Relative Luminance Research Articles

Focusing on mixed narrow band stimuli: Implications for mechanisms of accommodation and displays.

The eye has considerable chromatic aberration, meaning that the accommodative demand varies with wavelength. Given this, how does the eye accommodate to light of differing spectral content? Previous work is not conclusive but, in general, the eye focuses in the center of the visible spectrum for broadband light, and it focuses at a distance appropriate for individual wavelengths for narrowband light. For stimuli containing two colors, there are also mixed reports. This is the second of a series of two papers where we investigate accommodation in relation to chromatic aberrationFernandez-Alonso, Finch, Love, and Read (2024). In this paper, for the first time, we measure how the eye accommodates to images containing two narrowband wavelengths, with varying relative luminance under monocular conditions. We find that the eye tends to accommodate between the two extremes, weighted by the relative luminance. At first sight, this seems reasonable, but we show that image quality would be maximized if the eye instead accommodated on the more luminous wavelength. Next we explore several hypotheses as to what signal the eye might be using to drive accommodation and compare these with the experimental data. We show that the data is best explained if the eye seeks to maximize contrast at low spatial frequencies. We consider the implication of these results for both the mechanism behind accommodation, and for modern displays containing narrowband illuminants.

The role of extrinsic and intrinsic factors in perceptual filling-in of the blind-spot with variegated color and texture stimuli

Vision scientists dedicated their efforts to unraveling the mechanism of filling-in at the blind-spot (BS) through numerous psychophysical experiments. The prevalent interpretation, emphasizing active filling-in, has spurred extensive research endeavors. In a parallel vein, a pertinent study highlighted the predominance of the nasal Visual Field (VF) over the temporal one and postulated the role of the Cortical Magnification Factor (CMF) in explaining the asymmetry of filling-in. In this study, we first replicated this experiment and then conducted BS-specific psychophysical experiments employing various bi-colored and bi-textured (patterned) stimuli. We observed that nasal dominance is not persistent in the context of the spread of perception for BS filling-in. We posit that the visual information processing priority index (VIPPI), comprising the CMF (an intrinsic factor unaffected by stimulus characteristics) and relative luminance (an extrinsic factor dependent on stimulus characteristics), governs the spread of perception for filling-in in case of diverse neighborhoods of the BS.

High-performance black electrochromic devices using benzothiadiazole viologen and trisaminocyclopropenium perchlorate with extremely low transmittance and good stability

To minimize the colored state transmittance of the device in the ultraviolet–visible (UV–Vis) region (300–800 nm), we applied the idea of spectral complementary absorption to design electrochromic devices with transparent to black transition. Benzothiadiazole viologen (BV) and trisaminocyclopropenium ions (TAC) organic materials with dark blue and red coloration states were selected to prepare electrochromic devices with extremely low transmittance, here TAC is used as electrochromic material for the first time. The electrochromic devices do not require any supporting electrolytes. By controlling the concentration ratio of two materials, we achieved the ultra-low transmittance (0.33%), extremely low relative luminance (%YL = 0.12%), and fairly high coloring efficiency (341.9 cm2/C) of the TB-1 (0.05 mol/L TAC, 0.05 mol/L BV) device. Meanwhile, the TB-2 (0.0375 mol/L TAC, 0.05 mol/L BV) device possesses high transmittance contrast (81.79%) and very good long-cycle stability (4000 cycles, 96.1%).

Relative luminance of ambiguous figure/ground regions impacts the ability of the watercolor illusion to bias figure assignment

Relative luminance of ambiguous figure/ground regions impacts the ability of the watercolor illusion to bias figure assignment

84‐4: Switchable Privacy LCD Suitable for the Automotive Super Long‐Size Screen

We have developed a Switchable Privacy FFS LCD that can be switched between two display modes: 1) Public mode with wide viewing profile and 2) Privacy mode activated partially only in CDD area. By adopting the new LCD configuration, our 12.3‐ inch prototype has successfully enabled: 1) Seamless Public mode and 2) Privacy mode that lowers the relative luminance (<1.3%) over H‐25deg, and 3) Minimized color difference (Δxy<0.005) between modes.

