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A New Camera for High-Resolution Infrared Imaging of Works of Art
Abstract
A new camera - SIRIS (scanning infrared imaging system) - developed at the National Gallery in London, UK allows highresolution images to be made in the near infrared region (900-1700 nm). The camera is based on a commercially available 320 × 256 pixel indium gallium arsenide area array sensor. This relatively small sensor is moved across the focal plane of the camera using two orthogonal translation stages to give images of c. 5000 × 5000 pixels. The main advantages of the SIRIS camera over scanning infrared devices or sequential image capture and mosaic assembly are its comparative portability and rapid image acquisition - making a 5000 × 5000 pixel image takes less than 20 minutes. The SIRIS camera can operate at a range of resolutions, from around 2.5 pixels per millimetre over an area of up to 2 × 2 m to 10 pixels per millimetre when examining an area measuring 0.5 × 0.5 m. The development of the mechanical, optical and electronic components of the camera, including the design of a new lens, is described. The software used to control image capture and to assemble the individual frames into a seamless mosaic image is mentioned. The camera was designed primarily to examine underdrawings in paintings; preliminary results from test targets and paintings imaged in situ are presented and the quality of the images compared with those from other cameras currently used for this application.
... 124). The spectral sensitivity of the Osiris, which is equipped with an InGaAs sensor, is stated to range between 900 and 1700 nm [28]. Novel transmission measurements by Geffken and Dittmar could prove, that the Osiris camera is already sensitive for lower wavelength area even though to a considerably lesser extent [23] (p. ...
... No. HM 6, Inv. No. HM 15) were performed with an Osiris-A1 camera 4 [28], IRR of "Virgin and Child" by Cima da Conegliano (Inv. No. 852) with a vidicon tube system [33,34]. ...
... 5 Conventional IRR with a broad range of wavelengths using halogen-based Hedler ® HT 19 s lights as excitation source were already existent. 6 [28]. 5 Hamamatsu Infrared Vidicon Camera C2741-03. ...
Until today, iron gall ink is classified as an exceptional underdrawing material for paintings. Its study and definite identification is usually based on invasive analysis. This article presents a new non-destructive approach using micro-X-ray fluorescence scanning (MA-XRF), LED-excited IRR (LEDE-IRR) based on a narrow wavelength-range of infrared radiation (IR) for illumination and stereomicroscopy for studying and visualising iron gall ink underdrawings. To assess possibilities and limits of these analytical techniques, the approach was tested on panel paintings by Hans Holbein the Elder and Giovanni Battista Cima da Conegliano. Results are compared to invasive examinations on cross-sections using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). The holistic setup could successfully visualise iron gall ink underdrawings, allowing to harness the formerly invisible underdrawing lines for interdisciplinary studies.
... A plethora of imaging techniques have been developed and employed for inspecting a number of CH items. Although a comprehensive review is out of the scope of this work, Table 1 shows details of references [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], highlighting the different nature of the inspected items and the main findings, with a close look on the combination of techniques and tools used. Underdrawings test chart; "The Adoration of the Name of Jesus" by El Greco; "The Virgin and Child with Saints Jerome and Francis" by Perugino. ...
... Acrylic, vinylic, oil media, and enamal paints have been succesfully identified with SR-FTIR, with or without opacifiers. Table 1 shows that the use of a range of imaging techniques and tools can provide an in-depth knowledge of different CH items in a reliable way without the need for sampling micro-chips of materials for laboratory analysis, a fact that is in general highly desirable or even mandatory in some cases [4,6,9,10,[12][13][14][15][16][17][18][19][20]. ...
... Details of references[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. ...
Before starting the restoration of an artwork, good practice involves the evaluation of the item healthiness possibly carried out through non-invasive techniques. In the specific case of painting inspection, hyper-and multi-spectral techniques are commonly used to analyze the outer layers (varnish, pictorial, and drawing), while X-ray, tomography, and many others can be employed to investigate its inner structure. Although highly desirable, a single technique providing all the information about a painting is still not available. Thus, it is of great interest to define the analysis' protocols that could optimally exploit the complementarities of a minimal set of techniques. To this aim, the present paper shows the combined use of the hypercolorimetric multispectral imaging and pulse-compression thermography on a 15th century wall painting attributed to the Italian artist Antonio del Massaro, also known as Pastura, representing the Madonna with the Child and the Saints Jerome and Francis. The capabilities and the complementarities of the two techniques, whose information can also be fused through post-processing, are illustrated in detail in this paper. In addition, a false-colour imaging approach is proposed to improve the readability and analysis of the thermography results.
... Digital scanning back cameras utilizing small IR arrays have been constructed to improve the scan efficiency and enable the camera system to be portable [10,11]. Such examples include the novel sensor constructed at the National Gallery, London. ...
... This IRR camera consists of a custom lens with a large field of view and a small InGaAs area array. The image from the lens is 'scanned' with the small IR area array (256 × 320 pixels) to create a mosaicked 5k by 5k pixel IRR image in ~20 min [10]. A commercial version of this design, the Osiris camera, utilizes a small linear photodiode InGaAs array instead of the area array [11], producing a 4k by 4k pixel IRR image. ...
Background
Infrared reflectography (IRR) remains an important method to visualize underdrawing and compositional changes in paintings. Older IRR camera systems are being replaced with near-infrared cameras consisting of room temperature infrared detector arrays made out of indium gallium arsenide (InGaAs) that operate over the spectral range of ~900 to 1700 nm. Two camera types are becoming prevalent. The first is staring array infrared cameras having 0.25–1 Megapixels where the camera or painting is moved to acquire tens of individual images that are later mosaicked together to create the infrared reflectogram. The second camera type is scanning back cameras in which a small InGaAs array (linear or area array) is mechanically scanned over a large image formed by the camera lens to create the reflectogram, typically 16 Megapixels. Both systems have advantages and disadvantages. The staring IR array cameras offer more flexible collection formats, provide live images, and allow for the use of spectral bandpass filters that can provide reflectograms with better contrast in some cases. They do require a mechanical system for moving the camera or the artwork and post-capture image mosaicking. Scanning back cameras eliminate or reduce the amount of mosaicking and movement of the camera, however the need to minimize light exposure to the artwork requires short integration times, and thus limits the use of spectral bandpass filters. In general, InGaAs cameras are not sensitive in the 1700 to ~2300 nm spectral region, which has been identified in prior studies as useful for examining paintings with copper green pigments or thick lead white paints. Prior studies using cameras with sensitivity from 1000 to 2500 nm have found in general the performance at wavelengths longer than 1700 nm degraded relative to the performance at shorter wavelengths. Thus, there is interest in a camera system having improved performance out to 2500 nm that can utilize spectral bandpass filters.
Methods
Design requirements for such an improved IRR camera system were determined by first re-examining the optimal spectral window for detecting underdrawing. Thus the wavelength dependence of the clarity of carbon black underdrawings on a chalk ground covered by various paint swatches was measured from 750 to 2500 nm. Second, analysis of the loss of light transmission (1000–2500 nm) and the impact of thermal radiation (3000–5000 nm) on the performance of IR arrays sensitive to the 1000–5000 nm region was analyzed. From the results of these studies, a high sensitivity, near-infrared (1000–2450 nm) indium antimonide (InSb) staring array camera with a cold filter that blocked light >2450 nm was constructed with a color-corrected macro lens capable of holding interference filters. The camera system was characterized in three spectral bands (1100–1400, 1500–1800, and 2100–2400 nm) using test targets and art objects.
Results
The experimental results of the contrast difference between the model underdrawing on the chalk ground showed the optimal spectral window for a given pigment varied over the range from 700 to 2300 nm. The contrast in all cases was found to be low from 2300 to 2600 nm and even lower from 2600 to 5000 nm. This is attributable in part to broad absorption by the drying oil paint binder. Performance testing of the IRR camera found high signal-to-noise was observed in all three spectral bands due to the optimized macro lens having high transmission from 1000 to 2600 nm, a 100% efficiency cold stop, and a cold filter that blocks light >2450 nm. The camera was found to have high light sensitivity, requiring only ~30 to 50 lx from incandescent lamps having a color temperature of ~2060 K. The images produced in each spectral band were sharp, and the modulation at Nyquist (1/2 the sampling frequency) was 20%. IRR images of Old Master paintings, works on paper, and a warped panel painting were collected to test the practical utility of the camera system.
