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Unmanned aerial vehicles with hyperspectral sensors present new opportunities for acquiring imagery in overcast conditions. Under such conditions, the empirical line method, with targets of known reflectance can be used for atmospheric compensation. Therefore, understanding changes in spectral response from lab, to field and UAV conditions is important. We assess four standard reference targets (2%-50% reflectance) that were initially characterized in the laboratory. Then, we assess their reflectance derived from field spectroscopy measurements and UAV hyperspectral imagery under diffuse illumination field conditions. In-scattering from surrounding vegetation and high attenuation of the SWIR were found in field-based spectra. Resampled laboratory spectra show good correspondence with UAV HSI spectra of the panels., IGARSS 2021: 2021 IEEE International Geoscience and Remote Sensing Symposium, July 11-16, 2021, Brussels, Belgium

Newts can use spatial variation in the magnetic field (MF) to derive geographic position, but it is unclear how they detect the ‘spatial signal’, which, over the distances that newts move in a day, is an order of magnitude lower than temporal variation in the MF. Previous work has shown that newts take map readings using their light-dependent magnetic compass to align a magnetite-based ‘map detector’ relative to the MF. In this study, time of day, location and light exposure (required by the magnetic compass) were varied to determine when newts obtain map information. Newts were displaced from breeding ponds without access to route-based cues to sites where they were held and/or tested under diffuse natural illumination. We found that: (1) newts held overnight at the testing site exhibited accurate homing orientation, but not if transported to the testing site on the day of testing; (2) newts held overnight under diffuse lighting at a ‘false testing site’ and then tested at a site located in a different direction from their home pond oriented in the home direction from the holding site, not from the site where they were tested; and (3) newts held overnight in total darkness (except for light exposure for specific periods) only exhibited homing orientation the following day if exposed to diffuse illumination during the preceding evening twilight in the ambient MF. These findings demonstrate that, to determine the home direction, newts require access to light and the ambient MF during evening twilight when temporal variation in the MF is minimal.

Purpose: Limbal ischemia is an important prognostic factor in the management of ocular burns. In this study, we evaluated the reliability of clinically assessing limbal ischemia among ophthalmic professionals. Methods: This study included 111 ophthalmic professionals who were shown 12 diffuse illumination color slit-lamp photographs of eyes with recent chemical injuries. Respondents were asked whether the photos were assessable and if yes, then to indicate the presence, location, and grade of limbal ischemia in each case. The responses were collected using a standard data collection sheet and the inter-observer agreement was calculated. Results: All participants responded to every question. Of the 1,332 responses, images were deemed assessable in 1,222 (91.7%) instances. The overall agreement (Fleiss' kappa) for the presence of limbal ischemia and severity of limbal ischemia was 0.106 and 0.139, respectively (P < 0.012). Among the four groups of observers, practicing cornea specialists displayed significantly (P < 0.003) higher kappa values (0.201–0.203) when compared to residents (0.131–0.185), fellows (0.086–0.127), and optometrists (0.077–0.102). All indicated a poor level of inter-rater consistency. Conclusion: The results indicate that clinical assessment of limbal ischemia is highly subjective and there is lack of reliability even among cornea specialists who regularly manage patients with ocular burns. A non-invasive, standardized, objective, accurate, and reliable modality for ocular surface angiography is desperately needed for proper assessment and prognostication of ocular burns.

Dye-sensitized solar cells (DSSCs), as emerging photovoltaic technology, have been thoroughly and extensively investigated in the last three decades. Since their first appearance in 1991, DSSCs have gained increasing attention and have been classified as feasible alternatives to conventional photovoltaic devices due to their numerous advantages, such as cheap and simple preparation methods, the possibility of being integrated in buildings and astonishing performances under indoor and diffuse illumination conditions. Photoconversion efficiencies of up to 14% and 8% have been obtained for lab-scale devices and modules, respectively. Albeit the efforts made, these values seem arduous to be outdone, at least under simulated solar radiation. Nevertheless, recent lab-scale systems have demonstrated photoconversion efficiencies of up to 33% under indoor illumination (i.e. 1000 lux) leading to an actual Renaissance (or Revival) of these devices. It is worth mentioning that scientists in this field are developing innovative materials aiming at long-term and efficient devices, being the concept of sustainability often set apart. However, in light of effective commercialization of this technology, stability, efficiency and sustainability should be considered as the essential keywords. Nowadays, DSSCs are finding a “new way back” towards sustainability and rather a huge number of reports have focused on the preparation of green and cost-effective materials to replace the standard ones. In this scenario, the present review aims to give an overview of the most adopted strategies to enhance the sustainability of materials in classical DSSC components (e.g. sensitizer, redox couple, electrolyte and counter-electrode), including smart synthesis and deposition procedures, which currently represent utmost important topics in the scientific community.

