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36 The principle of first and second curtain of a focal plane shutter. (1-5) depict the individual steps of a slow shutter speed, while (6) represents a fast shutter speed.
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All Virtual reality, augmented reality, mixed reality or straight-up video games can now be found in growing numbers within spaces dedicated to culture and the arts. The choice of such tools is trans-forming the traditional museum tour into a multifaceted and interactive experience to the point, in some cases, of flirting with entertainment. From o...
In recent years, we have assisted to an impressive advance of computer vision algorithms, based on image processing and artificial intelligence. Among the many applications of computer vision, in this paper we investigate on the potential impact for enhancing the cultural and physical accessibility of cultural heritage sites. By using a common smar...
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... To achieve a Depth of Field (DoF) that allowed focusing on the turntable 30 cm in diameter, the camera, a Nikon D750 with a Nikon AF 28-105 f/3.5-4.5 lens, was positioned at ≈70 cm with a focal length of 38 mm and an aperture of f/18, leading to an increased exposure time (Nicolae et al., 2014;Verhoeven, 2016). Six orbits around the object were performed, taking shots with the camera tilted at approximately 45 • and 20 • , and two sets with frontal shots, ensuring that each point was well visible in a large number of photos (Menna et al., 2017;Collins et al., 2019). ...
... To answer the art historical questions, it was requested that features in the order of 1 mm could be detected in both the 3D model and orthophoto imagery. Therefore, a Ground Sampling Distance (GSD) of at most .5 mm and ideally .25 mm would be required (Verhoeven, 2016). ...
3D imaging of large painted and vaulted historic ceilings offers many challenges, including those due to complex small and large-scale geometry, environmental conditions and limited access. In this paper we introduce CHAPI (Cultural Heritage Automated Photogrammetric Imaging), a low cost solution to these problems which provides an efficient, semi-automated method of capturing large vaulted ceiling paintings in high detail, with a consistent photogrammetric network and in limited time. We will present and examine two different case studies from the Plafond3D project, the baroque ceiling paintings of the Schloss Rheinsberg Spiegelsaal (mirror room) and the Ansbach Residence Festsaal (great hall/ballroom). The paper will examine the particular challenges of capturing large painted areas with accurate colour and geometric reproduction, and suggest how the photogrammetric recording and reconstruction process of ceilings can be optimised for large rooms. This paper also gives technical specifications and Open Access Code for the CHAPI build.
... There can be two types of device architecture for panchromatic imaging. Figure 1A compares the typical parallel (24) and stacking (25) design. The parallel architecture has been ubiquitously applied in the commercial digital camera, with the incident white light being spatially dispersed into R/G/B through a complimentary CFA followed by detection of a color-blind sensor array. ...
The retina is the essential part of the human visual system that receives light, converts it to neural signal, and transmits to brain for visual recognition. The red, green, and blue (R/G/B) cone retina cells are natural narrowband photodetectors (PDs) sensitive to R/G/B lights. Connecting with these cone cells, a multilayer neuro-network in the retina provides neuromorphic preprocessing before transmitting to brain. Inspired by this sophistication, we develop the narrowband (NB) imaging sensor combining R/G/B perovskite NB sensor array (mimicking the R/G/B photoreceptors) with a neuromorphic algorithm (mimicking the intermediate neural network) for high-fidelity panchromatic imaging. Compared to commercial sensors, we use perovskite "intrinsic" NB PD to exempt the complex optical filter array. In addition, we use an asymmetric device configuration to collect photocurrent without external bias, enabling a power-free photodetection feature. These results display a promising design for efficient and intelligent panchromatic imaging.
... Working with uncompressed TIFFs is very important for image analysis, especially for processing the principal component analysis (PCA) and the image calculations for the different false colour and hybrid images. Using lossy compression images such as JPGs may cause artefacts [44], compromising the final results and thus possibly causing misinterpretation. ...
A workflow for the photogrammetric combination of non-invasive multispectral imaging techniques ranging from ultraviolet (UV) and visible (VIS) to near infrared (NIR) for the investigation of wall paintings is presented. Hereby, different methods for image analysis and visualisation techniques are discussed. This includes the combination of spectral bands in hybrid false-colour images and image analysis by applying NDVI/NDPI and PCA. The aim of the research is to generate a high-resolution photogrammetric image set, providing information on underdrawings, material differences, damages, painting techniques and conservation measures. The image data are superimposed with pixel accuracy in a geographic information system (GIS) for further analysis, tracing of observations and findings and the annotation of further information. The research is carried out on the ‘Adoration of the Shepherds’, an early Spanish Renaissance wall painting created in 1472 by Paolo de San Leocadio and Francesco Pagano in the Cathedral of Valencia. The wall painting is preserved in an unfinished condition, and half of it is represented by the initial plaster and preparation layers. This gives the possibility to compare and evaluate the observations of the finished areas as well as carry out an in-depth study of the working techniques.
