A large-scale real-life crowd steering experiment via arrow-like stimuli

We introduce "Moving Light": an unprecedented real-life crowd steering experiment that involved about 140.000 participants among the visitors of the Glow 2017 Light Festival (Eindhoven, NL). Moving Light targets one outstanding question of paramount societal and technological importance: "can we seamlessly and systematically influence routing decisions in pedestrian crowds?" Establishing effective crowd steering methods is extremely relevant in the context of crowd management, e.g. when it comes to keeping floor usage within safety limits (e.g. during public events with high attendance) or at designated comfort levels (e.g. in leisure areas). In the Moving Light setup, visitors walking in a corridor face a choice between two symmetric exits defined by a large central obstacle. Stimuli, such as arrows, alternate at random and perturb the symmetry of the environment to bias choices. While visitors move in the experiment, they are tracked with high space and time resolution, such that the efficiency of each stimulus at steering individual routing decisions can be accurately evaluated a posteriori. In this contribution, we first describe the measurement concept in the Moving Light experiment and then we investigate quantitatively the steering capability of arrow indications.Comment: 8 page

A large-scale real-life crowd steering experiment via arrow-like stimuli

We introduce “Moving Light”: an unprecedented real-life crowd steering experiment that involved about 140.000 participants among the visitors of the Glow 2017 Light Festival (Eindhoven, NL). Moving Light targets one outstanding question of paramount societal and technological importance: “can we seamlessly and systematically influence routing decisions in pedestrian crowds?” Establishing effective crowd steering methods is extremely relevant in the context of crowd management, e.g. when it comes to keeping floor usage within safety limits (e.g. during public events with high attendance) or at designated comfort levels (e.g. in leisure areas). In the Moving Light setup, visitors walking in a corridor face a choice between two symmetric exits defined by a large central obstacle. Stimuli, such as arrows, alternate at random and perturb the symmetry of the environment to bias choices. While visitors move in the experiment, they are tracked with high space and time resolution, such that the efficiency of each stimulus at steering individual routing decisions can be accurately evaluated a posteriori. In this contribution, we first describe the measurement concept in the Moving Light experiment and then we investigate quantitatively the steering capability of arrow indications

Preferred color gamut boundaries for wide-gamut and multiprimary displays

\u3cp\u3ePreferred chroma enhancement and its dependence on hue are studied in a two-part experiment using a wide-gamut multiprimary display. Earlier research showed a clear dependence on hue but was limited by the gamut of the display it employed; the present work builds on this while easing the gamut constraints. In the first part of the present experiment, a tuning task was used to refine the preference for chroma boost starting with standard-gamut (Rec. 709) images. The overall median preferred boost is roughly 20%, but it is not uniform over hues: the preferred boost for orange, yellow, green, and cyan colors is greater than that for blue, magenta, and red colors. Dependence on image content and observer is noted, though a content-independent chroma boost created by aggregating preference over many images performs well. An adjustment parameter for overall chroma, which incorporates the hue dependence averaged over image content, should be sufficient to handle the vast majority of interobserver variance in preference. In the second part of the experiment, various chroma boost algorithms were evaluated through a paired comparison task. The prescribed hue-dependent chroma boost is preferred over all other variations, and all hue-preserving chroma boost variations are preferred over both colorimetrically accurate and nabox drawings light down and lefẗve same-drive-signal renderings. The results may be applied in display design to select gamut boundaries that maximize satisfaction over the observer population. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 169-178, 2014\u3c/p\u3

Invited paper: modeling the visibility of temporal light artifacts

This paper describes temporal light artifacts with a focus on flicker and presents the state of the art of quantifying the visibility of these artifacts. The results of new experiments are compared against previous measures of display flicker

Spatio-chromatic sensitivity explained by post-receptoral contrast

We measured and modeled visibility thresholds of spatial chromatic sine-wave gratings at isoluminance. In two experiments we manipulated the base color, direction of chromatic modulation, spatial frequency, the number of cycles in the grating, and grating orientation. In Experiment 1 (18 participants) we studied four chromatic modulation directions around three base colors, for spatial frequencies 0.15-5 cycles/deg. Results show that the location, size and orientation of fitted ellipses through the observer-averaged thresholds varied with spatial frequency and base color. As expected, visibility threshold decreased with decreasing spatial frequency, except for the lowest spatial frequency, for which the number of cycles was only three. In Experiment 2 (27 participants) we investigated the effect of the number of cycles at spatial frequencies down to 0.025 cycles/deg. This showed that the threshold elevation at 0.15 cycles/deg in Experiment 1 was at least partly explained by the small number of cycles. We developed two types of chromatic detection models and fitted these to the threshold data. Both models incorporate probability summation across spatially weighted chromatic contrast signals, but differ in the stage at which the contrast signal is calculated. In one, chromatic contrast is determined at the cone receptor level, the dominant procedure in literature. In the other model, it is determined at a postreceptoral level, that is, after cone signals have been transformed into chromatic-opponent channels. We applied Akaike's Information Criterion to compare the performance of the models and calculated their relative probabilities and evidence ratios. We found evidence in favor of the second model and conclude that postreceptoral contrast is the most accurate determinant for chromatic contrast sensitivity