Cambial activity records short and long-term environmental signals in xylem anatomy, creating a permanent archive. Quantitative wood anatomy deciphers the relationship between cell structure and function in a spatiotemporal context. Obtaining high-resolution images of wood anatomical preparations is a critical stage in the process of decoding this information. Damage to cellular structures when sectioning by microtome is one of the main problems in the preparation of high-quality micro-sections. Cell damage leads to the occurrence of artifacts – most often related to broken cell walls – hindering the performance of image recognition programs, and increasing the time spent on the manual editing of images. In this work, we propose an alternative method to microtomy, based on embedding-polishing protocols established for hard tissue preparation. Wood samples are embedded in a transparent and non-reactive resin as polymethylmethacrylate (PMM) that is subsequently ground and polished. Being able to acquire images from the stained or unstained polished surfaces of the PMM-blocks and sections (thinner than 100 μm) by using a wide range of optical methods such as reflected polarizing microscopy, epifluorescence microscopy, bright-field microscopy with diffuse illumination and circularly polarizing microscopy. This embedding method improves the mechanical integrity and quality of wood anatomical preparations, eliminating the problem of broken cell walls. Furthermore, this technique allows the preparation and analysis of large tissue surfaces.

In this paper, the perceived blackness of 10 specific automotive finishes with different levels of orange peel attribute is investigated under the diffuse illumination condition. Since the purchased ACT black panels had approximately the same colorimetric attributes, i.e., lightness, hue, and chroma, the effect of colorimetric properties on perceived blackness was minimized. Thirty nonexpert observers including 14 males and 16 females were selected to compare the blackness perception of ACT black panels. The observers’ normal color vision was already evaluated by applying the Ishihara test method. The black panels were ranked from the minimum perceived blackness to the maximum by employing the pair comparison method and performing 1800 visual assessments. Results showed that, in general, the blackness perception of panels increased with a decrease in their orange peel attributes, but the orange peel attribute is not the only factor affecting the perceived blackness of black panels. Besides, while the black panels were colorimetrically too close to each other, the panel with the lowest lightness and chroma value was assessed as the blackest sample among the ACT panels with the lowest orange peel attribute.

Pavement marking is an essential task of road construction and maintenance. Pavement markings are beneficial because they provide information regarding the road alignment and road conditions ahead. To fully utilize their benefits, the retroreflectivity (RL30) and diffuse illumination (QD30) of pavement markings need to be above a minimum threshold. The degradation of RL30 and QD30 depends on several factors, such as the traffic exposure, age of the pavement marking, and weather. This research investigated the reflective efficiency of thermoplastics on an asphaltic concrete pavement marking with a glass bead rate of 359 to 553 grams per square meter. The reflective data were collected at the beginning of a period of eight months at two-week intervals. The factors that have a statistically significant effect on the pavement marking RL30 and QD30 include the traffic exposure and pavement marking position. The dirt coating on top of the marking is the most crucial factor that temporarily deteriorates the retroreflectivity, which can recover to some degree by rainfall.

