Luminance

In this paper, we investigated the effects of dopants on the electrical and optical characteristics of dichromatic and white organic light-emitting devices (OLEDs) with a double emitting layer (DEML). Such a DEML consisted of two host materials with bipolar transport characteristics doped with two distinct types of phosphorescent emitters. The host for EML1 (adjacent to the anode side) was N,N-dicarbazolyl-3,5-benzene (mCP), with a hole mobility higher than the electron mobility, whereas the host for EML2 (adjacent to the cathode side) was 2,2 0-bis[5-phenyl-2-(1,3,4)oxadazolyl]biphenyl (OXD), with a higher electron mobility than the hole mobility. Phosphorescent blue emitters, 9% iridium(III)bis[4,6di-fluorophenyl-pyridinato-N,C2]picolinate (FIrpic), and phosphorescent green emitters, 9% fac-tris(phenylpyridine) iridium [Ir(ppy) 3 ], were doped into EML1 and EML2, respectively for dichromatic emission. In the dichromatic blue/green OLEDs, both the blue and green dopants helped to reduce the driving voltage. The dopants essentially played the role of carrier traps and recombination centers, from which the current density-voltage characteristics and electroluminescence (EL) spectra were derived. In this structure, EML1 and EML2 exhibited hole-and electron-rich bipolar transporting characteristics, respectively. Hence, the recombination was extended to the two EMLs, which reduced the efficiency roll-off and resulted in high efficiency levels even at high luminance levels. Through further incorporation of 0.5% of tris(2-phenylquinoline)iridium(III) [Ir(2-phq) 3 ] into EML1, a white OLED with maximum current efficiency of 35.8 cd/A and quantum efficiency of 10.73% at 0.643 mA/cm 2 was obtained. In this white OLED, the current efficiency decreased slightly by 2.51% from 35.8 cd/A at 230 cd/m 2 to 34.9 cd/A at 1000 cd/m 2. Carrier confinement was achieved at the D-EML interface, which not only contributed to the high current efficiency, but also resulted in stable color coordinates that varied a mere (À0.014, 0.004) from 100 to 10,000 cd/m 2 , without additional blocking layers between the two EMLs.

La necesidad manifiesta de mejorar los controles de acceso y seguridad han orientado el diseño de los nuevos sistemas de identificación personal hacia la utilización de rasgos biométricos, fisiológicos y comportamentales, que garanticen niveles de desempeño cada vez más altos. Con esta motivación, se presenta el desarrollo y evaluación de un sistema computacional para realizar los procedimientos de registro y validación de identidad de personas utilizando imágenes de las venas de la cara dorsal de la mano, compuesto por un módulo hardware de bajo costo para la adquisición de imágenes infrarrojas, utilizando una cámara de video convencional, lentes ópticos, fuentes de iluminación infrarroja controladas y un frame grabber; y un módulo software para la visualización y captura de las imágenes, selección de las regiones de interés, segmentación y extracción, descripción y clasificación de características. Finalmente, para evaluar la similitud entre las imágenes se implementa y evalúa una etapa basada en redes neuronales artificiales, permitiendo concluir que el indicador biométrico es lo suficientemente discriminante, y otra basada en correlación que, sobre una base de datos de 100 imágenes, determina la eficiencia máxima de sistema en 95,72% en un umbral igual a 65%, y 8,57% y 0% para las tasas de falsa aceptación (FAR) y falso rechazo (FRR) respectivamente. Palabras clave: sistemas de identificación personal, rasgos biométricos, registro y validación de identidad, procesamiento de imágenes, reconocimiento de patrones.

This research investigates the luminance and the brightness field distribution of the microstructure of a light guiding plate (LGP) by micro injection molding (MIM) and micro injection-compression molding (MICM). The process of manufacturing a LGP includes photo-etching, MIM, MICM, and optical field measurement. The results show that the luminance of microstructure of LGPs produced using MICM is better than those made using MIM. The results also indicate that the most important processing parameter is the mold temperature for the luminance distribution of the LGP whether made by MIM or MICM. The maximum luminance of the LGP is 80 Nit (cd/m 2 ) on micro molding. The brightness field distribution of the LGP made using MICM is more uniform than those made using MIM for the same processing parameters. MICM is a more suitable process than MIM for the fabrication of a LGP on a backlight panel (BLP).