Development of a Low-Cost Luminance Imaging Device with Minimal Equipment Calibration Procedures for Absolute and Relative Luminance

Luminance maps are information-dense measurements that can be used to directly evaluate and derive a number of important lighting measures, and improve lighting design and practices. However, cost barriers have limited the uptake of luminance imaging devices. This study presents a low-cost custom luminance imaging device developed from a Raspberry Pi microcomputer and camera module; however, the work may be extended to other low-cost imaging devices. Two calibration procedures for absolute and relative luminance are presented, which require minimal equipment. To remove calibration equipment limitations, novel procedures were developed to characterize sensor linearity and vignetting, where the accurate characterization of sensor linearity allows the use of lower-cost and highly non-linear sensors. Overall, the resultant device has an average absolute luminance error of 6.4% and an average relative luminance error of 6.2%. The device has comparable accuracy and performance to other custom devices, which use higher-cost technologies and more expensive calibration equipment, and significantly reduces the cost barrier for luminance imaging and the better lighting it enables.

Method for characterizing small-spot luminance in medical virtual reality headsets

We present an experimental method that utilizes a conic probe attached to an integrating sphere for characterizing the small-spot luminance of virtual reality (VR) head-mounted displays (HMDs). This allows for the measurement of relative luminance in virtual scenes and the assessment of VR displays for visualizing grayscale medical images. We characterized the relative luminance of the VIVE Pro and Oculus Rift by displaying test patterns with a circular dark spot of varying diameter in the bright field and compared the probe performance with commercially available systems. Compared to a conventional flat-panel display, the results show a significant level of veiling glare in the HMDs using both a customized conic probe with improved optical performance and an advanced imaging photometer. We also found no significant change in the relative luminance response with the probe’s working distance for the HMDs due to their unique optical architecture for near-eye viewing conditions. Our results highlight the issue of high veiling glare in HMDs and the importance of small-spot luminance measurements to adequately evaluate the technical performance of HMDs for emerging medical applications.

Is there no beauty in sexually dimorphic eyes? Facial attractiveness and White Europeans ocular morphology-Brief communication.

The link between human ocular morphology and attractiveness, especially in the context of its potential adaptive function, is an underexplored area of research. In our study, we examined the association between facial attractiveness and three sexually dimorphic measures of ocular morphology in White Europeans: the sclera size index, width-to-height ratio, and relative iris luminance. Sixty participants (30 women) assessed the attractiveness of the opposite-sex photographs of 50 men and 50 women. Our results show that in both men and women, none of the three measures was linked to the opposite sex ratings of facial attractiveness. We conclude that those ocular morphology measures may play a limited role in human mate preferences.

Improved Cherenkov Imaging across a Wide Range of Skin Pigmentation Levels for the Inclusion of Diverse Patient Populations

<h3>Purpose/Objective(s)</h3> Cherenkov imaging has recently emerged as a tool to visualize radiation dose and detect treatment incidents in real-time. The principle relies on the proportionality between Cherenkov light emission and dose deposited within tissue, introducing an additional opportunity to use the image information as a 2D surface dose map. The Cherenkov-dose relationship is affected by tissue optical properties, and recent studies have utilized routine CT-scans to correct for optical attenuation due to fibroglandular and adipose tissues, and blood volume, in the breast. However, the bulk of the reported <i>in vivo</i> data is limited to light-skinned patients due to limitations of geographical demographics. It is well documented that melanin is an optical absorber of Cherenkov photons, yet no prior <i>in vivo</i> work has been done to characterize the effect of different skin tones on Cherenkov dosimetry. We hypothesize that skin color information can be used to correct Cherenkov images for optical attenuation relating to melanin absorption across a diverse patient population. <h3>Materials/Methods</h3> A multi-institutional partnership was developed aiming to collect data from a more diverse patient population. A time-gated, intensified CMOS camera installed in the ceiling of a treatment room collects Cherenkov images of breast RT patients during their treatment. A standard color camera module is mounted adjacent to the Cherenkov camera to collect a color background image. Following a process developed with phantom studies, the two images are co-registered together in post-processing, RGB values are extracted from the skin over the treatment regions to calculate the relative skin luminance, L, and this value is compared to the optical emission from the corresponding Cherenkov image. A linear regression model is then used to assess the proportionality between L and Cherenkov emission intensity. <h3>Results</h3> The Cherenkov imaging system is being deployed in a clinic with a catchment area demographic of 67.4% Non-Hispanic White, an increase in diversity from 89.4% at the home institution. A clear relationship exists between skin color information and Cherenkov intensity, which cannot be determined like the bulk tissue properties from the CT scan alone. We found that L, derived from a wide range of melanin concentrations, is linearly proportional to Cherenkov intensity (R² = 0.98). Each Cherenkov image can be corrected based on skin luminance to improve the Cherenkov-dose relationship across various skin types. <h3>Conclusion</h3> The effect of both inter- and intra-patient skin color variations on the Cherenkov intensity can be corrected by using a linear regression model to increase the linearity between Cherenkov and deposited dose. This work will be used to improve our current CT-correction algorithm for all skin types and presents a major step towards expanding the inclusivity of Cherenkov imaging as a dosimetric tool for every patient.