Summary Countershading was one of the first proposed mechanisms of camouflage [1, 2]. A dark dorsum and light ventrum counteract the gradient created by illumination from above, obliterating cues to 3D shape [3, 4, 5, 6]. Because the optimal countershading varies strongly with light environment [7, 8, 9], pigmentation patterns give clues to an animal’s habitat. Indeed, comparative evidence from ungulates [9] shows that interspecific variation in countershading matches predictions: in open habitats, where direct overhead sunshine dominates, a sharp dark-light color transition high up the body is evident; in closed habitats (e.g., under forest canopy), diffuse illumination dominates and a smoother dorsoventral gradation is found. We can apply this approach to extinct animals in which the preservation of fossil melanin allows reconstruction of coloration [10, 11, 12, 13, 14, 15]. Here we present a study of an exceptionally well-preserved specimen of Psittacosaurus sp. from the Chinese Jehol biota [16, 17]. This Psittacosaurus was countershaded [16] with a light underbelly and tail, whereas the chest was more pigmented. Other patterns resemble disruptive camouflage, whereas the chin and jugal bosses on the face appear dark. We projected the color patterns onto an anatomically accurate life-size model in order to assess their function experimentally. The patterns are compared to the predicted optimal countershading from the measured radiance patterns generated on an identical uniform gray model in direct versus diffuse illumination. These studies suggest that Psittacosaurus sp. inhabited a closed habitat such as a forest with a relatively dense canopy. Video Abstract, Graphical Abstract Image 1, Highlights • Preserved pigments in the dinosaur Psittacosaurus suggest countershading camouflage • We predicted the optimal countershading camouflage for different light environments • The dinosaur’s patterns would have been cryptic in a forest, but not open, habitat • We can also infer that dinosaur predators used shape-from-shading cues to detect prey, Countershading camouflage uses a dark-to-light gradient from back to belly to counter the light-to-dark gradient created by illumination. The body appears flatter and less conspicuous. Vinther et al. use 3D reconstruction and radiance modeling to show that the dinosaur Psittacosaurus was countershaded and cryptic in a forested environment.

International audience; The different areas of a concave object illuminate each other by a multiple light reflection process, called interreflections, depending on the geometries of the object and the lighting. For an accurate prediction of the radiance perceived from each point of the object by an observer or a camera, an interreflection model is necessary, taking into account the optical properties and the shape of the object, the orientation(s) of the incident light which can produce shadows, and the infinite number of light bounces between the different points of the object. The present paper focusses on the irradiance of two adjacent planar panels (V-cavity) illuminated by collimated light from any direction of the hemisphere, or by diffuse light. According to the reflectance of the material and the angle of the cavity, the loss of irradiance near the fold due to the shadowing effect is partly compensated by the gain in radiance due to the interreflections.

12 pags., 7 figs., Effect pigments in coatings produce eye-catching colour and texture effects and are widely used in automotive, cosmetics, coatings, inks, flooring, textile or decoration. One of these texture effects is graininess, which is the perceived texture exhibited when the effect coating is observed under diffuse illumination. To date there is not a standard procedure to measure graininess from reflectance measurements. The objective of this work is to propose a methodology for traceable graininess measurements, similarly as it was proposed for colour in 1931. In this article, the relevant reflectance-based quantities are clearly defined, and a formal relation with data from visual experiments is given. This methodology would allow a measurement scale of graininess and a difference formula to be agreed once conclusive visual data become available., The EMPIR is jointly funded by the EMPIR participating countries within EURAMET and the European Union. Part of the authors (Instituto de Óptica “Daza de Valdés” (IO, CSIC), Agencia Estatal CSIC) are also grateful to Comunidad de Madrid for funding the project SINFOTON-CM: S2013/MIT-2790. Part of the authors (Color & Vision Group, University of Alicante) are also grateful to Spanish Ministry of Economy and Competitiveness for funding the project ADIREVGAO: DPI2015-65814-R.

The blackness perception of six black automotive finishes was evaluated under three different illumination conditions: unidirectional illumination, diffuse illumination and light booth condition. The metallic black panels with approximately the same appearance attributes, specular gloss, distinctness of image and orange peel, were selected to minimize the effect of total appearance factors on perceived blackness. Fourteen non-expert observers (5 males and 9 females) assessed the black panels while their normal color vision was examined by the Ishihara test. The pair comparison method was applied to rank the metallic black panels based on their perceived blackness. The results showed that under the diffuse illumination condition, a good correlation was observed between the lightness attribute of metallic black panels and their visual scales, where a decrease of the L* value leads to an increase of perceived blackness. In addition, observers assessed the darkest and the most neutral panel as the blackest sample under the three applied illumination conditions.

Hemispherical diffuse illumination is a common ambient lighting environment. We highlight the unique issues related to measuring the ambient performance of curved displays under hemispherical diffuse illumination, and propose methods to address them. A flexible reflective e-paper display (EPD) is measured inside an integrating sphere, and comparison made to the sampling sphere method. The EPD is measured not only in its flat state, but also when bent to cylindrical shapes of various radii of curvature.