We describe a psychophysical method for assessing binocular integration using dichopticallypresented uniform fields. By temporally modulating uniform field luminances at different frequencies between the eyes, a rhythmic bear is produced-a visual percept characterized by undulations in luminance at a frequency equal to the arithmetic difference between the two monocular stimulus frequencies. Using a signal detection paradigm, we studied the beat as a function of modulation depth in normal and binocularly deficient subjects. Normal subjects easily detected the beat, even at low modulation depths, while stereoblind subjects (with stereoacuity worse than 2OOOsec arc) failed to detect beats at any modulation depth or with any combination of stimulus frequencies tested. The beat provides evidence for the confluence of monocular signals into binocular integrating mechanisms. Our results therefore suggest that the status of functioning binocular mechanisms is related to the detectability of the beat. This uniform-field stimulus does not require accurate accommodation, fixation, vergence or high spatial resolution, thus making this technique particularly attractive for the study of binocular interaction in developing infants and in binocularly deficient adults. Binocular interaction Beats Psychophysics Amblyopia Nonlinear mechanisms Uniform fields Temporal

The present study was undertaken to evaluate the CIE overcast sky model for Japan using the data now emerging from the CIE International Daylight Measurement Programme. Kyushu University in Japan is the national and international coordinating centre for this programme. Using data from only those days which experienced a complete overcast it has been shown herein that the above model always underestimates the average vertical illuminance. The analysis indicates that a uniform sky is a better representation of the overcast luminance distribution.

Most multi-camera systems assume a well structured environment to detect and track objects across cameras. Cameras need to be fixed and calibrated, or only objects within a training data can be detected (e.g. pedestrians only). In this work, a master-slave system is presented to detect and track any objects in a network of uncalibrated fixed and mobile cameras. Cameras can have non-overlapping field-of-views. Objects are detected with the mobile cameras (the slaves) given only observations from the fixed cameras (the masters). No training stage and data are used. Detected objects are correctly tracked across cameras leading to a better understanding of the scene.

A high luminance contrast between windows and surrounding surfaces can increase the risk of discomfort glare, which can diminish office workers' satisfaction and productivity. Accordingly, it can lead to occupant interventions, such as drawing window blinds or increasing electric light levels, which are intended to enhance indoor visual comfort but counterproductively act to increase energy consumption. Increasing the luminance of the areas surrounding the windows using a supplementary lighting system, such as wall-washing with light emitting diode (LED) linear luminaires, could reduce discomfort glare arising from windowed walls. This paper reports on the results of a study in a typical office room in Brisbane, Australia. The outcomes of this study indicate that creating a luminance contrast of between 11:1 and 12:1 on the window wall in an office room with a 45% window-to-exterior-wall ratio using a supplementary LED system leads to improved subjective assessments of window appearance. The results suggest that such an enhancement could significantly reduce discomfort glare from windows, as well as diminishing the likelihood of the users intending to turn on the ceiling lights or to move the blinds.

In this paper, we present a novel no-reference (NR) method to assess the quality of JPEG-coded images using a sequential learning algorithm for growing and pruning radial basis function (GAP-RBF) network. The features for predicting the perceived image quality are extracted by considering key human visual sensitivity factors such as edge amplitude, edge length, background activity and background luminance. Image quality estimation involves computation of functional relationship between HVS features and subjective test scores. Here, the functional relationship is approximated using GAP-RBF network. The advantage of using sequential learning algorithm is its capability to learn new samples without affecting the past learning. Further, the sequential learning algorithm requires minimal memory and computational effort. Experimental results prove that the prediction of the trained GAP-RBF network does emulate the mean opinion score (MOS). The subjective test results of the proposed metric are compared with JPEG no-reference image quality index as well as full-reference structural similarity image quality index and it is observed to outperform both.