Conclusions
The IR camera system presented here was found to produce a variety of high-resolution image products. The ability to extend image collection over the 1700–2450 nm spectral range was found in some examples to provide improved visibility of underdrawing. The ability to register the resulting multi-band IRR images with the color image offers opportunities to produce new image products such as false-color images and principal component images. These image products were found to give new insights into the construction of works of art. A collection scheme based on a ‘Z-stack’ method was found to solve the problem of producing high-resolution IRR images of highly warped panel paintings.
... In fact, only high resolution reflectograms can properly visualize all the features of the underdrawing such as shading, thin brush strokes and lines that can be thinner than 200 lm. In the past years many scanning system have been proposed [13][14][15][16][17][18] and some are currently working with excellent results [19][20][21]. Although these devices present many advantages, they have also some drawbacks http://dx.doi.org/10.1016/j.infrared.2016.12.011 1350-4495/Ó 2016 Elsevier B.V. All rights reserved. ...
... All the Single Photodiode Scanners (SPS) belong to the first category: they scan the entire painting surface with a single pin-photodiode detector that has an appropriate focusing system [13,17,18]. The Image Plane Scanner (IPS) [14,15,20] and the Moving Lens Scanner (MLS) [16] belong to the second category. This paper describes the working principle, the realization and the testing of an innovative device, extremely portable and high performing, able to achieve high resolution reflectograms. ...
Infrared reflectography is an imaging technique used to visualize the underdrawings of ancient paintings; it relies on the fact that most pigment layers are quite transparent to infrared radiation in the spectral band between 0.8 μm and 2.5 μm. InGaAs sensor cameras are nowadays the most used devices to visualize the underdrawings but due to the small size of the detectors, these cameras are usually mounted on scanning systems to record high resolution reflectograms. This work describes a portable scanning system prototype based on a peculiar spherical scanning system built through a light weight and low cost motorized head. The motorized head was built with the purpose of allowing the refocusing adjustment needed to compensate the variable camera-painting distance during the rotation of the camera. The prototype has been tested first in laboratory and then in-situ for the Giotto panel “God the Father with Angels” with a 256 pixel per inch resolution. The system performance is comparable with that of other reflectographic devices with the advantage of extending the scanned area up to 1 m x 1 m, with a 40 minutes scanning time. The present configuration can be easily modified to increase the resolution up to 560 pixels per inch or to extend the scanned area up to 2 m x 2 m.
... IRR was introduced in the 1960's by J.R.J. van Asperen de Boer, using PbS-based Vidicon tubes as recording devices and has seen important technological improvements over the past years [33][34][35]. An infra-red (IR) source of around 1.2 μm is used to illuminate objects; this radiation will readily penetrate through a number of commonly occurring paint constituents such as lead white, while becoming strongly absorbed by others such as carbon black. ...
... Next to the acquisition of full field reflection images by IR-sensitive cameras, scanning may also be employed. Already in 2006, Saunders et al. [35] devised a camera system that acquired 25 Mpixel IRRs with a lateral resolution of 100 μm; it incorporated a small (320 × 256 pixel) moving InGaAs sensor of which the images were stitched together. This lightweight camera, suitable for in-situ measurements, is commercially available (OSIRIS camera) and is sensitive in the 0.9-1.7 μm wavelength range. ...
The development of advanced methods for non-destructive selective imaging of painted works of art at the macroscopic level based on radiation in the X-ray and infrared range of the electromagnetic spectrum are concisely reviewed. Such methods allow to either record depth-selective, element-selective or species-selective images of entire paintings. Camera-based ‘full field’ methods (that record the image data in parallel) can be discerned next to scanning methods (that build up distributions in a sequential manner by scanning a beam of radiation over the surface of an artefact). Six methods are discussed: on the one hand, macroscopic X-ray fluorescence and X-ray diffraction imaging and X-ray laminography and on the other hand macroscopic Mid and Near Infrared hyper- and full spectral imaging and Optical Coherence Tomography. These methods can be considered to be improved versions of the well-established imaging methods employed worldwide for examination of paintings, i.e., X-ray radiography and Infrared reflectography. Possibilities and limitations of these new imaging techniques are outlined.
... The role of photography in today's art scene has become a topic of undeniable importance for theorists and artists alike (Price, 2021) (Batchen, 2020) ( Krauss, 1986). While acknowledging the frequent use of cameras for art documentation (Saunders et al., 2006), this investigation argues for the unique qualities of photography, especially in the digital age. Today, countless artists utilize the camera to achieve their artistic visions. ...
... µm wavelengths, though there are devices exploiting wavelengths in the 1.5-3 µm range. Both IRR and IRP use an incandescent lamp, such as a halogen float lamp of 1000 W, or a quantum source, such as a light-emitting diode (LED) or laser, as a primary source and record the reflected radiation by means of a camera equipped with an infrared film (IRP) or a sensor sensitive to the infrared part of the spectrum (IRR) and an infrared cut-off filter [2,5,31]. The latter absorbs visible light and lets the infrared radiation pass. ...
Applications of non-invasive sensing techniques to investigate the internal structure and surface of precious and delicate objects represent a very important and consolidated research field in the scientific domain of cultural heritage knowledge and conservation. The present article is the first of three reviews focused on contact and non-contact imaging techniques applied to surveying cultural heritage at micro- (i.e., manufacts), meso- (sites) and macro-scales (landscapes). The capability to
infer variations in geometrical and physical properties across the inspected surfaces or volumes is the unifying factor of these techniques, allowing scientists to discover new historical sites or to image their spatial extent and material features at different scales, from landscape to artifact. This first part concentrates on the micro-scale, i.e., inspection, study and characterization of small objects (ancient papers, paintings, statues, archaeological findings, architectural elements, etc.) from surface
to internal properties.
... Each of these have advantages and drawbacks in terms of cost, scanning area, scan time, and spectral resolution. Scanning can rely on single-pixel systems [17,18] or image plane systems [18][19][20][21], some operating with a multispectral approach [4,21-25] and others integrating 3D information [26]. The instrument presented here, of the second type, was developed as the evolution of a former prototype with the specific aim to address a series of observed issues [27]. ...
Since infrared reflectography was first applied in the 1960s to visualize the underdrawings of ancient paintings, several devices and scanning techniques were successfully proposed both as prototypes and commercial instruments. In fact, because of the sensors’ small dimension, typically ranging from 0.1 to 0.3 megapixels, scanning is always required. Point, line, and image scanners are all viable options to obtain an infrared image of the painting with adequate spatial resolution. This paper presents a newly developed, tailormade scanning system based on an InGaAs camera equipped with a catadioptric long-focus lens in a fixed position, enabling all movements to occur by means of a rotating mirror and precision step motors. Given the specific design of this system, as the mirror rotates, refocus of the lens is necessary and it is made possible by an autofocus system involving a laser distance meter and a motorized lens. The system proved to be lightweight, low cost, easily portable, and suitable for the examination of large-scale painting surfaces by providing high-resolution reflectograms. Furthermore, high-resolution images at different wavelengths can be obtained using band-pass filters. The in-situ analysis of a 16th-century panel painting is also discussed as a representative case study to demonstrate the effectiveness and reliability of the system described herein.
... A common (and powerful) approach to the problem is the use of multi/hyper-spectral imaging techniques [7,8], which have been developed in the last decades following technological advances in digital photography and landscape surveying [9]. However, in most cases, multi/hyper-spectral methods are used for the identification of the pigments in the painting [10][11][12][13] and/or studying the underdrawings through infrared imaging [14][15][16][17][18][19]; less frequent are the studies aimed at the recovery of the legibility of the images. Important works have been done in the past decade towards the recovery of the visibility of degraded manuscripts [20][21][22][23] but some effort has also been devoted to ancient mural paintings, one noteworthy example being the development of the DStretch ® software [24] and its application to rock [25] and wall [26] paintings. ...