Spatio-chromatic sensitivity explained by post-receptoral contrast

We measured and modeled visibility thresholds of spatial chromatic sine-wave gratings at isoluminance. In two experiments we manipulated the base color, direction of chromatic modulation, spatial frequency, the number of cycles in the grating, and grating orientation. In Experiment 1 (18 participants) we studied four chromatic modulation directions around three base colors, for spatial frequencies 0.15-5 cycles/deg. Results show that the location, size and orientation of fitted ellipses through the observer-averaged thresholds varied with spatial frequency and base color. As expected, visibility threshold decreased with decreasing spatial frequency, except for the lowest spatial frequency, for which the number of cycles was only three. In Experiment 2 (27 participants) we investigated the effect of the number of cycles at spatial frequencies down to 0.025 cycles/deg. This showed that the threshold elevation at 0.15 cycles/deg in Experiment 1 was at least partly explained by the small number of cycles. We developed two types of chromatic detection models and fitted these to the threshold data. Both models incorporate probability summation across spatially weighted chromatic contrast signals, but differ in the stage at which the contrast signal is calculated. In one, chromatic contrast is determined at the cone receptor level, the dominant procedure in literature. In the other model, it is determined at a postreceptoral level, that is, after cone signals have been transformed into chromatic-opponent channels. We applied Akaike's Information Criterion to compare the performance of the models and calculated their relative probabilities and evidence ratios. We found evidence in favor of the second model and conclude that postreceptoral contrast is the most accurate determinant for chromatic contrast sensitivity

Quantifying the visibility of periodic flicker

\u3cp\u3eThree experiments that measure the visibility of periodic flicker are presented. Temporal light modulations were presented to a large visual field to make the results valid for general lighting applications. In addition, the experiments were designed to control for flicker adaptation. In the first experiment, the sensitivity of human observers to light modulations with a sinusoidal waveform at several temporal frequencies up to 80 Hz was measured. The results showed that the sensitivity to flicker (that is, the inverse of the Michelson contrast) is as high as 500 for frequencies between 10 and 20 Hz, which is more than twice the maximum sensitivity reported in the literature. In the second experiment, the sensitivity to flicker for light modulations with complex waveforms, composed of two or three frequency components, was measured. Sensitivity to flicker was found to be higher than the sum of the sensitivities of the individual frequency components of the complex waveform. Based on these results, we defined the flicker visibility measure (FVM), predicting flicker visibility by a weighted summation of the relative energy of the frequency components of the waveform. In the third experiment, sensitivity to realistic waveforms (that is, waveforms of light emitting diode [LED] light sources available on the market) was measured. The flicker predictions of FVM showed a high correlation with the experimental data, in contrast to some other existing flicker measures, including flicker index and percent flicker, demonstrating the usefulness of the measure to objectively assess the visibility of periodic flicker for lighting applications.\u3c/p\u3

Smoothness and flicker perception of temporal color transitions

\u3cp\u3eWe present results from two experiments designed to explore temporal properties of human color vision relevant to dynamic lighting applications. Sensitivity for smoothness perception of linear temporal transitions and flicker visibility was tested. Stimuli in the first experiment were linear color transitions, varying in either lightness, chroma or hue, around a base color represented in CIE LCh. Results show a significantly lower smoothness threshold for lightness changes than for chroma and hue changes. Moreover, the thresholds for lightness change show independence from the chroma and hue of the base color in contrast to thresholds for chroma and hue changes. A difference between the sensitivity for chroma and hue changes was also demonstrated. In the second experiment, the sensitivity for linear transitions is compared to flicker sensitivity for the same base colors. Results show that visibility thresholds for flicker are significantly lower than the thresholds smoothness of linear changes, demonstrating an influence of the type of change to the temporal sensitivity. The results from the flicker experiment show the same tendencies as the linear changes. The results from these experiments show a need for a model of perceived smoothness to control temporal changes in dynamic lighting systems and give the first steps towards building such a model.\u3c/p\u3

Preferred and maximally acceptable color gamut for reproducing natural image content

With the development of wide-gamut display technology, the need is clear for understanding the required size and shape of color gamut from the viewers' perspective. To that end, experiments were conducted to explore color-gamut requirements based on viewers' preferred level of chroma enhancement of standard-gamut images. Chroma preferences were measured for multiple hues using single-hue images, and a corresponding hue-dependent preferred chroma enhancement was successfully applied to natural, multi-hue images. The multi-hue images showed overall success, though viewers indicated that reds could be decreased even further in colorfulness, and yellows could be increased, which may argue in favor of multi-primary displays. Viewer preferences do vary within the population, primarily in overall chroma level, and the differences can be largely accounted for with a single parameter for chroma-level adjustment that includes the preferred hue dependence. Image content dependencies were also found, but they remain too complex to model. The huedependent chroma preference results can be applied to display design and color-enhancement algorithms. © Copyright 2010 Society for Information Display