The SrAl 2 O 4 :Eu 2þ phosphor powders have been synthesized by sol-gel process. Electroluminescent (EL) properties of the SrAl 2 O 4 :Eu 2þ phosphor were investigated using a convenient thick film device. Green light emitting at a peak of 508 nm was obtained when driven by sine alternating current (AC). The color coordinate of the emission was x ¼ 0:148 and y ¼ 0:635: Luminance -voltage and afterglow characteristics of the SrAl 2 O 4 :Eu 2þ EL devices were studied. The results show that SrAl 2 O 4 :Eu 2þ can be used as green phosphor for EL displays. q

We compared the visual detection thresholds for cone-isolating stimuli of trichromats (those with normal color vision) with those of X-linked dichromats, who lack either the long-wavelength-sensitive (L) cones (protanopes) or middle-wavelengthsensitive (M) cones (deuteranopes). At low (1 Hz) temporal frequencies, dichromats have significantly higher (twofold) thresholds for all colored stimuli than trichromats; whereas at high (16 Hz) temporal frequencies, they perform as well or better than trichromats. The advantages of dichromats in detecting high temporally modulated targets can be related to an increased number, through replacement, of the remaining L-or M-cone type. However, their disadvantages in detecting low temporally modulated targets, even in directions of color space where their increased number of cone photoreceptors might be expected to be beneficial, are best explained in terms of the loss of LYM cone opponency and the inability of the visual pathways to reorganize to allow the detection of low-frequency luminance modulation.

Imaging in scattering media such as fog and water is important but challenging. Images suffer from poor visibility due to backscattering and signal attenuation. Most prior methods for scene recovery use active illumination scanners (structured and gated), which can be slow and cumbersome. On the other hand, natural illumination is inapplicable to dark environments. The current paper addresses the need for a non-scanning recovery method, that uses active scene irradiance. We study the formation of images under widefield artificial illumination. Based on the formation model, the paper presents an approach for recovering the object signal. It also yields rough information about the 3D scene structure. The approach can work with compact, simple hardware, having active widefield, polychromatic polarized illumination. The camera is fitted with a polarization analyzer. Two frames of the scene are instantly taken, with different states of the analyzer or light-source polarizer. A recovery algorithm follows the acquisition. It allows both the backscatter and the object reflection to be partially polarized. It thus unifies and generalizes prior polarization-based methods, which had assumed exclusive polarization of either of these components. The approach is limited to an effective range, due to image noise and falloff of widefield illumination. Thus, these limits and the noise sensitivity are analyzed. The approach particularly applies underwater. We therefore use the approach to demonstrate recovery of object signals and significant visibility enhancement in underwater field experiments.

Vision-based tracking is a basic elementary task in many computer vision-based applications such as video surveillance and monitoring, sensing and navigation in robotics, video compression, video annotation, and many more. However, reliable recovery of targets and their trajectories in an uncontrolled environment is affected by a wide range of conditions exhibited by the environment such as sudden illumination changes and clutter. This work addresses the problem of (i) combining information from a set of cues in order to obtain reasonably accurate estimates of multiple targets in uncontrolled environments and (ii) a collection of data association methods for cues containing less information for robust tracking through persistent clutter. Specifically, we introduce a novel geometric template constrained data association method for robust tracking of point features, while using the Joint Probabilistic Data Association (JPDA) method for blob cue measurements. Extensive experimental validation of the tracking and the data association framework is presented in the work for several real-world outdoor traffic intersection image sequences.

This paper presents an efficient solution for digital images sharpening, the Adaptive Directional Sharpening with Overshoot Control (ADSOC), a method based on a high-pass filter able to perform a stronger sharpening in the detailed zones of the image, preserving the homogeneous regions. The basic objective of this approach is to reduce the undesired effects. The sharpening introduced along strong edges