In this paper, we discuss a new approach to the analysis of multi/hyper-spectral data sets, based on the Interesting Features Finder (IFF) method. The IFF is a simple algorithm recently proposed in the framework of Laser-Induced Breakdown Spectroscopy (LIBS) spectral analysis for detecting ‘interesting’ spectral features independently of the variance they represent in a set of spectra. To test the usefulness of this method to multispectral analysis, we show in this paper the results of its application on the recovery of a ‘lost’ painting from the Etruscan hypogeal tomb of the Volumni (3rd century BCE—1st century CE) in Perugia, Italy. The results obtained applying the IFF algorithm are compared with the results obtained by applying Blind Source Separation (BSS) techniques and Self-Organized Maps (SOM) to a multispectral set of 17 fluorescence and reflection images. From this comparison emerges the possibility of using the IFF algorithm to obtain rapidly and simultaneously, by varying a single parameter in a range from 0 to 1, several sets of elaborated images all containing the ‘interesting’ features and carrying information comparable to what could have been obtained by BSS and SOM, respectively.
... Modern customized digital "NIR" cameras can obtain images with a wavelength in the near infra-red (800nm -2000nm wavelength) with a reasonable resolution [Saunders et al., 2006;Ribés et al., 2005]. Often it happens that with infra-red we identify not only under drawing or "pentimenti", but also signatures, dates, and inscriptions or monograms that help in the characterization of the artwork. ...
The role of museums and libraries is shifting from that of an institution which mainly collects and stores artefacts and works of art towards a more accessible place where visitors can experience heritage and find cultural knowledge in more engaging and interactive ways. Due to this shift, ICT have an important role to play both in assisting in the documentation and preservation of information, by providing images and 3D models about historical artefacts and works of art, and in creating interactive ways to inform the general public of the significance that these objects have for humanity. The process of building a 3D collection draws on many different technologies and digital sources. From the perspective of the ICT professional, technologies such as photogrammetry, scanning, modelling, visualisation, and interaction techniques must be used jointly. Furthermore, data exchange formats become essential to ensure that the digital sources are seamlessly integrated. This PhD thesis aims to address the documentation of works of art by proposing a methodology for the acquisition, processing, and documentation of heritage objects and archaeological sites using 3D information. The main challenge is to convey the importance of 3D model that is "fit for purpose" and that is created with a specific function in mind (i.e. very high definition and accurate models for : academic studies, monitoring conservation conditions over time and preliminary studies for restoration; medium resolution for on-line web catalogues). Hence, this PhD thesis investigate the integration of technologies for 3D capture, processing, integration between different sources, semantic organization of meta-data, and preservation of data provenance.
... This has limited the attempt to extend in the middle IR band for the underdrawings' visualization by means of a short-wave thermal camera with passive technique [10]. In this context, in the last 30 years, most efforts have been devoted to improving both spatial resolution of IR images [11] and portability of SWIR instrumentation [12] for the application on wall paintings. In this way, the techniques have become more and more routinely and essentially oriented to the needs of scholars and art historians for the best underdrawing detection and representation. ...
Reflectographic analyses applied on paintings can be performed using cameras equipped with different detectors with different abilities in detecting and visualizing underdrawings, repainting, restorations, and other nonvisible information. In this research, the results obtained through thermographic imaging followed by statistical imaging postprocessing methods have been compared with those obtained with traditional reflectographic methods in the short-wave infrared range. The comparison has been performed studying the thermal sequence after a single pulse of light with a different spectrum of ad hoc mock-ups. Results showed that for limited cases, signal-to-noise ratio seems to be more relevant in obtaining reliable images of underdrawings with respect to the effect of optical absorption of visible light by painting layers.
... The diagnostic investigation of cultural heritage objects, through non-destructive and non-invasive techniques has become widely applied, due to the development of imaging methods that could supply information useful for conservators to choose the most appropriate intervention decision during a HERITECH 2020 IOP Conf. Series: Materials Science and Engineering 949 (2020) 012008 IOP Publishing doi: 10.1088/1757-899X/949/1/012008 2 restoration work [1][2][3][4][5][6][7][8][9][10]. The non-invasive imaging techniques are fundamental for obtaining a complete knowledge of the surfaces, for addressing the possible sampling of micro-chips of materials for laboratory analysis, and in case of impossibility to take samples from the investigated artworks [11][12][13][14][15][16]. ...
This contribution focuses the attention on an innovative approach in diagnostics of paintings, based on the combine use of two imaging techniques named Hypecolorimetric Multispectral Imaging (HMI) and Pulse Compression Thermography (PuCT) applied to a 15 th century wall painting, attributed to the Italian artist Antonio del Massaro, also known as Pastura. HMI technique is based on the simultaneous exploitation of the electromagnetic spectrum from the ultraviolet to the near infrared region. The acquisition, made under a standard metric, allows for characterizing the investigated surfaces in a more detailed way than the standard colorimetry. The system transforms any spectra in the range 300-1000nm into sevenfold hypecolorimetric coordinates. HMI guarantees very high radiometric (better than 95%) and colorimetric precision (better than ΔE = 2). PuCT is a thermography technique based on the use of coded modulated heating stimuli in combination with the pulse-compression technique. A PuCT scheme, based on coded LED excitation capable of optimizing the estimation of the impulse responses compared to the state-of-the-art PuCT literature has also been proposed. The combined use of HMI and PuCT recently revealed its potentiality in the investigation of important panel paintings by highlighting hidden details, mapping the conservation status, characterizing painting materials, etc. in a completely non-invasive way. Their combined capabilities are here tested on a wall painting representing the Madonna with the Child and the Saints Jerome and Francis, which was investigated during the restoration in the Laboratory in order to supply information about the materials and techniques.
... Infrared reflectography (IRR) is most frequently used in museum contexts to reveal hidden features or preliminary drawings beneath painted surfaces [6]. Carbon is extremely opaque to IR radiation and this technique is therefore particularly useful where such sketches are likely to have been made in a carbon-based medium, as would be expected for a painting of this type. ...
The painting of Death of the Buddha (1913,0501,0.40)
has probably never been on display at the British Museum since
it was acquired in 1913 due to its poor condition at that time. This
fifteenth-century Buddhist painting was recently fully conserved
and remounted as a hanging scroll. What is known of the painting’s
history is explained and its condition before treatment is described
as background to a full account of the entire treatment process. The
successful conservation and mounting of a complex painting on
silk as a hanging scroll requires a great number of treatment stages,
each involving hundreds of careful steps. The overall procedure is
here dealt with in three categories: conservation, mounting and the
scientific analysis that helped to inform the treatment.
... Choosing the most suitable technique from the different available options depends on the size of the artwork, its value, the research interests and budget. The well-established traditional methodologies, such as ultraviolet-induced fluorescence (UVF), infrared reflectography (IRR), X-ray radiography (XRR) [4][5][6][7][8][9] are presently used together with more advanced techniques that enable the acquisition of multilevel information on pictorial materials, their distribution, and to some extent, also on their layering when suitable data-processing algorithms are used. These advanced imaging techniques include, multi-spectral imaging (MSI), hyper-spectral imaging (HSI), Macro X-Ray Fluorescence (Ma-XRF), and Time-Domain Terahertz imaging (THz-TDI), to name a few of the most significant [10][11][12][13][14][15][16][17][18][19][20][21]. ...
Imaging spectroscopy technique was introduced in the cultural heritage field in the 1990s, when a multi-spectral imaging system based on a Vidicon camera was used to identify and map pigments in paintings. Since then, with continuous improvements in imaging technology, the quality of spectroscopic information in the acquired imaging data has greatly increased. Moreover, with the progressive transition from multispectral to hyperspectral imaging techniques, numerous new applicative perspectives have become possible, ranging from non-invasive monitoring to high-quality documentation, such as mapping and characterization of polychrome and multi-material surfaces of cultural properties. This article provides a brief overview of recent developments in the rapidly evolving applications of hyperspectral imaging in this field. The fundamentals of the various strategies, that have been developed for applying this technique to different types of artworks are discussed, together with some examples of recent applications.