International audience; We present a photometric stereo-based system for retrieving the RGB albedo and the fine-scale details of an opaque surface. In order to limit specularities, the system uses a controllable diffuse illumination, which is calibrated using a dedicated procedure. In addition, we rather handle RAW, non-demosaiced RGB images, which both avoids uncontrolled operations on the sensor data and simplifies the estimation of the albedo w.r.t. each color channel and of the normals. We eventually show on real-world examples the potential of photometric stereo for the 3D-reconstruction of very thin structures from a wide variety of surfaces.

Viewing direction measurements on reflective e-paper displays under hemispherical diffuse illumination are an essential part of characterizing reflectance under common usage conditions such as outdoor shade, or indirect indoor lighting. This paper proposes a hemispherical diffuse illumination geometry based on splitting a sampling sphere into two hemispheres to allow the light measuring device to be pointed at the display at different angles. First results on e-paper agree well with conventional sampling sphere data, show the effects of top layer and surface reflection, and were used to predict the viewing direction distribution of ambient contrast ratio.

This paper presents a collection of tools for aiding the design and system simulations of fixed and mobile photovoltaic energy harvesting systems. The presented tools help to estimate the available power, and to study the requirements of the maximum power point tracking. The effects caused by panel self-heating and active bypassing in series connected panel systems are studied.

We introduce embodied lenses for visual queries on tabletop surfaces using physical interaction. The lenses are simply thin sheets of paper or transparent foil decorated with fiducial markers, allowing them to be tracked by a diffuse illumination tabletop display. The physical affordance of these embodied lenses allow them to be overlapped, causing composition in the underlying virtual space. We perform a formative evaluation to study users’ conceptual models for overlapping physical lenses. This is followed by a quantitative user study comparing performance for embodied versus purely virtual lenses. Results show that embodied lenses are as efficient as purely virtual lenses, and also support tactile and eyes-free interaction. We then present several examples of the technique, including image layers, map layers, image manipulation, and multidimensional data visualization. The technique is simple, cheap, and can be integrated into many existing tabletop displays.

The accumulation of multiple redox equivalents is essential in photo-driven catalytic reactions such as solar water splitting. However, direct spectroscopic observation of a twice-oxidized species under diffuse illumination has proved elusive until now.

People readily perceive smooth luminance variations as being due to the shading produced by undulations of a 3-D surface (shape-from-shading). In doing so, the visual system must simultaneously estimate the shape of the surface and the nature of the illumination. Remarkably, shape-from-shading operates even when both these properties are unknown and neither can be estimated directly from the image. In such circumstances humans are thought to adopt a default illumination model. A widely held view is that the default illuminant is a point source located above the observer’s head. However, some have argued instead that the default illuminant is a diffuse source. We now present evidence that humans may adopt a flexible illumination model that includes both diffuse and point source elements. Our model estimates a direction for the point source and then weights the contribution of this source according to a bias function. For most people the preferred illuminant direction is overhead with a strong diffuse component.

Interactive surfaces are only just beginning to break into the market, and they still do not offer the advanced functionality demonstrated with many lab prototypes. The path from a prototype system to a finished product for use in real-world scenarios is a long one, and many obstacles must be overcome. The design of an interactive multitouch table had to address issues like optical recognition, hardware design, and ergonomics. This paper describes in detail the construction of a large, robust multi-touch table called mrT. It will show how to solve major problems of the diffuse illumination technique and other challenges of constructing a large-screen, high-resolution, self-contained interactive multitouch surface that not only serves as a development system but can be deployed in the real-world. Additionally, to further motivate some of the design decisions, especially why the diffuse illumination technology was chosen, this paper will discuss related on-going research projects on the application side.

We propose a new method to calibrate the HXMT collimators by measuring the optical point spread function (PSF) of the hard X-ray modulation telescope (HXMT). The light transmission of the collimator at different viewing angles with a camera and a diffuse backlight placed behind the collimator is measured. This method is much easier to accomplish than measuring the PSF with a parallel optical beam. The experimental results are very consistent with the simulations. The PSF of the collimator of the high energy X-ray telescope on HXMT is found to be in good agreement with the design, with accuracy better than 1 arcmin.

