...
p>Spec-NeRF jointly optimizes the degradation parameters and achieves high-quality multi-spectral image reconstruction results at novel views, which only requires a low-cost camera (like a phone camera but in RAW mode) and several off-the-shelf color filters. We also provide real scenarios and synthetic datasets for related studies. Code is available at https://github.com/CPREgroup/SpecNeRF-v2 </p
... Numerous researchers have crafted spectral 3D models with the aim of enhancing the accuracy and dependability of computer vision tasks across diverse applications. These applications encompass areas like plant modeling [2], agriculture surveillance [3], preservation of digital cultural heritage [4], and material classification [5]. ...
p>Spec-NeRF jointly optimizes the degradation parameters and achieves high-quality multi-spectral image reconstruction results at novel views, which only requires a low-cost camera (like a phone camera but in RAW mode) and several off-the-shelf color filters. We also provide real scenarios and synthetic datasets for related studies. Code is available at https://github.com/CPREgroup/SpecNeRF-v2 </p
... Non-ionising radiation makes these techniques non-invasive. Standalone optical imaging for cultural heritage applications includes several techniques which are contactless and remote-sensing, which broadly range from more conventional methods (digital and multi-band photography) [4], to imaging spectroscopy techniques (multispectral and hyperspectral imaging) [5][6][7][8], and the 2D/3D methods of cultural heritage digitisation [9][10][11][12][13]. All these techniques feature high versatility and operate in imaging mode; crucial whenever the task is the examination of the gurative arts. ...
This study provides new data which suggests a novel interpretative hypothesis not only on the specific painting, but on the use of bloodletting as medical practice in the Florentine Quattrocento. In addition, the technical solutions adopted to implement the measurements campaign are illustrated as an experimental model for remote sensing investigations of paintings studied in situ.
The position of the painting high up on a wall of an historical venue led to opting for standalone optical imaging techniques which could operate in remote sensing mode. By combining the use of portable Hyperspectral Imaging with Near Infrared photography a set of detailed images could be obtained that highlighted details not otherwise detectable. Focused on the objects held by the persons present, the analysis of the mural of Visit of the Buonomini in her Lying in Bed, the gift of swaddling cloth could be a tourniquet, shadows of folds of a blanket a thumb lancet, and an object held a blood collection bowl, supported the hypothesis that it could be a medieval bloodletting scene.
... Consider the recent bibliography of Elkhuizen et al on 3D techniques with 16 articles, which in fact is limited to 11 [44][45][46][47][48][49][50][51][52][53][54]. According to our research, this appears to be a state of the art with only the reference [55] added. This number is small compared to the consequent number of publications devoted to the image analysis of artistic paintings. ...
Identification of an individual artist’s touch on paintings is studied using surface metrology. Paintings’ topographies were measured using focus variation and stitching, creating 13 × 13 mm maps with 1 μm sampling intervals, and 169 megapixels, with a 10X objective lens. Topographic characterization parameters were analyzed for their ability to differentiate different painters’ renderings. Statistical treatments from data mining were used to discriminate, by optimization, multiscale topographic signatures characterized by a multitude of areal texture parameters. It appears that a fractal dimension can define 3 characteristic scale ranges. One from 3 to 70 μm corresponds to brushstroke details. Another, from 70 to 700 μm, corresponds to the topography of the material of the canvas fabric. Finally, scales greater than 700 μm correspond to undulations of the canvas. For scales less than 50 μm, the fractal structure of the topography left by brushstrokes follows a power law characterized by the slopes of the topography. The topography of the clouds painted on the canvas has an Sdq (topographic slopes) increasing with the clarity of the clouds at scales of 3–500 μm. According to the Torrance-Sparrow theory, the higher the Sdq, the more diffuse the light on the surface. The painter therefore wanted to show, by his brushstroke, that the light clouds diffuse more light giving an impression of local brightness. This study is confirmed by the analysis of the painting of Max Savy, a French painter from Carcassonne (1918–2009), which was measured with a white light interferometer Zygo NewView 7300, a X100 objective lens giving a 517 μm × 517 μm stitched surface, with a sampling interval of 0.109 μm. The box-counting method for estimating the fractal dimension of the topography of an oil painting appears optimal by the fact that it morphologically integrates scale variations of the local slopes of the surface morphology. This method thus characterizes the multiscale aspects, as well as the scale changes, of the topography.
... Presently, mainly specialized instruments are used to carry out spectral imaging. Many systems that have been developed for lab-based research or in situ field studies are experimental [5][6][7]. They are typically applied in one-off technical studies, and are not intended or appropriate for adoption within routine imaging workflows. ...