... Among imaging techniques [27] the most used are: RGB imaging that is commonly applied for documenting the surfaces under analysis [21,28]; raking light (RL) for the evaluation of detachments or surface defects [29]; UV fluorescence (UVf), which is commonly used for mapping of the organic materials such as lakes [30,31] or binders in secco paintings [21,32]; infrared reflectance (IR) [33,34] for unveiling the original drawing; Visible Induced Luminescence (VIL), a very powerful tool for mapping the presence of a specific pigment, the Egyptian Blue [35][36][37][38]. ...
The paper deals with the techniques and protocols used for studying wall paintings. A brief introduction about the more recent literature dealing with archaeometric and diagnostic analyses of wall paintings is reported. After that, the illustration of three case studies, spanning from Roman to contemporary wall painting are described.
... Many attempts have been made to avoid such errors but were finally replaced by cameras with a solid state array of PtSi (with a sensitivity of 1000-5000nm) initially, which required liquid nitrogen cooling Walmsley et al., 1993) until very recently InGaAs (sensitive to radiation between 900 and 1700 nm), which don't need a cooling system and is more efficient (Alexopoulou, 2018) . In order to achieve longer wavelengths, HgCdTe and InSb can be used, but these devices are considerably more expensive and need also cooling (Saunders et al. 2006). IRR at higher wavelengths presents an overall lower contrast and can also provide additional information as the absorption and reflection characteristic of many dyes is different in SWIR and MIR. ...
Paintings, mostly due to deteriorations, are sometimes repainted, concealing in underlayers important features, dates, names and other information. Conservators are facing dilemmas as to whether to preserve these interventions and retrieve valuable hidden information, but in the last decades the evolution of spectroscopic techniques has contributed to such uncertainties.
The current brief review explains the intentional repaint and presents the techniques used around the world to visualize the underpainting layers, and how these techniques have developed from a simple X-Ray radiography and an infrared (IR) photography to mobile devices with great imaging capabilities. Case studies include Byzantine icons and oil paintings.
... While various standards and certified targets exist for characterizing optical responses of imaging systems, these targets do not address the system's ability to detect hidden and fine details that are features of multi-material and multi-layered paintings. To this aim, custom built targets have been proven to be beneficial to test the usability of an imaging system for paintings investigations (Walmsley, Fletcher, and Delaney 1992;Delaney et al. 1993Delaney et al. , 2017Walmsley et al. 1994;Saunders et al. 2006). ...
Reflectance hyperspectral imaging provides a non-invasive tool for the diagnostics, analysis and documentation of paintings. It supplies high quality digital images with spectral information associated to each pixel of the imaged area. Working in the short-wave infrared range (1000–2500 nm) allows for the investigation of inner layers of paintings, by revealing underdrawings, hidden details, and characterizing artists’ materials. The performance of spectral imaging systems is usually established in the laboratory using reference targets to measure the system spatial and spectral resolution. However, when dealing with paintings, using custom built test targets made with materials more representative of the artwork can provide a better understanding of advantages and limitations of the system. This paper looks at the benefits of hyperspectral imaging in the 900–1700 nm region as applied to the study of paintings. A test panel target, made according to early Renaissance Florentine painting techniques was used for assessing the diagnostic capability of the hyperspectral system developed at the “Nello Carrara” Institute of Applied Physics. The paper illustrates how different spatial and spectral resolutions can impact the documentation of underdrawings and identification of artists’ materials. Finally, the analysis of a fifteenth-century panel painting by Fra Angelico is presented as case study.
... IR reflectography dates back to the '60s, and is based upon the fundamental work of Van Asperen de Boer [1,2], who laid the theoretical and experimental bases for this technique, and introduced the use of PbS Vidicon cameras. Traditionally performed by means of image detectors like CCD or Vidicon cameras [3][4][5][6][7], IR reflectography has evolved with the first scanning device in the '90s [8]. The main advantages of imaging sensors are their ease of use, portability and fastness. ...
InfraRed Reflectography (IRR) is traditionally used in the non-destructive diagnostics of ancient paintings to reveal features underlying the pictorial layer thanks to transparency characteristics to IR radiation of the materials composing the paints. Generally performed in wide-band modality, consisting in the acquisition of the radiation backscattered by a painting in a spectral range that depends on the detector used, it has recently been improved with the multispectral modality. Multi-spectral IR reflectography, based on reflectance measurement in narrow spectral bands, is presented herein. Main technologies, using either filters or dispersive systems, and the innovative scanner for multispectral IR reflectography are described. A few examples of application are shown, to highlight both the potential of multispectral analysis and its advantages over wide-band reflectography. The output is a stack of monochromatic images, one for each selected wavelength, which can be analysed separately as well as jointly. The multispectral option allows the choice of the most effective IR bands improving the ability to detect hidden features; interband comparison aids in localizing areas of different pictorial materials with particular IR reflectance. Besides the analysis of single monochromatic images, the joint processing of multispectral planes, such as subtraction and ratio methods, false colour representation and statistical tools, aids in enhancing details from hidden layers and providing information synthetized in a single image. Maintaining a visual approach in the data analysis allows this tool to be used by restorers and conservators, the actual end-users.
... Among imaging techniques [27] the most used are: RGB imaging that is commonly applied for documenting the surfaces under analysis [21,28]; raking light (RL) for the evaluation of detachments or surface defects [29]; UV fluorescence (UVf), which is commonly used for mapping of the organic materials such as lakes [30,31] or binders in secco paintings [21,32]; infrared reflectance (IR) [33,34] for unveiling the original drawing; Visible Induced Luminescence (VIL), a very powerful tool for mapping the presence of a specific pigment, the Egyptian Blue [35][36][37][38]. ...
The paper deals with the techniques and protocols used for studying wall paintings. A brief introduction about the more recent literature dealing with archaeometric and diagnostic analyses of wall paintings is reported. After that, the illustration of three case studies, spanning from Roman to contemporary wall painting are described.
... Infrared reflectograms were acquired with a commercial OSIRIS infrared camera, manufactured by Opus Instruments (Cambridge, United Kingdom). The OSIRIS was equipped with an InGaAs array sensor operating at wavelengths from 900 to 1700 nm, and object resolution down to 0.05 mm [13]. The painting was recorded with a camera-object distance of 133 cm, a focal length of 28 mm, an f/22 diaphragm and illuminated with two 300 W Halogen lamps. ...
The painting Saint Jerome, part of the collection of the Maagdenhuis Museum (Antwerp, Belgium), is attributed to the young Anthony van Dyck (1613–1621) with reservations. The painting displays remarkable compositional and iconographic similarities with two early Van Dyck works (1618–1620) now in Museum Boijmans van Beuningen (Rotterdam) and Nationalmuseum (Stockholm). Despite these similarities, previous art historical research did not result in a clear attribution to this master. In this study, the work’s authenticity as a young Van Dyck painting was assessed from a technical perspective by employing a twofold approach. First, technical information on Van Dyck’s materials and techniques, here identified as his fingerprint, were defined based on a literature review. Second, the materials and techniques of the questioned Saint Jerome painting were characterized by using complementary imaging techniques: infrared reflectography, X-ray radiography and macro X-ray fluorescence scanning. The insights from this non-invasive research were supplemented with analysis of a limited number of cross-sections by means of field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The results demonstrated that the questioned painting’s materials and techniques deviate from Van Dyck’s fingerprint, thus making the authorship of this master very unlikely.
... In principle, the imaging of static objects such as paintings may be acquired by means of scanning mechanisms, either in a plane parallel with and close to the painting [1] or in the focal plane of a large format camera [2][3][4]. ...
In this paper, we report on Vis-IR hyperspectral and terahertz imaging investigations carried out on a fresco painting on tavella depicting St. John Baptist, by Alessandro Gherardini (1655–1726). Measurements took place at the Restoration Laboratories of the former “Polo Museale della Toscana,” in Florence, in the framework of the Italy-Japan collaborative project THz-ARTE. We show how the hyperspectral data made it possible to determine the state-of-conservation of Gherardini’s painting, while reflection imaging measurements performed at 97 GHz provided a qualitative evaluation of the position of defects inside the tavella.