We present compact illumination engines for DMD projection systems making use of light emitting diodes (LEDs) as light sources. The impact of uniformization optics and color-combining dichroic filters is investigated with respect to the color uniformity on the screen. PhlatLight LEDs are considered as light sources because of their superior luminance levels. Also PhotonVacuum optics are used to collimate and transform the emitted LED light distribution. The optical engines are simulated with advanced non-sequential ray tracing software. They are evaluated on the basis ofétendue efficiency, compactness and color uniformity of the projected images. Color plots are used as tools to investigate the simulated color gradients in the image. To validate our simulation models, we have built a compact prototype LED projector. Its color-related specifications are compared with the simulated values. Downloaded from SPIE Digital Library on 13 May 2010 to 91.179.92.45. Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7723 77230X-2 Downloaded from SPIE Digital Library on 13 May 2010 to 91.179.92.45. Terms of Use: http://spiedl.org/terms * DMD Discovery 3000 Proc. of SPIE Vol. 7723 77230X-9 Downloaded from SPIE Digital Library on 13 May 2010 to 91.179.92.45. Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7723 77230X-11 Downloaded from SPIE Digital Library on 13 May 2010 to 91.179.92.45. Terms of Use: http://spiedl.org/terms View publication stats View publication stats

Interest point detection is an important research area in the field of image processing and computer vision. In particular, image retrieval and object categorization heavily rely on interest point detection from which local image descriptors are computed for image matching. In general, interest points are based on luminance, and color has been largely ignored. However, the use of color increases the distinctiveness of interest points. The use of color may therefore provide selective search reducing the total number of interest points used for image matching.

Visual processing of color and luminance for smooth pursuit and saccadic eye movements was investigated using a target selection paradigm. In two experiments, stimuli were varied along the dimensions color and luminance, and selection of the more salient target was compared in pursuit and saccades. Initial pursuit was biased in the direction of the luminance component whereas saccades showed a relative preference for color. An early pursuit response toward luminance was often reversed to color by a later saccade. Observers' perceptual judgments of stimulus salience, obtained in two control experiments, were clearly biased toward luminance. This choice bias in perceptual data implies that the initial short-latency pursuit response agrees with perceptual judgments. In contrast, saccades, which have a longer latency than pursuit, do not seem to follow the perceptual judgment of salience but instead show a stronger relative preference for color. These substantial differences in target selection imply that target selection processes for pursuit and saccadic eye movements use distinctly different weights for color and luminance stimuli.

This paper presents a quantitative comparison of several segmentation methods (including new ones) that have successfully been used in traffic sign recognition. The methods presented can be classified into color-space thresholding, edge detection, and chromatic/achromatic decomposition. Our support vector machine (SVM) segmentation method and speed enhancement using a lookup table (LUT) have also been tested. The best algorithm will be the one that yields the best global results throughout the whole recognition process, which comprises three stages: 1) segmentation; 2) detection; and 3) recognition. Thus, an evaluation method, which consists of applying the entire recognition system to a set of images with at least one traffic sign, is attempted while changing the segmentation method used. This way, it is possible to observe modifications in performance due to the kind of segmentation used. The results lead us to conclude that the best methods are those that are normalized with respect to illumination, such as RGB or Ohta Normalized, and there is no improvement in the use of Hue Saturation Intensity (HSI)-like spaces. In addition, an LUT with a reduction in the less-significant bits, such as that proposed here, improves speed while maintaining quality. SVMs used in color segmentation give good results, but some improvements are needed when applied to achromatic colors.

Electrophysiological testing of the visual 8 system requires familiarity with photometry. This 9 technical note outlines the concepts of photometry 10 with a focus on information relevant to clinical ERG 11 and VEP testing. Topics include photometric quan-12 tities, consideration of pupil size, specification of 13 brief extended flash stimuli, and the influence of the 14 spectral composition of visual stimuli. Standard units 15 and terms are explained in the context of the ISCEV 16 standards and guidelines for clinical electrophysiol-17 ogy of vision. 18 Keywords Photometry Á ISCEV Á 19 Luminance Á Illuminance Á Flash Á 20 Clinical electrophysiology of vision Á 21 ERG Á VEP 22 23 24 ''We all know what light is; but it is not easy to 25 tell what it is.''

Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs Á optical excitation, Fö rster energy transfer, and direct charge injection Á that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desired color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs.

