Background Luminance Research Articles

24.2: Estimating the Perceptual Limits of Mobile Displays

AbstractThe quality of the displayed image in mobile devices is affected by the varying ambient illumination conditions. Determining appropriate viewing conditions for particular visual tasks requires appropriate instrumentation. However, visual tests can be more practical. We conducted experiments to explore the limitations of mobile displays in terms of the visibility of subtle targets. We explored the effect of background luminance and ambient lighting using two methodologies: a text detection task where the observer identifies characters embedded in noisy backgrounds and a threshold estimation staircase technique. We found that the text detection method holds promise as a surrogate for more complicated tests in the framework of a clinically practical implementation.

Computational Assessment of Text Legibility in Lecture Halls

Text presented in lecture halls often simultaneously appears on multiple visual displays (e.g., blackboards, projection screens, video monitors), which should be legible to the entire audience seated in an ideal viewing area. Existing guidelines identify this area as fan-shaped, but the origin of those guidelines and the data on which they are based are not specified. To supplement the guidelines, this paper describes the development of a computer program (available online) to compute locations in which all displays are legible to the audience, which considers the height, width, location and orientation of each display, text geometries (height, height-to-stroke width ratio) and its lighting conditions (background luminance, luminance contrast percent), as well as the observer’s visual acuity. This program was validated in a small experiment involving 21 subjects looking at text in a lecture hall, and further examined for two other test cases.

AVIAN VISION AND THE EVOLUTION OF EGG COLOR MIMICRY IN THE COMMON CUCKOO

Coevolutionary arms races are a potent force in evolution, and brood parasite-host dynamics provide classical examples. Different host-races of the common cuckoo, Cuculus canorus, lay eggs in the nests of other species, leaving all parental care to hosts. Cuckoo eggs often (but not always) appear to match remarkably the color and pattern of host eggs, thus reducing detection by hosts. However, most studies of egg mimicry focus on human assessments or reflectance spectra, which fail to account for avian vision. Here, we use discrimination and tetrachromatic color space modeling of bird vision to quantify egg background and spot color mimicry in the common cuckoo and 11 of its principal hosts, and we relate this to egg rejection by different hosts. Egg background color and luminance are strongly mimicked by most cuckoo host-races, and mimicry is better when hosts show strong rejection. We introduce a novel measure of color mimicry-"color overlap"-and show that cuckoo and host background colors increasingly overlap in avian color space as hosts exhibit stronger rejection. Finally, cuckoos with better background color mimicry also have better pattern mimicry. Our findings reveal new information about egg mimicry that would be impossible to derive by the human eye.

No-Reference JPEG image quality assessment based on Visual sensitivity

No-Reference JPEG image quality assessment based on Visual sensitivity

High-Resolution Multifocal Pupillographic Objective Perimetry in Glaucoma

The recent development of an objective and noninvasive perimetric technique using pupillary responses to sparse multifocal visual stimuli shows promise for the assessment of visual function in glaucoma. This study assesses the sensitivity and specificity of four variants of dichoptic multifocal pupillographic objective perimetry (mfPOP) with a high-resolution, 40-region/field stimulus. Nineteen normal subjects and 17 with open-angle glaucoma were tested with four 4-minute stimulus protocols, presented in eight segments of 30 seconds each. Achromatic multifocal stimuli comprised 40 test regions per eye arranged in a four-ring dartboard layout subtending 60° of visual field. Background luminance was 10 cd/m² with active stimulus regions displaying steady or flickered stimuli at 290 cd/m². Stimulus durations were between 33 and 150 ms, mean intervals between presentations to each test region ranged from 1 to 16 seconds. Fixation was monitored in real time. Longer mean intervals and durations resulted in better diagnostic performance. Best results were obtained with 150-ms flickered stimuli and a discriminant function that incorporated both amplitude and width of responses: ROC area under the curve 0.86 ± 0.05 (mean ± SE) across all visual field severities, (n = 34) and 1.00 ± 0.00 for moderate and severe fields (n = 10). mfPOP produces separate information on response delay and afferent and efferent defects at every point in the field. The diagnostic accuracy of the 40-region, 150-ms stimulus is comparable to that of commonly used subjective perimeters and encourages further investigation of this technique.