... Near-Infrared (NIR) reflectography is a well-established technique for painting diagnostics [1][2][3][4][5][6][7] , offering a fundamental contribution to the conservation of paintings [8][9][10][11][12] . Since the '80s it has been routinely applied to study the execution technique of the author, as well as the presence of pentimenti (an alteration in a painting, evidenced by traces of previous work, showing that the artist has changed his mind during the process of painting), retouches, integrations or underdrawing (the drawing realized on a painting ground before paint is applied). ...
Near-Infrared (NIR) reflectography is a well-established technique for painting diagnostics, offering a fundamental contribution to the conservation of paintings. Since the '80s it has been routinely applied to study the execution technique of the author, as well as the presence of pentimenti, retouches, integrations or underdrawing. In the last decades IR reflectography has been extended to the visible (VIS) spectral range, providing information about the pigment composition. Up to now the multispectral analysis is still applied at an experimental level, as the processing of the image set is not straightforward.
Rarely multispectral VIS-IR application has been applied to frescos, probably due to the lack, in most cases, of a scattering background.
In this work we present the results provided by a multispectral scanning device based on single sensor acquisition, working in the 380-2500 nm spectral range, that is a laboratory prototype specifically built for research-grade imaging. The technique have been applied on a mock up simulating a mural painting substrate where an underdrawing, made of either carbon or iron-gall ink, was covered by different surface layers of limewash, the so-called scialbo.
... Truly portable sensors place the raster-scanning detector elements(s) in the focal plane of a lens having a large field of view (FOV). Such systems provide 16-megapixel images (4k-by-4k) by scanning, using either a small-area array [10] or a line array [11]. Those systems have limitations given their low collection efficiency (area covered per unit time), which diminish their utility when used with spectral band filters. ...
The registration of technical art conservation images of Old Master paintings presents unique challenges. Specifically, X-radiographs and reflective infrared (1000–2500 nm) images reveal shifted, or new, compositional elements not visible on the surface of artworks. Here, we describe a new multimodal registration and mosaicking algorithm that is capable of providing accurate alignment of a variety of types of images, such as the registration of multispectral reflective infrared images, X-radiographs, hyperspectral image cubes, and X-ray fluorescence image cubes to reference color images taken at high spatial sampling (300–500 pixels per inch), even when content differences are present, and a validation study has been performed to quantify the algorithm’s accuracy. Key to the algorithm’s success is the use of subsets of wavelet images to select control points and a novel method for filtering candidate control-point pairs. The algorithm has been used to register more than 100 paintings at the National Gallery of Art, D.C. and The Art Institute of Chicago. Many of the resulting registered datasets have been published in online catalogues, providing scholars additional information to further their understanding of the paintings and the working methods of the artists who painted them.
... This lucky circumstance is why the text becomes visible against a clear background in infrared images. Infrared reflectography (IRR) in the near infrared [1][2][3], is therefore the papyrologist's tool of choice for the examination and documentation of these objects [4][5][6][7][8][9]. ...
Imaging techniques are commonly used to improve the legibility of text in ancient or degraded documents. Infrared reflectography is one of the best methods for examining documents written in a carbon-based ink since the contrast between the ink and the support is usually much greater in that band. In these cases, for archival and study purposes, the visible and the corresponding infrared images are usually shown next to one another. In other cases, like e.g. papyri, this separation between text and background is not easily achievable, and therefore, a more sophisticated elaboration is needed. Moreover, in these cases, the background is a relevant source of information on the original document, and thus its integration with the extracted text could represent an effective solution for scholars. In this paper, we present a new method to improve the legibility of the text in visible light reflectance images without altering the appearance of the support. The method is based on the fusion of the text extracted from the infrared image with the visible image. The contrast of the text in the infrared image is first enhanced with the Automatic Color Equalization algorithm, a perceptual-based enhancement technique, and then extracted with a thresholding process. The proposed method allows to visualize different information (text, background, alterations, etc.) on a single image, and can be also used for an efficient archival approach.
... Truly portable sensors place the raster-scanning detector elements(s) in the focal plane of a lens having a large field of view (FOV). Such systems provide 16-megapixel images (4k-by-4k) by scanning, using either a small-area array [10] or a line array [11]. Those systems have limitations given their low collection efficiency (area covered per unit time), which diminish their utility when used with spectral band filters. ...
As high-resolution conservation images, acquired using various imaging
modalities, become more widely available, it is increasingly important
to achieve accurate registration between the images. Accurate
registration allows information unavailable in any one image to be
compiled from several images and then used to provide a better
understanding of how a painting was constructed. We have developed an
algorithm that solves several important conservation problems: 1)
registration and mosaicking of multiple X-ray films, ultraviolet images,
and infrared reflectograms to a color reference image at high
spatial-resolution (200 to 500 dpi) of paintings (both panel and canvas)
and of works on paper, 2) registration of the images within visible and
infrared multispectral reflectance and luminescence image cubes, and 3)
mosaicking of hyperspectral image cubes (400 to 2500 nm). The
registration/mosaicking algorithm corrects for several kinds of
distortion, small rotation and scale errors, and keystone effects
between the images. Thus images acquired with different cameras,
illumination, and geometries can be registered/mosaicked. This automatic
algorithm for registering/mosaicking multimodal conservation images is
expected to be a valuable tool for conservators attempting to answer
questions regarding the creation and preservation history of paintings.
For example, an analysis of the reflectance spectra obtained from the
sub-pixel registered multispectral image cubes can be used to separate,
map, and identify artist materials in situ. And, by comparing the
corresponding images in the X-ray, visible, and infrared regions,
conservators can obtain a deeper understanding of compositional changes.
... This picture usually provides a 2D map in which features that are not detectable through visual examination can be pointed out. The use of imaging techniques in the art conservation field ranges from well-established methodologies, such as high-resolution digital photography, visible raking light, UV fluorescence, XRR, IR reflectography, etc., to cuttingedge applications, such as multi-and hyper-spectral imaging techniques [19,20] or THz imaging [21]. In principle, all the above techniques could be used in order to reach the desired level of knowledge on the object under analysis. ...
Terahertz (THz) imaging is an emerging technique for the non-invasive
analysis of artworks. Since THz waves can penetrate opaque materials,
various imaging systems that make use of THz waves have been developed
in order to detect certain chemicals and defects in materials. More
recently, THz imaging has been applied to the examination of works of
art. The first experiments in the use of THz imaging in the field of art
have provided very encouraging results.
... OCT has been found to be particularly effective at high-resolution and high-contrast imaging of underdrawings owing to the advantages of interferometry [5,10]. Figure 10 shows an example where OCT has given images of underdrawing at a higher resolution and greater contrast than those obtained with an InGaAs near-infrared camera [25]. Figure 11 gives an example of a painting where the OCT image at 930 nm shows limited ability to reveal an underdrawing line where the near-infrared image (InGaAs detector 900-1,700 nm) shows it clearly. ...
Optical coherence tomography (OCT) has been shown to have potential for important applications in the field of art conservation and archaeology due to its ability to image subsurface microstructures non-invasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artists’ paints. VIS–NIR (400–2,400 nm) reflectance spectra of a wide variety of paints made with historic artists’ pigments have been measured. The best spectral window with which to use OCT for the imaging of subsurface structure of paintings was found to be around 2.2 μm. The same spectral window would also be most suitable for direct infrared imaging of preparatory sketches under the paint layers. The reflectance spectra from a large sample of chemically verified pigments provide information on the spectral transparency of historic artists’ pigments/paints as well as a reference set of spectra for pigment identification. The results of the paper suggest that broadband sources at ~2 μm are highly desirable for OCT applications in art and potentially material science in general.
... Image acquisition was carried out with the standard Osiris infrared camera [8], developed by the National Gallery and currently used in many museums. The device is based on an InGaAs array sensor with sensitivity in the 900-1700 nm range and sampling grid up to 4096x4096 pixels, which allows image capture with a spatial resolution down to 50 µm (with standard optics). ...