... Precise digitization facilitates the preservation of a real object's color and appearance in optimal circumstances and provides a digital simulation available for research at large (Li et al., 2000(Li et al., , 2013Granzier et al., 2009;Akazawa et al., 2021). In the early years, conservators and conservation scientists preserved murals by taking pictures using filmbased photography because good digital cameras did not have sufficient image quality (Verhoeven, 2016). After that, highresolution scanning and processing of the negative analog film frames needed to be performed to achieve digitization and saved as tiff image format. ...
... (c) The lens vignetting or light falloff with spherical aberration could result in an image that is brighter in the middle and darker around the edges because the stronger the refracted light, the more significantly the imaging signal will be reduced; this effect is especially prominent for wide-angle lenses. In most cases, the illumination is brightest in the middle of the image, with a steady decrease toward the edges (Verhoeven, 2016). (d) Most color constancy algorithms assume that the incident illumination remains constant across a scene, but this assumption is very often not valid for real images (Cardei et al., 2002). ...
Restoring the correct or realistic color of a cultural heritage object is a crucial problem for imaging techniques. Digital images often have undesired color casts due to adverse effects caused by unstable illuminant conditions, vignetting, and color changes due to camera settings. In this work, we present an improved color correction method for color cast images that makes the color appear more realistic. It is based on a computational model of the human visual system that perceives objects by color constancy theory; it realizes illumination non-uniformity compensation and chromaticity correction for color cast images by taking into account the color stability of some pigments. This approach has been used to correct the color in Cave 465 of the Mogao Grottoes. The experimental results demonstrate that the proposed method is able to “adaptively correct” color cast images with widely varying lighting conditions and improve the consistency efficaciously. It can achieve improved consistency in the mean CIEDE2000 color difference compared with the images before correction. This colorimetric correction methodology is sufficiently accurate in color correction implementation for cast images of murals captured in the early years.
... However, reliable change detection, smooth transitions between overlapping images, and graffiti pigment identification all need colour-accurate photographs. Even if hard to achieve outdoors (Verhoeven, 2016), INDIGO expects to do better than anyone has accomplished so far. Since colour is a function of incoming radiation, the latter is measured for every photographed graffito with a spectrometer. ...
Graffiti is a short-lived form of heritage balancing between tangible and intangible, offensive and pleasant. Graffiti makes people laugh, wonder, angry, think. These conflicting traits are all present along Vienna's Donaukanal (Eng. Danube Canal), a recreational hotspot – located in the city's heart – famous for its endless display of graffiti. The graffiti-focused heritage science project INDIGO aims to build the basis to systematically document, monitor, and analyse circa 13 km of Donaukanal graffiti in the next decade. The first part of this paper details INDIGO's goals and overarching methodological framework, simultaneously placing it into the broader landscape of graffiti research. The second part of the text concentrates on INDIGO's graffiti documentation activities. Given the project's aim to create a spatially, spectrally, and temporally accurate record of all possible mark-makings attached in (il)legal ways to the public urban surfaces of the Donaukanal, it seems appropriate to provide insights on the photographic plus image-based modelling activities that form the foundation of INDIGO's graffiti recording strategy. The text ends with some envisioned strategies to streamline image acquisition and process the anticipated hundreds of thousands of images.
... Spatial resolution for photogrammetry can be defined as the Ground Sample Distance (GSD), given as a real-world measurement of the distance between two pixel centers in an image, which is determined by a combination of the sensor size, pixel size, focal length, and the distance of the camera from the surface ( GSD cannot be equated to the size of the smallest visible detail in the image, as two pixels do not provide enough information to be understood by the human eye. The smallest feature of interest should be captured with at least four pixels across its width (i.e. the GSD of a 1mm wide crack, should be at least one-fourth the width of the crack, or 0.25mm/pixel) (Verhoeven, 2016). 2 ...
In the field of wall painting conservation, photogrammetric surveys are an increasingly common documentation tool. The outputs from these surveys, including captured images, orthophotos, and three-dimensional models, are used by conservators to monitor and record condition phenomena and conservation treatments. To serve these conservation needs, the outputs should have visual fidelity, meaning they are a close representation of the subject based on their spatial resolution, overall focus, even lighting and color accuracy. However, wall paintings present unique technical challenges for photogrammetry considering their often large scale, irregular topography, range of surface attributes, and access issues. As a documentation technique more commonly applied to capture the geometry of buildings and objects, using photogrammetry to record both the topography and fine surface details of a wall painting requires thorough planning. This paper examines specific challenges in documenting wall paintings and how collaboration between conservators and heritage-recording specialists has improved practice and maximized the value of photogrammetric surveys for conservation.