Of all the functions that define visual performance, the mesopic luminous efficiency function is probably the most complex and hardest to standardise or model. Complexities arise because of the substantial and often rapid visual changes that accompany the transition from scotopic to photopic vision. These are caused not only by the switch from rod to cone photoreceptors, but also by switches between different post-receptoral pathways through which the rod and cone signals are transmitted. In this review, we list several of the complexities of mesopic vision, such as rod-cone interactions, rod saturation, mixed photoreceptor spectral sensitivities, different rod and cone retinal distributions, and the changes in the spatial properties of the visual system as it changes from rod-to cone-mediated. Our main focus, however, is the enormous and often neglected temporal changes that occur in the mesopic range and their effect on luminous efficiency. Even before the transition from rod to cone vision is complete, a transition occurs within the rod system itself from a sluggish, sensitive post-receptoral pathway to a faster, less sensitive pathway. As a consequence of these complexities, any measure of mesopic performance will depend not only on the illumination level, but also on the spectral content of the stimuli used to probe performance, their retinal location, their spatial frequency content, and their temporal frequency content. All these should be considered when attempting to derive (or to apply) a luminous efficiency function for mesopic vision.

Vcan be found. Here, by using selective adaptation and/or tritanopic metamers to isolate the S-cone response, we investigate the dependence of the S-cone luminance input on changes in background wavelength and radiance. Interestingly, the S-cone luminance input disappears completely when no adapting background is present, even though the same S-cone stimulus makes a clear contribution to luminance when a background is present. The dependence of the S-cone luminance input on the wavelength and radiance of the adapting background is surprising. We find that the S-cone signal can be measured on fields of 491 nm and longer wavelengths that exceed a criterion background radiance. These criterion radiances roughly follow an L + M spectral sensitivity, which suggests that the S-cone luminance input is silent unless the L-and M-cones are excited above a certain level. We hypothesize that the L + M cone signals produced by the steady adapting backgrounds somehow "gate" the S-cone luminance signals, perhaps by being modulated by them.

Ten years ago Greenberg and colleagues presented their framework for realistic image synthesis , aiming "to develop physically based lighting models and perceptually based rendering procedures for computer graphics that will produce synthetic images that are visually and measurably indistinguishable from real-world images", paraphrasing Sutherland's 'ultimate display' . They specifically encouraged vision researchers to use natural, complex and three-dimensional (3D) visual displays to get a better understanding of human vision and to develop more comprehensive visual models for computer graphics that will improve the efficiency of algorithms. In this paper we follow Greenberg et al.'s directive and analyse colour and luminance gradients in a complex 3D scene. The gradients arise from changes in the light source position and orientation of surfaces. Information in image gradients could apprise the visual system about intrinsic surface reflectance properties or extrinsic illumination phenomena, including shading, shadowing and inter-reflections. Colour gradients induced by inter-reflection may play a similar role to that of luminance gradients in shape-from-shading algorithms; it has been shown that 3D shape perception modulates the influence of interreflections on surface colour perception ].

We present a tone reproduction operator that preserves visibility in high dynamic range scenes. Our method introduces a new histogram adjustment technique, based on the population of local adaptation luminances in a scene. To match subjective viewing experience, the method incorporates models for human contrast sensitivity, glare, spatial acuity, and color sensitivity. We compare our results to previous work and present examples of our techniques applied to lighting simulation and electronic photography.

LED-based projection systems have several interesting features: extended color-gamut, long lifetime, robustness and a fast turn-on time. However, the possibility to develop compact projectors remains the most important driving force to investigate LED projection. This is related to the limited light output of LED projectors that is a consequence of the relative low luminance of LEDs, compared to high intensity discharge lamps. We have investigated several LED projection architectures for the development of new 3D visualization displays. Polarization-based stereoscopic projection displays are often implemented using two identical projectors with passive polarizers at the output of their projection lens. We have designed and built a prototype of a stereoscopic projection system that incorporates the functionality of both projectors. The system uses high-resolution liquidcrystal-on-silicon light valves and an illumination system with LEDs. The possibility to add an extra LED illumination channel was also investigated for this optical configuration. Multiview projection displays allow the visualization of 3D images for multiple viewers without the need to wear special eyeglasses. Systems with large number of viewing zones have already been demonstrated. Such systems often use multiple projection engines. We have investigated a projection architecture that uses only one digital micromirror device and a LED-based illumination system to create multiple viewing zones. The system is based on the time-sequential modulation of the different images for each viewing zone and a special projection screen with micro-optical features. We analyzed the limitations of a LED-based illumination for the investigated stereoscopic and multiview projection systems and discuss the potential of a laser-based illumination.