A Model of Luminance-Adaptation for Quantifying Brightness in Mixed Visual Adapting Conditions

The color appearance model gives us the proper brightness information and optimized display conditions for various viewing surroundings. However on conditions of low-level illumination or low background reflectivity, the performance of brightness estimation is relatively poor. Therefore, through our psychophysical experiments, we investigated the state of visual luminance adaptation for comparing single adaptations and mixed adaptations under a complex viewing field, and we also investigated background adaptation degrees and exponential nonlinearity factors for mixed adaptation models. It provides more accurate brightness predictions according to different adapting luminance, which is decided from object and background luminance.

Mapping Decadal Change in Anthropogenic Night Light

The Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) sensors have imaged emitted light from Earth's surface since the 1970's. Temporal overlap in the missions of 5 OLS sensors allows for intercalibration of the annual composites over the past 19 years [1]. The resulting image time series captures a spatiotemporal signature of human settlement growth and evolution. We use temporal Empirical Orthogonal Function (EOF) analysis to characterize and quantify patterns of temporal change in stable night light brightness and spatial extent since 1992. Temporal EOF analysis provides a statistical basis for representing spatially abundant temporal patterns in the image time series as uncorrelated vectors of brightness as a function of time from 1992 to 2009. The variance partition of the eigenvalue spectrum combined with temporal structure of the EOFs provides a basis for distinguishing between deterministic temporal trends and stochastic year to year variance. The low order EOFs and Principal Components (PC) space together discriminate both earlier (1990s) and later (2000s) increases and decreases in brightness. Inverse transformation of these low order dimensions reduces stochastic variance sufficiently so that tri-temporal composites depict deterministic decadal trends. The most pronounced changes occur in Asia. Throughout Asia a variety of different patterns of brightness increase are visible in tri-temporal brightness composites – as well as some conspicuous areas of apparently decreasing background luminance and, in many places, intermittent light suggesting development of infrastructure rather than persistently lighted development. Vicarious validation using higher resolution imagery reveals multiple phases of urban growth in several cities, numerous instances of highway construction, extensive terracing networks and hydroelectric dam construction [3]. Lights also allow us to quantify the size distribution and connectedness of different intensities of development. Over a wide range of brightnesses, size distributions of spatially contiguous lighted area are well-fit by power laws with exponents near -1 as predicted by Zipf's Law. However, the larger lighted segments are much larger than individual cities; they correspond to vast spatial networks of contiguous development.[2]

Closing the mind's eye: incoming luminance signals disrupt visual imagery.

Mental imagery has been associated with many cognitive functions, both high and low-level. Despite recent scientific advances, the contextual and environmental conditions that most affect the mechanisms of visual imagery remain unclear. It has been previously shown that the greater the level of background luminance the weaker the effect of imagery on subsequent perception. However, in these experiments it was unclear whether the luminance was affecting imagery generation or storage of a memory trace. Here, we report that background luminance can attenuate both mental imagery generation and imagery storage during an unrelated cognitive task. However, imagery generation was more sensitive to the degree of luminance. In addition, we show that these findings were not due to differential dark adaptation. These results suggest that afferent visual signals can interfere with both the formation and priming-memory effects associated with visual imagery. It follows that background luminance may be a valuable tool for investigating imagery and its role in various cognitive and sensory processes.