... However, there is no standard procedure for this and it would be highly subjective. We will not elaborate on this aspect further, other than by remarking that during such a subjective assessment the art object should be lighted with the same light that was assumed in the camera pro ling (i.e., D50 spectrum), and the image would need to be visualized on a color calibrated monitor display (page 231 of [19]). ...
The growing importance of publishing art collections online has led to increasingly strict tolerances on digital photography of art objects. There are two internationally recognized sets of guidelines for creating high-quality digital images, Metamorfoze and FADGI.
These guidelines require using sets of standardized color patches in museal photography. The X-Rite ColorChecker SG chart with 140 color patches is often used. Recent studies showed that even in the standardized conditions of museum photography studios it is often very difficult to satisfy the strictest guidelines on color accuracy for camera profiling, with no indications for improvements.
Here we report results of our investigation into the bottlenecks in achieving high color accuracy. We show that a large part of the color deviations originates from the 15 black color patches of the ColorChecker SG chart. These patches have a large impact on the average color deviation and the maximum color deviation that are the performance measures for color accuracy in the FADGI and Metamorfoze guidelines. We show that spectrophotometer measurements for the black patches produce color deviations dE(CIE 1976) ranging from 3.7 to 5.2 with respect to reference data, making it impossible to meet the strictest Metamorfoze guidelines. The black patches push the average color difference CIEDE2000 from 0.59 to 0.82 with respect to reference data already when using spectrophotometer data. Since the strictest FADGI guidelines prescribe an average CIEDE2000=2.0, this leaves little tolerance for errors due to lighting and camera profile.
Our results indicate that the common practice of manually tweaking camera profiles until the software suggests sufficient color accuracy is obtained with respect to suppliers’ reference data often does not improve color representation but makes it worse, especially for representing dark nuances. This is unfortunate for example for the digital photography of 17th century Dutch paintings, where dark passages occupy large areas of the art works.
We show that the key step in achieving color accurate digital photography is to use customer reference data rather than commonly used generic reference data. We explain the results by investigating not only the color properties of the ColorChecker SG chart, but also its glossiness.
... Schematic representation of the most important EM bands for remote sensing applications[50,51]. The bands involved in this study are highlighted in yellow. ...
Historical architecture is a primary element containing the identity values of a society. The wide diffusion of many ancient buildings gathering part of these values on painting walls over territories often characterized by poor technological or economic resources brings to consider the development of low-cost protocols to inspect valued surfaces and to give the authorities in charge of preservation and restoration adequate technical information. Here we present the preliminary results of a recent application of remote sensing micro-geophysical techniques to typical architectural targets such as vaults. A modified commercial Digital Single-Lens Reflex (DSLR) camera was used to acquire multispectral datasets on portions of a painted vault. Multispectral datasets were used raw or after the application of a pre-processing step with a Multi Images Stacking (MIS) algorithm. Multispectral images were then processed with spatial wavelet decomposition, histogram enhancing, thresholds application, image fusion, false colors compositing and Principal Component Analysis (PCA) techniques. Software used have been GNU Image Manipulation Program (GIMP) and Mathworks MATLAB (which can be substituted for the processing steps proposed by the built-in functions of GNU OCTAVE open-source software). Processed images were able to highlight features on vault paintings revealing details of the surface or its very shallow layers which were impossible or very difficult to distinguish in raw data. In fact, they emphasized low-visible details, differences in apparently similar finishes or pigments, cracks and probably details of surface preparation.
... The bust of San Nicola da Tolentino was, therefore, the subject of a photographic campaign carried out first with a Canon EOS 5D Mark II professional camera (with Canon 24 mm fixed lens -f 1.4), then with a GoPro Hero 4 action camera and, finally, with an Apple I-Phone 7. In all cases, pictures were made by moving the instruments on an ideal sphere of constant radius and by directing the optic towards the centre of the statue. The first photographic survey campaign, made with professional instrumentation, followed a rigorous practice to obtain a photogrammetric 3D model of high metric and chromatic quality (Verhoeven, 2016;Torresani & Remondino, 2019). Photos were preceded by the calculation of both the depth of field and the hyperlocal distance, the control of the background noise and the compensation of the colour temperature of the ambient light by colour checker (fig. ...
The creation of three-dimensional models for the cataloguing and documentation of cultural heritage is today an emerging need in the cultural sphere and, above all, for museums. The cultural heritage is still catalogued and documented based on descriptive files assorted of photographic images which, however, fail to outline its spatial richness, possible only through the use of 3D artefacts. The essay aims to propose a methodology of digitalization by low-cost and easy-to-use systems, to be employed even by non-expert survey and photogrammetry’s operators. The case study of the statue of San Nicola da Tolentino, preserved at the Sant’Agostino complex in Bergamo, offered the possibility of a comparison between 3D models acquired with different digitalization tools (professional/action/amateur cameras and smartphone) and processed by several image-based 3D Reconstruction software and methods.