The evolutionary and behavioral significance of an animal's color patterns remains poorly understood 1, 2, 3 and 4, not least, patterns that reflect ultraviolet (UV) light [5]. The current belief is that UV signals must be broad and bold to be detected because (1) they are prone to scattering in air and water, (2) when present, UV-sensitive cones are generally found in low numbers, and (3) long-wavelength-sensitive cones predominate in form vision in those species tested to date [6]. We report a study of two species of damselfish whose appearance differs only in the fine detail of UV-reflective facial patterns. We show that, contrary to expectations, the Ambon damselfish (Pomacentrus amboinensis) is able to use these patterns for species discrimination. We also reveal that the essential features of the patterns are contained in their shape rather than color. The results provide support for the hypothesis that UV is used by some fish as a high-fidelity “secret communication channel” hidden from predators 7 and 8. In more general terms, the findings help unravel the details of a language of color and pattern long since lost to our primate forebears, but which has been part of the world of many seeing organisms for millions of years.► Some species of reef fish possess complex UV-reflecting facial patterns ► The fish are able to use these patterns to perform species discrimination ► Unlike other animals, the fish can discriminate complex patterns using their S cones ► UV light offers a “secret communication channel,” unseen by UV-blind predators

Projectors are increasingly being used as lightsources in computer vision applications. In several applications, they are modeled as point light sources, thus ignoring the effects of illumination defocus. In addition, most active vision techniques assume that a scene point is illuminated only directly by the light source, thus ignoring global light transport effects. Since both defocus and global illumination co-occur in virtually all scenes illuminated by projectors, ignoring them can result in strong, systematic biases in the recovered scene properties. To make computer vision techniques work for general real world scenes, it is thus important to account for both these effects.

Starting with the experiments of Ramachandran and Gregory (Nature, 275, 55-56, 1978), several psychophysical studies in apparent motion (AM) have established that the perception of motion is significantly impaired at equiluminance. Still debated, however, is whether color alone can resolve ambiguities in AM. We report here on several psychophysical experiments, the quantitative results of which indicate that color does play a substantial role in AM. These findings seem to support recently proposed neurophysiological frameworks according to which there exist significant interactions among the neuronal pathways mediating the perception of basic visual attributes such as color, motion, form and depth.

Two novel word clustering techniques are proposed which employ long distance bigram language models. The first technique is built on a hierarchical clustering algorithm and minimizes the sum of Mahalanobis distances of all words after a cluster merger from the centroid of the class created by merging. The second technique resorts to probabilistic latent semantic analysis (PLSA). Next, interpolated long distance bigrams are considered in the context of the aforementioned clustering techniques. Experiments conducted on the English Gigaword corpus (second edition) demonstrate that: (1) the long distance bigrams, when employed in the two clustering techniques under study, yield word clusters of better quality than the baseline bigrams; (2) the interpolated long distance bigrams outperform the long distance bigrams in the same respect; (3) the long distance bigrams perform better than the bigrams, which incorporate trigger-pairs selected at various distances; and (4) the best word clustering is achieved by the PLSA that employs interpolated long distance bigrams. Both proposed techniques outperform spectral clustering based on k-means. To assess objectively the quality of the created clusters, relative cluster validity indices are estimated as well as the average cluster sense precision, the average cluster sense recall, and the F-measure are computed by exploiting ground truth extracted from the WordNet.