Measuring the meter: on the constancy of lightness scales seen against different backgrounds

The constancy of a 16-step achromatic Munsell scale was tested with regards to background variations in two experiments. In experiment 1 three groups of observers were asked to find lightness matches for targets in simultaneous lightness displays by using a 16-step achromatic Munsell scale placed on a white, black, or white-black checkered background. In experiment 2, a yellow-blue checkered background and a green-red checkered background replaced Munsell scales on the black and on the white backgrounds. Significant effects of scale background on matches were found only in experiment 1, suggesting that background luminance is a crucial factor in the overall appearance of the scale. The lack of significant differences in experiment 2, however, may stand for an overall robustness of the scale with respect to background luminance changes occurring within certain luminance ranges.

P1-1 Statistical analysis of VEPs to transient full-field pattern-reversal stimulation in 167 normal adults

Objective: To study the effect of age, gender, head size on patternreversal VEP. Method: Studies were conducted on 167 healthy adult volunteers (96 women, 71 men). The entire stimulating field subtended an angle of 16 degrees; each individual square of the checkerboard subtended 15, 30, or 60 minutes of arc measured to the eye. The subject was seated on a chair 127 cm from TV screen. Screen luminance was 25 luxes; background luminance was 15 luxes. VEPs were obtained by a stimulation frequency of a pattern reversal every 1 sec. Each evoked potential was the result of the summation of 60 responses. Midoccipital electrode was placed 5 cm above the inion, and was referred to a midfrontal reference electrode 12 cm above the nasion. We measured each peak latency of P50, N75, P100, and N145, and peak-to-peak amplitude of P50-N75, N75-P100, and P100-N145. Three way ANOVA was used to evaluate the effects of age, gender, head size on pattern-reversal VEP latency and amplitudes. Result: The age influenced each peaks latency. The checksize influenced each peak latency and amplitude (P50-N75, N75-P100). The smaller the checksize was, the larger both the latency and amplitude were. The gender each peak latency and each peak-to-peak amplitude. Latency was shorter and amplitude was larger in women than in men. The head size did not influence VEPs. Conclusion: Pattern VEP latencies are influenced by age, gender, and checksize. Pattern VEP amplitudes are influenced by gender and checksize. are influenced by gender and checksize.

Colour detection thresholds as a function of chromatic adaptation and light level

Colour threshold discrimination ellipses were measured for a number of states of chromatic adaptation and a range of luminance levels using the Colour Assessment and Diagnosis (CAD) test. An analysis of these results was carried out by examining the cone excitation signals along the cardinal axes that correspond to detection thresholds in the +L-M (reddish), -L+M (greenish), +S (bluish) and -S (yellowish) colour directions. The results reveal a strong linear relationship between the excitations induced by the adapting background field in each cone class and the corresponding changes needed for threshold detection. These findings suggest that the cone excitation change for threshold detection of colour signals is always the same for a given background excitation level (in any cone class), independent of the excitations generated in the other cone classes. These observations have been used to develop a model to predict colour detection thresholds for any specified background luminance and chromaticity within the range of values investigated in this study (e.g., luminances in the range 0.3 to 31 cd.m(-2) and chromaticities within the gamut of typical CRT displays). Predicted colour thresholds were found to be in close agreement with measured values with errors that do not, in general, exceed the measured within-subject variability.

Assessing Tooth Color Differences in Digital Facial Portraits

Although a large body of scientific literature shows that background color and luminance affect color perception, previous measurements of tooth color difference thresholds have not taken the effects of viewing context into account. The present study tested the hypothesis that differences in skin/gingival color influence individuals’ judgments of tooth color differences. Perceptibility and acceptability thresholds were determined in 10 individuals using a signal detection paradigm. They evaluated 500 pseudo-random presentations of two facial portraits: an African-American and a Caucasian. These portraits varied trial-to-trial only in the direction (CIELAB +L*, +a*, or +b*) or magnitude of the color difference between a portrait’s two central incisors. The individuals were significantly less sensitive to tooth color differences in the +L* direction in the Caucasian portrait than for any other combination of color direction or portrait type. Furthermore, comparable perceptibility and acceptability thresholds were generally not statistically significant from each other.