Estimating Sheet Flow Velocities Using Quinine as a Fluorescent Tracer: Bare, Mulched, Vegetated and Paved Surfaces

When direct flow velocity measurements are not feasible, the use of tracers can be a valuable tool. In the present study, both laboratory and field experiments were conducted to evaluate the applicability of quinine as a fluorescent tracer for estimating mean sheet flow velocities in different ambient light and surface morphology conditions. Quinine excels in low-light conditions when exposed to UVA light. This tracer was compared with dye and thermal tracers, all in liquid form. In these tracing techniques the tracers were injected into the flow, after which surface velocity was estimated by tracking the leading edge of the tracer plumes and applying a correction factor to calculate the mean velocity (in a water column). The visibility of the tracers was evaluated by measuring the relative luminance and contrast ratio of the quinine and dye tracer plumes. Results show that the quinine tracer can be used to estimate sheet flow velocities over a wide variety of soil and urban surfaces; it has better visibility in comparison to the dye tracer but, in some conditions, lower visibility than the thermal tracer. Although quinine is invisible under bright ambient light conditions, this tracer technique requires low-cost experimental setup and is useful in low-light conditions (e.g., night; twilight; shielded environments).

Cortical mechanisms of visual brightness.

SUMMARYThe primary visual cortex signals the onset of light and dark stimuli with ON and OFF cortical pathways. Here, we demonstrate that both pathways generate similar response increments to large homogeneous surfaces and their response average increases with surface brightness. We show that, in cat visual cortex, response dominance from ON or OFF pathways is bimodally distributed when stimuli are smaller than one receptive field center but unimodally distributed when they are larger. Moreover, whereas small bright stimuli drive opposite responses from ON and OFF pathways (increased versus suppressed activity), large bright surfaces drive similar response increments. We show that this size-brightness relation emerges because strong illumination increases the size of light surfaces in nature and both ON and OFF cortical neurons receive input from ON thalamic pathways. We conclude that visual scenes are perceived as brighter when the average response increments from ON and OFF cortical pathways become stronger.

Preview the Products on Display at Display Week 2022

Preview the Products on Display at Display Week 2022

Scalable Reflective Plasmonic Structural Colors from Nanoparticles and Cavity Resonances – the Cyan‐Magenta‐Yellow Approach

AbstractPlasmonic metasurfaces for color generation are emerging as important components for next generation display devices. Fabricating bright plasmonic colors economically and via easily scalable methods, however, remains difficult. Here, the authors demonstrate an efficient and scalable strategy based on colloidal lithography to fabricate silver‐based reflective metal–insulator–nanodisk plasmonic cavities that provide a cyan‐magenta‐yellow (CMY) color palette with high relative luminance. With the same basic structure, they exploit different mechanisms to efficiently produce a complete subtractive color palette. Finite‐difference time‐domain simulations reveal that these mechanisms include gap surface plasmon modes for thin insulators and hybridized modes between disk plasmons and Fabry–Pérot modes for thicker systems. To produce yellow hues, they take advantage of higher‐energy gap surface plasmon modes to allow resonance dips in the blue spectral region for comparably large nanodisks, thereby circumventing difficult fabrication of nanodisks less than 80 nm. It is anticipated that incorporation of these strategies can reduce fabrication constraints, produce bright saturated colors, and expedite large‐scale production.