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com". Machine Vision and Applications (2014) 25:985-995

In a texture-segregation paradigm, subjects were asked to detect figures whose elements were segregated from background either because of temporal offset or because of differing orientations. Texture elements were either isoluminant or had high or low luminance contrast. At high luminance contrast, figures could be segregated both on the basis of orientation and temporal cues whereby temporal offsets as short as 10 msec supported detection. At isoluminance, orientation defined figures were as readily distinguishable as in the high contrast condition but temporally defined figures were perceived only for offset intervals >50 msec. With low luminance contrast, performance for orientation defined figures was impaired relative to the high contrast condition, but for temporally defined figures, it was superior to the isoluminant condition; detection was possible for offset intervals as short as 22 msec. These results suggest that the temporal and orientation cues which support scene segmentation are transmitted by both the luminance and colour sensitive pathways. However, if temporal offsets are < 50 msec, segmentation of temporally defined figures is supported only by the luminance sensitive system. © 1997

All municipalities in Sweden offer their inhabitants a service for disposing of large-size and hazardous waste at local recycling centres. Opening hours at these centres include hours of darkness. The aims of this study were to 1) describe user and employee experiences of lighting and signs at Swedish recycling centres, 2) measure and assess the lighting system at the two recently built recycling centres in Linkö ping and to assess the legibility and visibility of the signs used and 3) propose recommendations regarding lighting and signs for recycling centres. Interviews and questionnaires were used to assess experiences of employees and users, and light measurements were performed. By observing users, activities with different visual demands at different areas within the recycling centres were identified. Based on the literature, standards and stakeholder experiences, recommendations regarding lighting systems and sign design, illuminance, luminance and uniformity are proposed for recycling centres.

In the present experiment we addressed the question of how the visual system determines surface lightness from luminances in the retinal image. We measured the perceived lightness of target surfaces that were embedded in custom-made checkerboards. The checkerboards consisted of 10 by 10 checks of 10 different reflectance values that were arranged randomly across the board. They were rendered under six viewing conditions including plain view, with a shadow-casting cylinder, or with one of four different transparent media covering part of the board. For each reflectance we measured its corresponding luminance in the different viewing conditions. We then assessed the lightness matches of four observers for each of the reflectances in the different viewing conditions. We derived predictions of perceived lightness based on local luminance, Michelson contrast, edge integration, anchoring theory, and a normalized Michelson contrast measure. The normalized contrast measure was the best predictor of surface lightness and was almost as good as the actual reflectance values. The normalized contrast measure combines a local computation of Michelson contrast with a region-based normalization of contrast ranges with respect to the contrast range in plain view. How the segregation of image regions is accomplished remains to be elucidated.

In many cases, it is not possible to faithfully capture shadow and highlight image data of a high dynamic range (HDR) scene using a common digital camera, due to its narrow dynamic range (DR). Conventional solutions tried to solve the problem with an captured image which has saturated highlight and/or lack of shadow information. In this situation, we introduce a color image enhancing method with the scene-adaptive exposure control. First, our method recommends an optimal exposure to obtain more information in highlight by the histogram-based scene analysis. Next, the proposed luminance and contrast enhancement is performed on the captured image. The main processing consists of luminance enhancement, multi-band contrast stretching, and color compensation. The luminance and chrominance components of input RGB data is separated by converting into HSV color space. The luminance is increased using an adaptive log function. Multi-band contrast stretching functions are applied to each sub-band to enhance shadow and highlight at the same time. To remove boundary discontinuities between sub-bands, the multi-level low-pass filtering is employed. The blurred image data represents local illumination while the contrast-stretched details correspond to reflectance of the scene. The restored luminance image is produced by the combination of multi-band contrast stretched image and multilevel low-pass filtered image. Color compensation proportional to the amount of luminance enhancement is applied to make an output image.