Near infrared imaging is a powerful technique for the analysis of ancient paintings, allowing the nondestructive examination of features underneath the pictorial surface. Beyond the unique nature of the artwork (materials and layer stratigraphy), the effectiveness of the technique in detecting any painting features is determined by the device performance (spectral sensitivity, acquisition band narrowness, spatial resolution) as well as by the irradiation setup. We performed multi-modal infrared imaging on a XVI century masterpiece by Titian using an InGaAs camera and different measurement setup. Acquisition was carried out in conventional reflection geometry and in trans-irradiation mode, as well as in wideband and multispectral modes. Preliminary results are presented and the potentialities of such infrared analysis discussed.
... In the past years, several types of scanners have been proposed although for the purpose of this article, we will only briefly remind the working principles of the Image Plane Scanner (IPS) [9,10] and of the Moving Lens Scanner (MLS) [11]. ...
Infrared reflectography is an imaging technique used to visualize the underdrawing of ancient paintings.
An underdrawing is a preparatory drawing sketched by the artist on the preparation layer before the
painting is made. Pigment layers are quite transparent to infrared radiation in the spectral band between
0.8 and 2.5 microns. The preparation layer normally reflects the infrared radiation except where it is
adsorbed by the underdrawing made with a carbon‐base material. Infrared sensitive devices can therefore
record the reflected radiation and store an image of the underdrawings. InGaAs sensor cameras are
nowadays the most used devices to visualize the underdrawing. Due to the small size of InGaAs detectors,
these are usually mounted on image plane scanning systems to record high resolution reflectograms. This
article describes a portable scanning system based on a motorized panoramic‐head which can be built at a
lower cost than commercial reflectographic systems. The system performance is comparable with that of
other reflectographic devices with the advantage to extend the scanned area up to 1x1 m.
... Infrared photography was limited to the real near-infrared, a range approximately between 700 nm and 900 nm. Modern infrared reflectography (IRR), a commonly used and non-destructive technique for the investigation of ancient paintings, makes use of digital cameras, whose incorporated CCD sensors are inherently sensitive to infrared light, in that way images with a wavelength from 800 nm to 2000 nm may be obtained [2]. The instrumental setup of an investigation employing IRR is depicted infigure 1. ...
A 3D laser scanning instrument, equipped with an optical transmitter containing a continuous 785 nm
diode laser, was used in order to obtain infrared reflectography data of oil paintings. The investigation
was carried out in two modern oil and acrylic paintings on canvas and a late 16th century panel painting.
In the first case results were compared with existing documentation of the artistic process and in the
second with a previously elaborated study by IR reflectography. Data recording took as short as five
minutes, providing an IR image comparable to those obtained by reflectography in the IR-A zone of the
spectrum. The technique additionally provides high resolution topographic data of the artworks’ surrounding,
such as frame and adjacent walls, and has potential to be developed into an alternative
method for investigation of pigment layers on virtually any surface, especially if these are of great
dimensions or almost inaccessible.
... Infrared reflectograms of 14 single folios and three openings of the Liber Floridus were made with an OSIRIS infrared camera, operating at wavelengths from 900 to 1700 nm. The prototype of this camera was developed at the scientific department of the National Gallery London, and taken into production by Opus Instruments Ltd. [29]. The OSIRIS camera has an InGaAs array sensor with an object resolution down to 0.05 mm. ...
Розглянута еволюція дослідження творів мистецтва в інфрачервоному випромінюванні, проаналізована від фотофіксації на сенсибілізовані фотоплівки до сучасного методу мультиспектральної візуалізації. Виявлені передумови появи, особливості розвитку та можливості методів інфрачервоної фотографії та рефлектографії, інфрачервоної люмінесценції та методу хибнокольорових зображень в інфрачервоному діапазоні.
The 555 drawings by Leonardo at Windsor Castle, almost all from his studio at his death, permit a comprehensive survey of his drawing materials. In recent years, a wide range of techniques have been employed to study these materials, and the results of these investigations are presented here. These include transmitted light, to study paper structure and watermarks; stereo microscopy; raking light with digital subtraction of images, to reveal his use of blind stylus; infrared reflectance imaging, to study carbon-based underdrawing and to distinguish silverpoint from leadpoint; ultraviolet imaging, to recover faded metalpoint drawings; X-ray fluorescence, to produce element maps and suggest the reasons for this fading; and Raman spectroscopy, to determine the chemical compounds in some of Leonardo’s pigments and dyes.
This paper presents the first art-technological approach on Georg Flegel's (1566-1638) painting technique, a 17th century Frankfurt based artist and one of the originators in the
development of still life paintings as an autonomous genre. Five chosen paintings were examined by non-destructive in-situ analysis techniques at the Stadel Museum in Frankfurt. In detail, infrared reflectography (IRR), X-ray radiography (XRR), macro X-ray fluorescence analysis (MA-XRF) and microscopic investigations were used. Although comprehensive research on Flegel's oeuvre involving technical examination is still lacking, derivations on the lifelong development of Flegel's painting technique as well as information on the workshop practice of the artist could be gained from the outcomes of this research.
Au cours de cette recherche, nous avons contribué à l’étude et à la caractérisation des pigments utilisés par le peintre français Étienne Dinet à l’aube du XXe siècle. Notre approche a consisté à nous appuyer sur les manuels de peinture écrits par le peintre (Les fléaux de la peinture) dans lesquels il expose sa recherche des matériaux à utiliser en peinture. En nous basant sur ces écrits, nous avons créé une base de données de photographies scientifiques et de spectres de réflectance (visible et proche infrarouge) pour pouvoir déterminer les pigments employés dans ses tableaux. Sept tableaux ont ensuite étudié. L’imagerie scientifique nous a permis de caractériser la palette du peintre, en particulier lorsque nous avons eu la possibilité d’associer plusieurs techniques d’analyse produisant des données complémentaires. Nous avons ainsi montré l’intérêt d’employer simultanément un ensemble de techniques non invasives d’imagerie pour la caractérisation des pigments : aucun prélèvement de matière picturale n’est nécessaire et la faible quantité de lumière irradiant l’œuvre durant les mesures n’affecte pas sa conservation. La photographie technique peut fournir de nombreuses informations sur l’état de conservation d’une peinture et nous permet de détecter les interventions de restaurations effectuées au cours du temps. Elle nous permet aussi de formuler des hypothèses sur la palette du peintre. Pour confirmer ces hypothèses, il est nécessaire d’effectuer des analyses comme la fluorescence des rayons X et l’imagerie hyperspectrale, qui fournissent des informations plus précises et dont l’interprétation est plus certaine.
This book details the application of advanced characterisation techniques and diagnostic tools to heritage science, including the evaluation of heritage assets’ condition, their preservation and restoration.
It examines the use of electrochemical techniques in conservation science, with a particular focus on how to solve problems in taking on-site measurements. Specifically, it introduces readers to a new gel polymer (GPE) electrochemical cell developed by the authors for the characterisation of metallic heritage objects. Other techniques used to characterise and monitor reinforced concrete objects in more modern buildings are also covered, including non-destructive electrochemical techniques that allow steel corrosion to be assessed in these structures, and in those that are used to protect and repair such buildings.
The usefulness of the NMR-Mouse nuclear magnetic resonance sensor in the assessment and preservation of softer heritage materials, such as wood, parchment, bone, and painted walls, is covered, as well as Infrared reflectography for examining paintings and laser cleaning for restoring them. The book introduces ultra-High Performance Liquid Chromatography (u-HPLC) with a diode-array (DAD) and mass–mass (MS-MS) quadruple time-of-flight spectroscopy (QTOF). This new technique can be applied to the analysis and identification of natural and synthetic organic pigments and its use is demonstrated in several case studies.
This book provides a rigorous scientific grounding in the application of state-of-the-art techniques in heritage science and conservation, and offers a practical handbook for practitioners.