Sky luminance distribution model based on the information method and ant colony system

This study presents a novel model to estimate the sky luminance distribution (SLD) using the information method based on the research results of the SLD and atmospheric optics theory. The ant colony system of complex optimisation heuristic algorithms is used to analyse and optimise the influencing factors of sky luminance. The SLD using the information method is universal and is not related to geographical, latitudinal or climatic conditions. First, a simple and clear sky classification method is proposed. Then, a model framework is constructed. Using the ant colony system, the effects of the sky luminance elements are analysed and optimised, and numerical expressions for the coefficients of the relative luminance distribution are obtained. Finally, the proposed model is compared with other sky models (Perez’s model, the Commission Internationale de l’Eclairage model and Igawa’s all-sky model). The results show that the proposed model offers significant advantages for generating a universal SLD. Moreover, the information method SLD model can significantly enrich the coverage of the reference sky, and it avoids the shortcomings of existing sky models.

Correlations between powder wettability and part colour in the High Speed Sintering process

High Speed Sintering (HSS) is a powder bed fusion additive manufacturing technology that relies on inkjet printing of an infrared (IR) radiation absorbing material (RAM) onto a polymer powder bed in order to produce cross-sections which can be selectively sintered using an IR lamp. The RAM used in HSS is carbon black, which is suspended in a petroleum-based carrier fluid to form an ink. The use of carbon black in this way means that any parts currently produced by HSS are inevitably some shade of black or grey depending on the amount and distribution of RAM on the part surface. As well as affecting aesthetics, the effect of printing different densities of RAM has previously been shown to influence part sintering and subsequently mechanical properties, which demonstrates the importance of RAM distribution in determining the final properties of parts made using HSS. Anecdotally, it has also been observed that parts produced with the same type, amount and printed density of ink, but using different polymer powders, can be significantly different colours. This suggests that the wetting interaction between the ink and the polymer powder is also significant factor in determining the distribution of RAM on a part surface. However, to date there has been no investigation into the nature of this relationship. By measuring part colour, in this work we quantify differences in RAM distribution when different polymers are processed via HSS using the same printed density of ink, with parts made from commercially available powders of poly(propylene) (PP), pol(ether-b-amide) (PEBA), poly(styrene) (PS), poly(amide)-11 (PA11), and poly(amide)-12 (PA12) having Relative Luminance (i.e. brightness) of (5.3 ± 0.2)%, (5.5 ± 0.5)%, (12 ± 1)%, (15 ± 2)%, and (18 ± 1)%, respectively. The contact angles of the ink on the powder beds were measured in a simple model system, and these were found to be (46.1 ± 0.8)°, (80 ± 3)°, 82°, (90 ± 2)°, and (93 ± 2)° for PP, PEBA, PS, PA11, and PA12, respectively. With the exception of one anomalous data point for PEBA, it is demonstrated that part Relative Luminance can be correlated to contact angle, and that we can describe that relationship to good precision using a semi-empirical model. Knowledge about the effect of ink wettability on RAM distribution should prove useful for continuing the optimisation of the parts obtained by HSS.

Luminance Attentive Networks for HDR Image and Panorama Reconstruction

AbstractIt is very challenging to reconstruct a high dynamic range (HDR) from a low dynamic range (LDR) image as an ill‐posed problem. This paper proposes a luminance attentive network named LANet for HDR reconstruction from a single LDR image. Our method is based on two fundamental observations: (1) HDR images stored in relative luminance are scale‐invariant, which means the HDR images will hold the same information when multiplied by any positive real number. Based on this observation, we propose a novel normalization method called “HDR calibration “for HDR images stored in relative luminance, calibrating HDR images into a similar luminance scale according to the LDR images. (2) The main difference between HDR images and LDR images is in under‐/over‐exposed areas, especially those highlighted. Following this observation, we propose a luminance attention module with a two‐stream structure for LANet to pay more attention to the under‐/over‐exposed areas. In addition, we propose an extended network called panoLANet for HDR panorama reconstruction from an LDR panorama and build a dualnet structure for panoLANet to solve the distortion problem caused by the equirectangular panorama. Extensive experiments show that our proposed approach LANet can reconstruct visually convincing HDR images and demonstrate its superiority over state‐of‐the‐art approaches in terms of all metrics in inverse tone mapping. The image‐based lighting application with our proposed panoLANet also demonstrates that our method can simulate natural scene lighting using only LDR panorama. Our source code is available at https://github.com/LWT3437/LANet.