Purpose -The purpose of this paper is to develop a robot vision system for surface defect detection of 3D objects. It aims at the ill-defined qualitative items such as stains and scratches. Design/methodology/approach -A robot vision system for surface defect detection may counter: high surface reflection at some viewing angles; and no reference markers in any sensed images for matching. A filtering process is used to separate the illumination and reflection components of an image. An automatic marker-selection process and a template-matching method are then proposed for image registration and anomaly detection in reflection-free images. Findings -Tests were performed on a variety of hand-held electronic devices such as cellular phones. Experimental results show that the proposed system can reliably avoid reflection surfaces and effectively identify small local defects on the surfaces in different viewing angles. Practical implications -The results have practical implications for industrial objects with arbitrary surfaces. Originality/value -Traditional visual inspection systems mainly work for two-dimensional planar surfaces such as printed circuit boards and wafers. The proposed system can find the viewing angles with minimum surface reflection and detect small local defects under image misalignment for three-dimensional objects.

This paper is a study of the influences of the different parameters which affect the photometric evaluation of light-emitting surfaces (due to reflection or self-emission) when a conventional color digital camera is used. The overall purpose of this paper is to evaluate the luminance and the reflectivity of the vertical traffic sign with the camera in order to provide an automatic recognition of deteriorated reflective sheeting material of which the traffic signs were made. This paper describes how the A/D converter output signal given by a pixel of the digital camera can be related to the luminance and the reflectivity of the corresponding surface element whose image is formed on a pixel. Thus, each surface element of the traffic sign's surface can be separately evaluated. By photometrically calibrating the camera, we have been able to prove this relationship in our experiments.

We propose a new technique for fusing multiple cues to robustly segment an object from its background in video sequences that suffer from abrupt changes of both illumination and position of the target. Robustness is achieved by the integration of appearance and geometric object features and by their estimation using Bayesian filters, such as Kalman or particle filters. In particular, each filter estimates the state of a specific object feature, conditionally dependent on another feature estimated by a distinct filter. This dependence provides improved target representations, permitting us to segment it out from the background even in nonstationary sequences. Considering that the procedure of the Bayesian filters may be described by a "hypotheses generationhypotheses correction" strategy, the major novelty of our methodology compared to previous approaches is that the mutual dependence between filters is considered during the feature observation, that is, into the "hypotheses-correction" stage, instead of considering it when generating the hypotheses. This proves to be much more effective in terms of accuracy and reliability. The proposed method is analytically justified and applied to develop a robust tracking system that adapts online and simultaneously the color space where the image points are represented, the color distributions, the contour of the object, and its bounding box. Results with synthetic data and real video sequences demonstrate the robustness and versatility of our method.

Attending selectively to changes in our visual environment may help filter less important, unchanging information within a scene. Here, we demonstrate that color changes can go unnoticed even when they occur throughout an otherwise static image. The novelty of this demonstration is that it does not rely upon masking by a visual disruption or stimulus motion, nor does it require the change to be very gradual and restricted to a small section of the image. Using a two-interval, forcedchoice change-detection task and an odd-one-out localization task, we showed that subjects were slowest to respond and least accurate (implying that change was hardest to detect) when the color changes were isoluminant, smoothly varying, and asynchronous with one another. This profound change blindness offers new constraints for theories of visual change detection, implying that, in the absence of transient signals, changes in color are typically monitored at a coarse spatial scale.

We present techniques for the processing of color, high-dynamic luminance images of a type aiming for objectivity and also of a type aiming for aesthetic improvement. In the first case we start with camera raw data, propose a variant white balance, darken very light spots and lighten very dark spots. In the second case we use color spaces of the type hue-saturation-luminance; we propose a hue processing method inspired in the Bezold-Brucke effect as well as a luminance-dependant displacement of color saturation.

This study investigates the contribution of color vision to global motion. We present evidence demonstrating that performance on a global motion task attains similar levels for both types of chromatic (L/M-cone opponent and Scone opponent) and luminance stimuli at suprathreshold contrasts. We show, however, that the motion thresholds for isoluminant chromatic stimuli are luminance based, on the grounds that they are masked by luminance noise but robust to chromatic noise. Detection thresholds, on the other hand, are chromatic in origin (masked by chromatic but not luminance noise), indicating that there is no luminance artifact in the stimulus. We suggest that for color vision at isoluminance the global motion task is based on the integration of many local, luminance-based signals.