Assessing the impact of non-dilating the eye on full-field electroretinogram and standard flash response

We investigated the possibility of performing electroretinography (ERG) in non-pharmacologically dilated eyes using brighter flash (time-integrated) luminance. Photopic (N=26; background 25.5cd·m(-2), white LED flashes) and scotopic ERG (N=23, green LED flashes) luminance response functions were obtained simultaneously in a dilated (DE) and non-dilated eye (NDE). In the NDE, photopic V (max) b-wave amplitude was reduced by 14% (P<0.0001), implicit time prolonged (P<0.0001), and retinal sensitivity (log K) decreased by 0.38 log units (P<0.0001) with no effect on a-wave. Using a xenon strobe light (N=6) to increase flash luminance, V (max) remained lower by about 12% in the NDE (P=0.02). V (max) with LED and xenon was achieved at 3.9±1.0cd·s·m(-2) and 3.3±0.81cd·s·m(-2) in the DE and 10.6±1.2cd·s·m(-2) and 12.3±1.90cd·s·m(-2) in the NDE, that is an increase of 0.43 and 0.57 log unit (P<0.0001), respectively. Increasing background luminance by 0.50 log units (80cd·m(-2), N=4) resulted in implicit time normalization but not V (max) amplitude. Rod V (max) was decreased by 7% in NDE (P<0.05) and sensitivity reduced by 0.40 log units (P<0.0001), but our data suggest that the luminance may have not been sufficient to reach V (max) in all participants in the NDE and that the sensitivity change may have been due to an inadequate inter-stimulus interval. For the photopic ERG, increasing flash luminance is not sufficient to compensate for the smaller pupil size, whereas for the scotopic ERG, more data are needed to establish proper inter-stimulus interval to perform recordings in a non-pharmacologically dilated.

Photometric measurements for visibility level computations

Visibility level is a standard quality index in road lighting design. Three photometric values are needed to compute the visibility level of a target: its luminance, the luminance of its near background and the adaptation luminance. We discuss the consequences of how these parameters are set on the ability to predict the performance of a driver at target detection. An experiment was designed using a closed-road circuit. Sixteen targets were presented twice to 34 subjects. Six visibility level assessment methods were compared. The background luminance was set as the luminance at the bottom of the target, as the mean luminance around the target, or as the luminance associated with the maximum target contrast. The adaptation luminance was set either to the background luminance or to the mean luminance. The best non-linear fit between computed visibility level and target detection performance was found using the maximum contrast over the four sides of the square target, and setting the adaptation luminance to a unique estimated road luminance instead of the local background luminance. Even so, the variability of the visibility level data suggests great caution when using it as an index of road visibility.

Optic flow strongly affects brightness

It is well known that brightness/lightness is determined by the pattern of luminance within the target's context. Here we report a new phenomenon demonstrating that brightness is also strongly affected by the motion pattern within the context. We found that the optic flow of dots which is consistent with the dots moving in depth modulates their brightness. The brightness of light dots increases while the brightness of dark dots decreases by 30% when the dots appear to move away to twice the original distance from the viewer. The effect reverses when the dots appear to move nearer. The effect persists for a wide range of dot contrasts, velocities, sizes, densities, and background luminances. We also found that the density of dots modulates their brightness in a similar fashion, but the density effect alone is about 3 times weaker than that produced by the optic flow. To explain the phenomenon we suggest that the brain calculates brightness based on the estimated distance to the dots. When the distance appears to increase while the luminance of the dots remains constant, the brain interprets this as an increase in the dots' luminosity and (partially) displays this increased luminosity as the increased brightness. This interpretation is corroborated by the fact that the size of the dots appears to be modulated in the same fashion as their brightness: the receding dots seem to grow, while the approaching dots seem to shrink.