Direct estimation of photosynthetic light-use efficiency (LUE) from space would be of significant benefit to LUE-based models which use inputs from remote sensing to estimate terrestrial productivity. The Photochemical Reflectance Index (PRI) has shown promise in tracking LUE at the leaf- to small canopy levels, but its use at regional to global scales still remains a challenge. In this study, we used different formulations of PRI calculated from the MODIS ocean band centered at 531 nm and a set of alternative reference bands at 488, 551, and 678 nm to explore the relationship between PRI and LUE where LUE was measured at eight eddy covariance flux towers located in the boreal forest of Saskatchewan, Canada. The magnitude and variability of LUE was significantly lower at the times when useful MODIS ocean band images were available (i.e. around midday under clear-sky conditions) relative to the rest of the growing season. PRI678 (reference band at 678 nm) showed the strongest relationship (r2 = 0.70) with LUE90a (i.e. 90-minute mean LUE calculated using Absorbed Photosynthetically Active Radiation, APAR), but only when all sites were combined. Overall, the relationships between the MODIS PRIs and LUE90a were always stronger for observations closer to the backscatter direction and there were no significant differences in the strength of the correlations whether LUE was calculated based on incident PAR or on APAR. Predictions of ecosystem photosynthesis at the time of the MODIS overpasses were significantly improved by multiplying either PAR or APAR by MODIS PRI (r2 improved from 0.09 to 0.44 and 0.54 depending on the PRI formulation). We used our PRI-LUE model to create a regional LUE90a map for the three cover types covering 47,500 km2 around the flux sites. The MODIS PRI-derived LUE90a map appeared to capture more realistic spatial heterogeneity of LUE across the landscape compared to a daily LUE map derived using the look-up table in the MODIS GPP (MOD17) algorithm. While our LUE map is only a snapshot of minimum regional LUE90a values, with appropriate gap-filling methods it could be used to improve regional-scale monitoring of GPP. Moreover, the strong relationship between midday and daily LUE on clear days (r2 = 0.93) indicates that instantaneous MODIS observations of LUE90a could be used to estimate daily LUE. Finally, pixel shadow fraction from the 5-Scale geometric-optical model was closely related to both MODIS PRI and tower-derived LUE suggesting that differences in stand leaf area and in diffuse illumination among flux sites play a role in the relationship we observed between LUE and MODIS PRI.

We present a novel method to retrieve multiple positions of point lights in real indoor scenes based on a 3D reconstruction. This method takes advantage of illumination over planes detected using a segmentation of the reconstructed mesh of the scene. We can also provide an estimation without suffering from the presence of specular highlights but rather use this component to refine the final estimation. This allows consistent relighting throughout the entire scene for aumented reality purposes.

Statement of problem Clinically relevant assessment of all-ceramic crowns supported by esthetic composite resin foundations has not been evaluated with regard to color reproducibility. Purpose This in vitro study quantitatively evaluated the influence of different shades of composite resin foundations and resin cement on the final color of a leucite-reinforced all-ceramic material. Material and methods A total of 128 disks were fabricated; 64 (20 × 1 mm) were made of all-ceramic material (IPS Empress) and 64 (20 × 4 mm) of 4 different shades composite resin (Tetric Ceram). The ceramic and composite resin disks were luted using 2 shades (A3 and Transparent) of resin cement (Variolink II). Color was measured using a colorimeter configured with a diffuse illumination/0-degree viewing geometry, and Commission Internationale de l'Eclairage (CIE) L ∗ a ∗ b ∗ values were directly calculated. Descriptive statistical analysis was performed, and color differences (ΔE) for the average L ∗ , a ∗ and b ∗ color parameters were calculated. Repeated measures analysis of variance (ANOVA) was used to compare mean values and SDs between the different color combinations (α=.05). Results The CIE L ∗ a ∗ b ∗ color coordinate values showed no significant differences for variation in color parameters due to the effect of the different composite resin shades ( P =.24) or cement shades ( P =.12). The mean color difference (ΔE) value between the groups was 0.8. Conclusion Within the limitations of this study, the use of different shades for composite resin cores and resin cements presented no statistically significant effect on the final color of IPS Empress all-ceramic material.

We present a technique which uses existing OpenGL capabilities to approximate the effect of blurry specular reflections and indirect diffuse illumination. It makes use of environment maps, mipmapping with level of detail control, and possibly texture borders. The method is extremely simple to implement, in some cases requiring just a single additional OpenGL statement.