A portable, user-friendly multispectral imaging system assembled almost entirely of common photography equipment and open-source software has been developed. The system serves as an outreach and educational tool for demonstrating and promoting scientific imaging as a more routine practice in the contexts of cultural heritage digitization and photography. These efforts are aimed primarily at institutions where advanced imaging technologies are not already found, and where funding and expertise may limit access to commercial, bespoke multispectral imaging solutions that are currently available. The background and theory that were shared in tutorials given during the system’s initial testing campaign are detailed here. Testing was carried out in one-day on-site visits to six cooperating institutions of different sizes and collection types in the northeast USA. During these visits, the imaging system was presented, and the benefit of collecting spectral data using low barrier-to-entry capture and processing methods relative to conventional imaging methods was discussed. Imaging was conducted on site on selected collections objects to showcase the current capabilities of the system and to inform ongoing improvements to the setup and processing. This paper is a written companion piece to the visits, as a source of further detail and context for the two-light imaging system that was described and demonstrated.
... As spectral imaging systems have limitations, such as short ranges, they are not the first choice for non-movable, large-sized murals, especially when they are located inside or outside monuments and require dedicated artificial illumination systems. In such cases, remote-sensing hyperspectral imaging is used instead [39,40]. However, the present case study of a large-scale monument with stone surfaces pioneered the application of the methods on non-conventional materials, and in the end obtained remarkable results. ...
The paper contributes new information about the Horologion of Andronikos Kyrristos of the Roman Agora of Athens, Greece and its continuous presence in Athens from antiquity until now. The monument is of cultural, historical and astronomical importance. It has undergone conservation work and non-destructive documentation which contribute to its sustainability. The spectral imaging technique, which allows the acquisition of high-resolution images, was applied on the stone surfaces of the monument. The acquisition of images in the visible and infrared regions, combined with the digital tracing reproduction of the graffiti and image processing, is used for the first time in this particularly interesting case study of the aforementioned monument, of which a complete description is provided. New evidence with a clearer recording of the vessels already mentioned in the literature, as well as the detection of new historical data and graffiti, is discussed in comparison with the results of previous studies.
... The method is easily applied to the study of polychrome surfaces of small-or medium-size objects in museum collections, as easel paintings, illuminated manuscripts or paper-based artefacts. More recently, it has been applied also outdoor on large mural surfaces [17][18][19] and archaeological sites, with the aid of avionic-based spectral cameras originally developed for earth-surface observations [20]. ...
... [9,10,13,20]) and (ii) a filter-based imaging system (see, e.g. [8,17,23,24]). The first approach produces the spectral datacube line-byline by moving the object or the detector over one spatial coordinate: for each scanning step, the object surface is illuminated in a narrow strip and the scattered or emitted light is collected through a slit. ...
... To solve this issue, Balas and co-authors [26] have recently developed a spectral scanning camera based on the use of a tuneable electro-optic filter that produces a spectral datacube covering the entire 370-1100 nm spectral range with a variable spectral resolution ranging from 6 to 12 nm in a few tens of seconds. In contrast to line scanning, the method has the advantage of being easily coupled to different optical systems in collection, allowing it to be used to study surfaces of variable sizes, from microscale [27,28] to large surfaces [8,23,24,29], and placed at variable distances [17]. ...
Scientific investigation in the cultural heritage field is generally aimed at the characterization of the constituent materials and the conservation status of artworks. Since the 1990s, reflectance spectral imaging proved able to map pigments, reveal hidden details and evaluate the presence of restorations in paintings. Over the past two decades, hyperspectral imaging has further improved our understanding of paints and of its changes in time. In this work, we present an innovative hyperspectral camera, based on the Fourier transform approach, utilising an ultra-stable interferometer and we describe its advantages and drawbacks with respect to the commonly used line- and spectral-scanning methods. To mitigate the weaknesses of the Fourier transform hyperspectral imaging, we propose a strategy based on the virtual extension of the dynamic range of the camera and on the design of an illumination system with a balanced emission throughout the spectral range of interest. The hyperspectral camera was employed for the analysis of a painting from the “Album of Nasir al-din Shah”. By applying analysis routines based on supervised spectral unmixing, we demonstrate the effectiveness of our camera for pigment mapping. This work shows how the proposed hyperspectral imaging camera based on the Fourier transform is a promising technique for robust and compact in situ investigation of artistic objects in conditions compatible with museum and archaeological sites.
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