To date, more than 800 paintings at the Art Gallery of Western Australia have been surveyed using an indium gallium arsenide (InGaAs) infra-red reflectography system, revealing varied information about artist materials and their state of preservation: hidden inscriptions, skulls, nudes and other reworkings come to light using a portable system which rapidly captures images across exhibition walls and storage racks. This survey attempts to group information according to artist, period and materials and shows that underdrawing is not limited to more traditional oil paintings but also occurs in contemporary art where prudery and cost of materials are less of an issue.
The construction and examination of test panels is an ad hoc procedure, necessary for every spectral imaging study of paintings. Despite the common features, almost every scientific team follows a different way of construction. Furthermore, many of these approaches are not adequately documented in the relevant papers. Failure to use common language and practice leads to confusion about properties of materials and paint layers that have been overall examined by the scientists, as well as the validity of the results and their exploitation in several conservation applications. The present theoretical approach points out the need for common protocols for the construction of test panels and draws general principles as a flow chart on which they should be based.
Information on the creation of a painting lies usually hidden under the surface. A painting's substructure may include the underdrawing, underpainting, modifications to the initial setup (or pentimenti), and sometimes even abandoned compositions. Traditionally, the study of these characteristics relies on penetrative, two-dimensional imaging techniques (infrared reflectography, x-ray radiography) complemented with selected paint crosssections. The limitations of this approach are twofold. First, it can be difficult to combine data from cross sections with two-dimensional images, because of poor redundancy of both methods. Second, cross sections involve destructive sampling of the paint layer. This paper introduces synchrotron radiation computed micro-laminography in the study of paintings. The technique allows for three-dimensional imaging of the paint stratigraphy in a nondestructive manner, enabling the imaging of paint layers, their interfaces, the ground, and carrier. The technique is demonstrated on a test painting, and its interest to curators and conservators of painting collections is discussed.
In the study of cultural heritage, most of the analytical techniques are point-specific or give information about small areas of the object. Therefore it is essential to obtain an overview of which points are suitable for these further investigations. To fulfill this, a first imaging study is the best way to proceed. Hereby, we can record the entire piece at once and observe the behavior and relation between different materials of the object. Various types of light can be used to obtain a selection of images and consequently also different information about the artifacts. Among them, infrared (IR) photography can be used as a first analysis, for instance, to reveal the pigments’ response upon interaction with IR radiation.
In following we will present results obtained via IR video-photography on a selection of painted objects from the Mexican cultural heritage. These items are analyzed by False Color procedure, where colors are assigned to every grey tone of the pure IR photo. Hereby it is possible to distinguish between certain pigments on the painted surface.
In this paper we demonstrate that by means of scanning reflection FTIR spectroscopy, it is possible to record highly specific distribution maps of organic and inorganic compounds from flat, macroscopic objects with cultural heritage value in a non-invasive manner. Our previous work involved the recording of macroscopic distributions of chemical elements or crystal phases from painted works of art based on respectively macroscopic X-ray fluorescence or X-ray powder diffraction analysis. The use of infrared radiation instead of X-rays has the advantage that more specific information about the nature and distribution of the chemical compounds present can be gathered. This higher imaging specificity represents a clear advantage for the characterization of painting and artist materials. It allows the distribution of metallo-organic compounds to be visualized and permits distinguishing between pigmented materials containing the same key metal. The prototype instrument allows the recording of hyperspectral datacubes by scanning the surface of the artefact in a contactless and sequential single-point measuring mode, while recording the spectrum of reflected infrared radiation. After the acquisition, spectral line intensities of individual bands and chemical distribution maps can be extracted from the datacube to identify the compounds present and/or to highlight their spatial distribution. Not only is information gained on the surface of the investigated artefacts, but also images of overpainted paint layers and, if present, the underdrawing may be revealed in this manner. A current major limitation is the long scanning times required to record these maps.
En face optical coherence tomography (OCT) delivers slices in the tissue
with an orientation similar to that of confocal microscopy and of
thickness determined by the coherence length of the broadband excitation
source. En face OCT has progressed along two main avenues, full-field
and flying spot. In the flying spot implementation, the path modulation
introduced by the transverse scanners may be employed to generate en
face OCT images. En face OCT is a time domain method. In an era
dominated by spectral domain methods, en face OCT has unique features
not achievable via spectral domain methods, such as versatile operation
in A, B, C scanning regimes, compatibility with simultaneous confocal
imaging, dynamic focus, simultaneous imaging at several depths and
measurement of topography, and orientation of surfaces in a single frame
During the past two decades, thanks to the rapid development of solid-state-based sensor technology, digital imaging emerged as one of the most attractive research areas for the noninvasive investigation of paintings and flat artworks. In particular, the commercial availability of high-performance digital cameras opened up new perspectives to transmitted imaging techniques, such as trans-illumination and trans-irradiation, which are based on the acquisition of the visible (Vis) and near infrared (NIR) radiation, respectively, transmitted through the object. Until recently, these techniques were indeed considered to be unsuitable for applications on artefacts, because of the risks of overheating and overexposure to the light of the object under analysis. Nowadays, with the new-generation digital cameras, transmitted imaging can be reconsidered as a possible tool for noninvasive diagnostics on paintings on canvas. These techniques have been proven to be effective for the examination of hidden details, such as underlying drawing, for a study of the pictorial style or the executive techniques, as well as for assessing the state of conservation of the supports. Both trans-illumination and trans-irradiation can be easily implemented by means of professional photographic digital cameras, and therefore offer a valuable alternative to the more expensive well-established methodologies, such as X-ray radiography. In some cases, they are found to be complementary to the conventional techniques in revealing details of the underlying paint layers. Potentials and limits of transmitted imaging techniques are discussed in this paper, starting from three case studies of oil-paintings on canvas that belong to the permanent collection of the Gallery of modern art at the Pitti Palace in Florence.
Hidden, sub-surface paint layers and features contain valuable information for the art-historical investigation of a painting's past and for its conservation for coming generations. The number of techniques available for the study of these features has been considerably extended in the last decades and established techniques have been refined.
This review focuses on mobile non-destructive subsurface imaging and depth profiling techniques, which allow for the in-situ investigation of easel paintings, i.e. paintings on a portable support.
Among the techniques discussed are: X-ray radiography and infrared reflectography, which are long established methods and are in use for several decades. Their capabilities of element/species specific imaging have been extended by the introduction of energy/wavelength resolved measurements.
Scanning macro-X-ray fluorescence analysis made it for the first time possible to acquire elemental distribution images in-situ and optical coherence tomography allows for the non-destructive study the surface paint layers in virtual cross-sections.
These techniques and their variants are presented next to other techniques, such as Terahertz imaging, Nuclear Magnetic Resonance depth profiling and established techniques for non destructive testing (thermography, ultrasonic imaging and laser based interference methods) applied in the conservation of historical paintings.
Next to selected case studies the capabilities and limitations of the techniques are discussed.
Thermal Quasi Reflectography (TQR), e.g. imaging in the thermal band 3-5 μm (MWIR), is discussed as innovative tool for the noninvasive analysis of pictorial surface layers in artworks, and its potential is demonstrated in some applications. The results encourage further developments in this field. The novel experimental technique, which has been recently introduced by the authors, is reviewed here giving focus to current research and potential applications.
We present a proto-type portable remote multispectral imaging system, PRISMS (Portable Remote Imaging System for Multispectral Scanning), that is light-weight, flexible and without any cumbersome mechanical structure for in situ high resolution colour and spectral imaging of large and inaccessible paintings such as wall paintings. This is the first instrument to be able to image paintings at inaccessible heights in situ from ground level to produce not only high resolution colour images but also multispectral images.
Voltammetry of microparticles, an electrochemical methodology based on the record of the voltammetric response of sparingly soluble solids mechanically transferred to the surface of inert electrodes in contact with suitable electrolytes, is able to provide significant analytical information in the fields of conservation and restoration of cultural goods. Using this methodology, identification, speciation, and relative and absolute quantification of analytes from works of art samples can be achieved. Applications to the analysis of organic and inorganic pigments in paints, fibbers, ceramic materials as well as alteration compounds in paintings and metallic artifacts are reviewed.