Summary Effective study of in situ stained sections often requires illumination that is difficult to achieve with commonly used research microscopes. One must be able to switch quickly and conveniently from the very lowest to moderate magnifications. At all magnifications contrast due to light scatter must be minimized, so that the weak staining that signifies low gene expression can be observed reliably. For the lowest power objectives (e.g., 1.25× or 2×) many microscopes require that the condenser be removed to illuminate the full field of view. This is not only very inconvenient when switching magnifications, but without a condenser the low numerical aperture of the illuminating light beam results in unwanted contrast due to light scatter. We have devised a simple system that diffusely illuminates the full field of view of the lowest power objective (1.25×) and has high enough numerical aperture for use with the 25× and 40× objectives. A key feature is the use of a large diameter ring light (internal diameter 5.8 cm), placed on the microscope base, to illuminate a large diameter diffuser placed just below the slide.

The geometric conditions of diffuse illumination, 8 degree observation, specular light include (SCI) and specular light exclude (SCE) often be employed to measure the surface color of material with different gloss value. The SCE condition is usually realized by setting light trap on the integrating sphere. However, the structure of light trap has its negative influence on the light intensity uniformity, and can led to the inaccuracy of the test results under SCE or SCI condition. Due to the different sizes of the light trap, structures of the measurement instrument will led to inter instrument agreement among the measurement of sample with different gloss. This paper designs a measuring structure to measure the SCE and SCI results simultaneously; proposes a method to calculate the 8 degree gloss value based on the SCE and SCI test result; proposes a computing modal to modify the SCI and SCE measure result based on the 8 degree gloss value, experimental verifying is also carried out. The experimental results demonstrate the structure and modified model effectively reduce the negative influence of light trap. The inter instrument disagreement caused by the geometric dimension of different light trap is significantly decreased.

Iris illumination typically causes specular highlighting both within the pupil and iris. This lighting variation is intended to be masked in the preprocessing stage. By removing or reducing these specular highlights, it is thought that a more accurate template could be made, improving the matching results. In an attempt to reduce these specular highlights we propose a diffuse illumination system. To determine if iris recognition performance is enhanced by this diffuse illumination system, we examine whether specular highlights were reduced within the pupil and iris, as well as analyze matching results obtained by several iris algorithms.

An analysis in the Fresnel approximation is given of the formation conditions of lateral-shear holographic interferograms in bands of infinite width characterizing the wave aberrations of a microscope optical system over the field in the case of coherent diffuse illumination of a ground-glass screen.

Purpose To evaluate the influence of a diffuse illumination device located outside the field of vision that provokes a controlled pupillar miosis, on the visual acuity and contrast sensitivity in drivers tested in mesopic conditions Methods Cross-sectional prospective observational study in which visual Acuity 100% and 20% contrast by ETDRS Test (VA100 and VA20) and Contrast Sensitivity by Pelli-Robson Test (CS) were evaluated in 39 drivers individuals under 40 years old and 30 drivers over 40. The study was carried out in a simulated setting for night driving with and without the interposition of the diffuse illumination device Results In individuals aged over 40 years, an statistically significant improvement of visual function was exhibit. Baseline visual acuity and contrast sensitivity scores were: VA100=0.02±0.18logMAR, VA20=0.21±0.2logMAR, and CS=0.62±0.32, whereas values for the interposition of diffuse illumination device were: VA100=-0.03±0.14logMAR(p=0.02), VA20=0.19±0.17logMAR(p=0.3), and CS=0.76±0.33(p=0.0003). On the other hand, in drivers aged under 40, statistically significance was not found. In this condition, baseline visual function was: VA100=-0.1±0.11logMAR, VA20=0.13±0.19logMAR, and CS=1.06±0.2, whereas the interposition of the mentioned system showed the following values: VA100=0.01±0.09logMAR(p=0.9), VA20=0.09±0.14logMAR(p=0.3), and CS=1.08±0.16(p=0.6) Conclusion Using diffuse illumination device in the interior of the vehicle, provides significant improvement in both high contrast visual acuity and contrast sensitivity in the group older than 40 years

In this paper, we present an approach for sensing object shapes and touching of interactive tables based on diffuse illumination (DI) and frustrated total internal reflection (FTIR) and other infrared-based tracking approaches. Our approach uses tangible objects with series connection of optical fibers as bend and touch sensors. The approach enables detection of object deformations and touched points on the object with no modification of the original tabletop-based tracking system. We present the basic concept and an initial evaluation of the approach.

In the physical world we use both hands in a very distinctive manner. Much research has been dedicated to transfer this principle to the digital realm, including multi-touch interactive surfaces. However, without the possibility to reliably distinguish between hands, interaction design is very limited. We present an approach for enhancing multitouch systems based on diffuse illumination with left and right hand distinction. Using anatomical properties of the human hand we derive a simple empirical model and heuristics that, when fed into a decision tree classifier, enable real-time hand distinction for multi-touch applications.