Effects of color and background luminance on minimal legible size of dynamic Chinese characters presented on a LCD monitor for low‐vision and normally sighted users

Abstract— The effects of velocity (3, 5, and 7 cm/sec), stimulus color (red, green, and blue), and background luminance (20–80% white, in increments of 15%) on minimal legible size of dynamic Chinese characters, were examined. Participants were divided into low‐vision, severely myopic, and normal‐vision groups. They were asked to recognize the stimulus Chinese characters, which were presented with varying velocity on a screen. Analysis showed that the minimal legible size was significantly greater for those in the low‐vision and severely myopic groups than for those in the normal‐vision group, and the minimal legible size for the low‐vision group was greater than that for the severely myopic group. The minimal legible size was significantly greater when the stimuli were green than when they were red or blue; however, no significant difference was found between green and blue stimuli or between blue and red ones. An effect was observed for background luminance: a higher ratio of white in the gray background yielded a smaller minimal legible size than did a lower ratio of white. Additionally, velocity significantly affected the minimal legible size: a velocity of 3 cm/sec resulted in lower minimal legible size than did a velocity of 7 cm/sec. Results have implications for electronic text information design or icon design for visually impaired individuals.

42.2: Using the Selective‐Reset to Achieve a “Real Black” with 50‐in. Full HD PDPs

Abstract“Real black” plasma display panels (PDPs) having a background luminance of zero cd/m2 must be realized to obtain high picture quality. PDPs, however, must have reset discharges to initialize cell conditions, regardless of expressing any of the gray levels. The light emission from the reset discharges becomes a background luminance, degrading the picture quality having low luminance levels. A technique of substituting the role of the reset discharges is proposed for 50‐in. full‐HD PDPs. with this technique an infinite dark‐room contrast ratio is obtained. However, it has the problem of the discharge delay. A solution to this was proposed by using the frame reset or the minimum surface reset discharge and selective reset.

P‐95: Driving Waveform to Reduce Power Consumption in AC‐PDP with MgO Single‐Crystal Powder

AbstractThe negative falling voltage during the reset‐period affects the power consumption as well as the statistical delay time during the subsequent address period. In the PDP without MgO single‐crystal powder, the negative falling reset voltage should be increased in the negative direction to minimize the statistical delay time, whereas in the PDP with MgO single‐crystal powder, the negative falling reset voltage can be adjusted to minimize the power consumption thanks to the improvement of the statistical delay characteristics. As a result of adjusting the negative falling voltage in the 50‐inch FHD PDP with MgO single‐crystal powder, the consumed power and background luminance decreased about by 8.1 % and 33 % for the full black pattern, respectively. for the full‐white pattern, the consumed power was reduced about by 5.6 % and the luminous efficiency was improved about by 3.5 %.

Cortical contributions to saccadic suppression

The stability of visual perception is partly maintained by saccadic suppression: the selective reduction of visual sensitivity that accompanies rapid eye movements. The neural mechanisms responsible for this reduced perisaccadic visibility remain unknown, but the Lateral Geniculate Nucleus (LGN) has been proposed as a likely site. Our data show, however, that the saccadic suppression of a target flashed in the right visual hemifield increased with an increase in background luminance in the left visual hemifield. Because each LGN only receives retinal input from a single hemifield, this hemifield interaction cannot be explained solely on the basis of neural mechanisms operating in the LGN. Instead, this suggests that saccadic suppression must involve processing in higher level cortical areas that have access to a considerable part of the ipsilateral hemifield.

A contrast polarity search effect in letter identification

Lauren Scharff lauren.scharff@usafa.edu Albert Ahumada al.ahumada@nasa.gov) U. S. Air Force Academy Introduction Scharff and Ahumada (2002, 2003abc) measured text legibility for light text and dark text. For paragraph scanning and letter identification, performance was better for dark text than light text when we equate Weber contrast (the difference between text and background luminance divided by the background luminance). In recent studies with better stimulus control (Scharff & Ahumada, 2005; 2008), we continued to find a small, but consistent benefit of dark text for letter identification. Reading involves both scanning and identification. In the experiments below we replicate our scanning result with our improved apparatus and add scanning to our letter identification task by manipulating eccentricity.