The assembly of infrared reflectogram mosaics is, despite many improvements, a lengthy process highly dependent on the skill of the individual conservator. The National Gallery, London, has developed an image-processing system which, when used in conjunction with conventional infrared reflec- tography equipment, greatly expedites the assembly of mosaics and overcomes the problems associated with accurately aligning adjacent images. The equipment used, the procedure for acquiring images and a new technique for joining images are described. A com-parative example illustrates both the improved quality of the final reflectograms and the reduced time required for their completion.
Infra-red reflectography, a method of improving the detect ability of underdrawings in medieval paintings, is discussed. It is shown that the results can be explained with the Kubelka-Munk analysis of the optical properties of paint films. Measurements are described providing a plot of the paint layer thickness required to hide an underdrawing, against the wavelength. Such curves show a maximum around λ = 2.0 microns. Infra-red to visible image translation systems are surveyed to illustrate the choice of an infra-red vidicon television system to obtain reflectograms. This system is responsive to radiation up to 1.9 microns. The interpretation of infra-red reflectograms is briefly discussed. Limitations of the method are indicated.
The assembly of infrared reflectogram mosaics is, despite many improvements, a lengthy process highly dependent on the skill of the individual conservator. The National Gallery, London, has developed an image-processing system which, when used in conjunction with conventional infrared reflectography equipment, greatly expedites the assembly of mosaics and overcomes the problems associated with accurately aligning adjacent images. The equipment used, the procedure for acquiring images and a new technique for joining images are described. A comparative example illustrates both the improved quality of the final reflectograms and the reduced time required for their completion. /// Le montage de mosaïques d'images de réflectogrammes infrarouge reste, malgré de nombreuses améliorations, un processus lent, dépendant énormément de l'adresse personnelle du practicien. La National Gallery de Londres a mis au point un système de traitement d'image qui, utilisé conjointement avec un équipement de réflectographie conventionnel, accélère considérablement le montage des mosaïques et élimine les problèmes relatifs à la précision du calage d'images adjacentes. On décrit l'équipement utilisé, la procédure de saisie des images et une nouvelle technique pour assembler celles-ci. Un exemple comparatif permet d'illustrer aussi bien l'amélioration de la qualité du réflectogramme final que la réduction du temps nécessaire à son obtention. /// Trotz aller Verbesserungen ist die Montage von Infrarotreflektographien ein langwierlger Prozess, dessen Ergebnis in hohem Maße vom Geschick dessen abhängt, der die Montage fertigt. Die Londoner National Gallery hat ein Bildverarbeitungssystem entwickelt, das in Verbindung mit einer konventionellen Anlage zur Infrarotreflektographie die Montage deutlich beschleunigt. Insbesondere wurden Probleme mit den Nahtstellen benachbarter Bilder gelöst. Der Beitrag beschreibt die Apparatur, den Prozess der Bildaufnahme und ein neues Verfahren zum 'Vernähen' der (digitalisierten) Bilder. In Gegenüberstellung mit einer photographischen, konventionellen Infrarotmontage werden die verbesserte Qualität der neuartigen Infrarotmontage und der damit verbendene Zeltgewinn aufgezeigt.
A method is described for the evaluation of the performance of near-infrared imaging devices to detect underdrawing and reworking of paintings. System analyses have been performed on two different near-infrared imaging devices: a Hamamatsu lead sulphide vidicon camera and a Photometries silicon charge coupled device (CCD) camera. The analyses included modelling of the system spectral response curve by analysis of the system components, as well as considering the limiting resolution and modulation transfer function (MTF). The modelling was confirmed by examination of a test panel at various wavelengths. Calculation of visibility is introduced as a quantitative measure of system performance. This calculation is also discussed as a means to define more clearly the actual performance requirements of these systems. This analysis has revealed the strengths and weaknesses of current systems, and provides guidance in the construction of improved devices.
In recent years digital imaging has proved to be a useful tool for documenting and examining paintings. These techniques can yield permanent records that are potentially more accurate than photographic images. The key applications in which digital imaging is superior to other techniques are those where short- or long-term changes are measured. The paper describes the imaging systems developed in a ten-year collaboration between the National Gallery, London and the Doemer- Institut, Munich and the geometric transformation algorithms which have allowed accurate comparisons of ‘before’ and ‘after’ images to be made. Recent results obtained from a long-term study of colour changes caused by display in the museum and short-term changes caused by transportation to loan exhibitions are presented. Improvements made to the procedure for acquiring, processing and presenting infrared reflectogram mosaics are also detailed. Finally, other conservationrelated and archival uses for the colour-accurate, high-resolution digital images are discussed.
Infrared imaging technologies have traditionally been used to investigate and elucidate images underlying Old Master paintings. Application to works from the twentieth century has proved to be exceptionally fruitful as well. The varied materials of twentieth-century art require adaptation of the infrared imaging set-up to utilize the equipment fully. These variations of set-up, cameras, lights, image digitization and image processing are discussed. Infrared examinations of works by Ernst, Miro, Warhol, Johns and Pollock are presented. Issues of interpretation of these studies, particularly in the case of abstract images, are also explored.
This contribution attempts a better understanding and, where possible, an optimization of the components in the ‘image chain’ of infrared reflectography. It aims to protect the object against radiation in excess of that required for image acquisition, to reveal more of the underdrawing than does the conventional procedure, and to increase the image quality of both the single reflectograms and the assembled mosaic. The automatic acquisition uses a positioning system in which the camera is moved while the object remains stationary. ProcessIng and automatic mosaicing of the digitized reflectograms are done on a computer workstation. The results are demonstrated on a late eighteenth-century painting by J. G. von Dillis.
The SWIR subband presents a growing interest for military, commercial and space applications such as non-destructive test, spectrometry, hyperspectral instruments. In addition to the interest of this specific waveband, these detectors present the advantage of a combination of high performance with the use of thermoelectrical cooler for cooled and uncooled applications. Thus, in order to answer the different market needs for these types of applications, Sofradir has developed different IR detectors in the SWIR waveband. Sofradir offers a 2.5μm cut-off operating around 200K, a 2μm cut-off operating at 250K and a 1.6μm cut-off operating at ambient temperature. The main characteristics and performance results are given as well as the main trade-offs achieved for large quantity productions.
The Methodology for Art Reproduction in Colour (MARC) project has included the development of a large-format digital camera capable of making images of up to 20,000 x 20,000 pixels, albeit slowly. Later developments are summarised. The MARC II camera uses micro- and macropositioning to give a color image of approximately 10,000 x 10,000 pixels with improved data transfer and mechanical positioning. The calibration and operation of such a camera for both large and small paintings and the workflow for recording, processing, and storing high-resolution images are described.
Describes the second-generation system used to detect and measure changes in the surface colour of paintings. It comprises a high-resolution monochrome digital camera mounted on a positioning system, which carries a filter set placed in front of the camera. Areas of the painting and of calibration charts are illuminated sequentially through the filters, and combined into a high-resolution colourimetric image of the whole painting. At times 10-20, or even 40 pixels (picture elements) per mm are required to give adequate resolution, and large paintings are dealt with by taking subimages and combining them electronically. Details of the equipment, calibrations, storage of data, etc. are given. Changes in surface texture after transport can also be measured.
Infrared Detectors and Systems
- E L Dereniak
- G D Boreman
A scanning device for infrared reflectography
- D Bertani
- M Cetica
- P Poggi
- G Puccioni
- E Buzzegoli
- D Kunzelman
- S Cecchi
Beneath the surface of old pictures
- F I G Rawlins
A microscan/ macroscan 3 x 12 bit digital color CCD camera with programmable resolution up to 20
- R Lenz
- R Beutelhauser
- U Lenz
Evaluation of platinum silicide cameras for use in infrared reflectography
- E Walmsley
- C Metzger
- C Fletcher
IR-colour scanning reflectography', in The Painting Technique of Pieretro Vannucci. called il Perugino
- L Pezzati
- M Materazzi
- P Poggi
Assembly of infra-red reflectograms by digital processing using a portable data collecting system
- G Wecksung
- R Evans
- J Walker
- M Ainsworth
- J Brealey
- G Carriveau
La riflettografia infrarossa
- D Bertani