Fast and accurate touch detection is critical to the usability of multi-touch tabletops. In optical tabletops, such as those using the popular FTIR and DI technologies, this requires efficient and effective noise reduction to enhance touches in the camera's input. Common approaches to noise reduction do not scale to larger tables, leaving designers with a choice between accuracy problems and expensive hardware. In this paper, we present a novel noise reduction algorithm that provides better touch recognition than current alternatives, particularly in noisy environments, without imposing higher computational cost. We empirically compare our algorithm to other noise reduction approaches using data collected from tabletops at research labs in Canada and Europe.

Multi-touch interaction with computationally enhanced surfaces has received considerable attention in recent years. Hardware implementations of multi-touch interaction such as Frustrated Total Internal Reflection (FTIR) and Diffuse Illumination (DI) have allowed for the low cost development of surfaces. Although many of these technologies and associated applications have been presented in academic settings, the practicalities of building a high quality multi-touch enabled surface, both in terms of the software and hardware required, are not widely known. We draw upon our extensive experience as developers of multi-touch technology to provide practical advice in relation to building, and deploying applications upon, multi-touch surfaces. This includes technical details of the construction of optical multi-touch surfaces, including: infrared illumination, silicone compliant surfaces, projection screens, cameras, filters, and projectors, and an overview of existing software libraries for tracking.

A method to numerically remove the twin image for inline digital holography, using multiple digital holograms, is discussed. Each individual hologram is recorded by using a statistically independent speckle field to illuminate the object. If the holograms are recorded in this manner and then numerically reconstructed, the twin image appears as a different speckle pattern in each of the reconstructions. By performing speckle-reduction techniques the presence of the twin image can be greatly reduced. A theoretical model is developed, and experimental results are presented that validate this approach. We show experimentally that the dc object intensity term can also be removed by using this technique.

Ambient occlusion (AO) is a lighting model that approximates the diffuse illumination of a surface based on its directly visible occluders. It can be rendered by tracing rays through the normal-oriented unit hemisphere, and returning the percentage of rays that do no hit any geometry at a distance d

We describe a mathematical and algorithmic study of Shape From Shading problem for scenes illuminated by ambient lighting. The ambient lighting is here modelled by a (whole) spherical light source of infinite radius centered on the object of interest. The mathematical formulation of this problem results in resolving a strongly non-local and non-linear Integro-Partial Differential Equation (I-PDE). The first contribution of this report is to provide a first theoretical study of this global I-PDE, when previous theoretical works only deal with a local version obtained by ignoring the shadow, i.e. the occlusion of the light field by the surface itself. We give a comparison result in the C^1 space which allows to characterize the set of the solutions. The second contribution consists in providing a monotonic, consistent and stable approximation scheme for the I-PDE which, according to Barles and Souganidis' theory, classically ensures the correctness of the numerical approximations. We then explain how to implement the associated numerical algorithm and show and discuss about some numerical results. Contrary to our previous conference paper, this technical report contains the detailed proofs of all stated theorems.; Nous présentons une première étude mathématique et un premier algorithme numérique rigoureux pour le problème du ''Shape From Shading'' dans le cas d'une scène éclairée uniquement par un éclairage ambiant (diffus). L'éclairage ambiant est ici modélisé par une source de lumière sphérique de rayon infini et centrée sur l'objet d'intérêt. La formulation mathématique de ce problème aboutit à la résolution d'une équation intégro-différentielle (équation aux dérivées partielles contenant un terme intégral) fortement non locale et non linéaire. Ce travail s'illustre par ses deux principales contributions. 1) Tout d'abord, nous fournissons une première étude théorique de cette équation globale, alors que les travaux théoriques précédents se limitaient à une version locale obtenue en ignorant les ombres portées, c'est à dire en ignorant les occlusions du champ de lumière par la surface elle même. Plus précisément, nous formulons un résultat de comparaison qui permet de caractériser les solutions de classe C^1. 2) Ensuite nous fournissons un premier algorithme numérique qui vérifie rigoureusement les propriétés classiques de convergence (stabilité, cohérence, monotonie) développées par Barles et Souganidis. Nous expliquons ensuite comment implémenter notre algorithme et nous analysons quelques exemples de résultats numériques.