Comparative Evaluation of Mineral Trioxide Aggregate Obturation Using Four Different Techniques-A Laboratory Study.

This study aimed to compare the density of mineral trioxide aggregate (MTA) as a root canal filling material in the apical 5 mm of artificial root canals. Forty transparent acrylic blocks with 30-degree curved canals were instrumented and allocated into four compaction technique groups (n = 10): Lawaty (hand files); gutta-percha (GP) points; auger (nickel–titanium rotary files in reverse mode); and plugger technique. Filled canals were weighed after setting the MTA to calculate difference in mass. Two postoperative radiographs compared radiopacity by measuring luminance variations at 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm from the root apex. Obturation time was measured using a digital chronometer. The significance level was set to p < 0.05. The plugger group had a lower mass. Relative luminance was significantly higher for the Lawaty group than the plugger group at all examined apical levels. The relative luminance of the auger and GP groups were significantly higher than the plugger group at depths between 0.5 mm and 2 mm. Relative luminance was highest for the Lawaty technique at all depths between 0.5 mm and 4 mm. The Lawaty technique group was associated with increased obturation time compared with pluggers. Compacting MTA in curved canals with the Lawaty technique has the highest mass and radiopacity but requires more time.

Attractiveness in the Eyes: A Possibility of Positive Loop between Transient Pupil Constriction and Facial Attraction.

Contrary to the long-held belief of a close linkage between pupil dilation and attractiveness, we found an early and transient pupil constriction response when participants viewed an attractive face (and the effect of luminance/contrast was controlled). While human participants were making an attractiveness judgment on faces, their pupil constricted more for the more attractive (as-to-be-rated) faces. Further experiments showed that the effect of pupil constriction to attractiveness judgment extended to intrinsically esthetic visual objects such as natural scene images (as well as faces) but not to line-drawing geometric figures. When participants were asked to judge the roundness of faces, pupil constriction still correlated with their attractiveness but not the roundness rating score, indicating the automaticity of the pupil constriction to attractiveness. When pupillary responses were manipulated implicitly by relative background luminance changes (from the prestimulus screen), the facial attractiveness ratings were in accordance with the amount of pupil constriction, which could not be explained solely by simultaneous or sequential luminance contrast. The overall results suggest that pupil constriction not only reflects but, as a part of self-monitoring and attribution mechanisms, also possibly contributes to facial attractiveness implicitly.

Investigating Human Perception of Head‐Up Display Ghosting

AbstractUnlike wedge windshield technology that mitigates HUD image ghosting by reducing the ghost disparity angle, P‐pol combiner film windshields improve image quality by reducing the relative ghost luminance (RGL). Initial survey data indicate that this approach produces mostly imperceptible ghosting and high‐quality, legible images, and confirms that the RGL metric must be included along with the disparity angle when evaluating HUD ghosting.

Luminance and saliency have impact on pedestrians’ fixation distribution during natural walking: Evidence from mobile eye-tracker

The general environmental factors that influence fixation distribution as part of pedestrian visual behaviour under natural conditions are unclear. Relative luminance and saliency are considered the parameters for predicting image-based fixation; however, they are not confirmed by evidence from the natural walking scenario. Field experiments using mobile eye-tracking glasses device were conducted on 16 participants in four commercial streets during day and night. Fixation data along with processed images extracted from eye-tracking glass video were analysed to investigate if relative luminance or saliency correlates with fixation distribution while walking. The results show that fixations within a 10° viewing angle were distributed in bright and more salient areas in the field of vision. Statistical analyses found a stronger positive correlation in saliency than in relative luminance and at night-time rather than under daylight. The correlation found between relative luminance/saliency and fixation distribution suggests that relative luminance/saliency may attract the visual attention of pedestrians. It will be beneficial for practical applications via a better visual environment, including lighting and guiding facilities for pedestrians, especially at night.