Visibility Threshold Research Articles

Stroboscopic effect: contrast threshold function and dependence on illumination level.

The stroboscopic visibility measure (SVM) is a method used to quantify the stroboscopic effect visibility in general illumination application. SVM has been defined previously based on a limited number of frequencies and participants. To validate and extend SVM, five perception experiments are presented, measuring the visibility threshold of light waveforms modulated at several frequencies, conducted in two different labs. A power function is fitted through the aggregated results to develop a stroboscopic effect contrast threshold function for a "standard observer," which can be used to normalize SVM. An additional experiment shows the dependency on illumination level, extending the validity of SVM to other applications.

Resolution: Digital materialities, thresholds of visibility

Resolution: Digital materialities, thresholds of visibility

Perceptual Enhancement of Low Light Images Based on Two-Step Noise Suppression

Low-light images are seriously corrupted by noise due to the low signal-to-noise ratio. In low intensity, just-noticeable-difference (JND) is high, and thus the noise is not perceived well by human eyes. However, after contrast enhancement, the noise becomes obvious and severe, because JND decreases as intensity increases. Thus, contrast enhancement without considering human visual perception causes serious noise amplification in low-light images. In this paper, we propose perceptual enhancement of low-light images based on two-step noise suppression. We adopt two-step noise suppression based on noise characteristics corresponding to human visual perception. First, we perform noise aware contrast enhancement using a noise-level function. However, the increase of the intensity caused by contrast enhancement reduces JND in low intensity, which makes noise much more visible by human eyes. Second, we perceptually reduce noise in images while preserving details using a JND model, which represents noise visibility in contrast enhancement. We estimate the noise visibility based on the intensity change using luminance adaptation. Also, we extract image details by contrast masking and visual regularity, because textural regions have higher visibility thresholds than the smooth ones. Based on the human visual characteristics, we perform perceptual noise suppression using the JND model. Experimental results show that the proposed method perceptually enhances contrast in low-light images while successfully minimizing distortions and preserving details.

An analytical model for the response of carbon/epoxy-aluminum honeycomb core sandwich structures under quasi-static indentation loading

An analytical model is developed to predict the loading and unloading response, as well as the residual dent diameter and dent depth, of carbon/epoxy-aluminum honeycomb core composite sandwich structures undergoing quasi-static indentation loading. The model considers damage created using spherical indenters and is valid up to the barely visible external damage threshold. The initial low load regime (until the onset of core crushing) is modeled using a combination of local Hertzian indentation of an elastic half-space and small deflection plate theory of a circular plate on an elastic foundation. For loads above those required to cause core crushing, the model uses the Rayleigh-Ritz method of energy minimization with the total system energy determined using a combination of face sheet bending energy, face sheet membrane energy and work done to the core during both elastic deformation and crushing. Degraded face sheet properties are used in the model beyond the onset of face sheet delamination, which is predicted using Griffith’s energy criterion. The model is validated using experimental results for sandwich structures consisting of quasi-isotropic 8- (thin) and 16- (thick) ply carbon/epoxy face sheets and aluminum honeycomb cores. The results show that the overall mechanics of the model are fundamentally correct and reflective of physical behavior. Thus, in its present form the model shows promise as a preliminary design tool.

Emergency Cinema and the Dignified Image: Cell Phone Activism and Filmmaking in Syria

While the proliferation of digital technology has expanded the capacity to document human rights violations and publicize them via cell phone, cloud, and social networks, raw footage of state-sponsored violence is often the subject of competing interpretations that multiply through their viral circulation. Accordingly, much recent attention has been placed on the evidentiary uncertainty that attends digital documents coming out of Syria. This article offers an alternative framework through which to think about the efficacy of images that circulate outside of state institutions and corporate media outlets. Focusing on works by Rabih Mroué, Ossama Mohammed, and the filmmaking collective Abounaddara, this article examines how the videos produced during the Syrian uprisings and war give rise to a critical reflection on cinematic truth and the medium's long-standing correlation with violence and death. The affective force of images that operate at the threshold of visibility unsettles the terms of both human rights practice and documentary filmmaking.

Experimental Observations of the Visibility Threshold of Illusory effects in Hermann Grid, Sinusoidal and Square Gratings and their Possible Implications

Experimental Observations of the Visibility Threshold of Illusory effects in Hermann Grid, Sinusoidal and Square Gratings and their Possible Implications

The approximate entropy concept extended to three dimensions for calibrated, single parameter structural complexity interrogation of volumetric images

Reconstructive volumetric imaging permeates medical practice because of its apparently clear depiction of anatomy. However, the tell tale signs of abnormality and its delineation for treatment demand experts work at the threshold of visibility for hints of structure. Hitherto, a suitable assistive metric that chimes with clinical experience has been absent. This paper develops the complexity measure approximate entropy (ApEn) from its 1D physiological origin into a three-dimensional (3D) algorithm to fill this gap. The first 3D algorithm for this is presented in detail. Validation results for known test arrays are followed by a comparison of fan-beam and cone-beam x-ray computed tomography image volumes used in image guided radiotherapy for cancer. Results show the structural detail down to individual voxel level, the strength of which is calibrated by the ApEn process itself. The potential for application in machine assisted manual interaction and automated image processing and interrogation, including radiomics associated with predictive outcome modeling, is discussed.

Estimating just‐noticeable distortion for images/videos in pixel domain

Existing pixel-based just noticeable distortion (JND) models only take into account luminance adaptation and texture masking (TM). Similarly, existing discrete cosine transform (DCT) based models do not take into account foveal vision effects and do not estimate TM efficiently. As human visual system (HVS) is not sensitive to distortion below the JND threshold, estimation of the perceptual visibility threshold is widely used in digital and video processing applications. The authors propose a comprehensive and efficient pixel-based JND model incorporating all major factors which contribute to the JND estimation. The evaluation of contrast masking (CM) is done by distinguishing the edge and TM with respect to the entropy masking properties of the HVS. Similarly, the foveal vision effects are also taken into account for the comprehensive estimation of contrast sensitivity function (CSF). Hence, the proposed pixel-based JND model incorporates the spatio-temporal CSF, foveal vision effects, influence of eye-movement, luminance adaptation and CM to be more consistent with human perception. The incorporation of these important factors makes the proposed model the most comprehensive and efficient in the current literature. Psychophysical experiments were performed to test the proposed model. The results show the proposed model comprehensively outperforms other existing models proving its efficiency.

P‐141: Phantom Array Effect of LED Lighting

This paper studies the influence of the LED modulation frequency and eye saccade amplitude on the visibility of the phantom array effect. Results show that the phantom array effect becomes invisible at 3000 Hz. Besides, visibility thresholds at lower frequencies were not influenced by saccade amplitudes (20° and 40°).

Neural evidence for the subliminal processing of facial trustworthiness in infancy

Face evaluation is thought to play a vital role in human social interactions. One prominent aspect is the evaluation of facial signs of trustworthiness, which has been shown to occur reliably, rapidly, and without conscious awareness in adults. Recent developmental work indicates that the sensitivity to facial trustworthiness has early ontogenetic origins as it can already be observed in infancy. However, it is unclear whether infants’ sensitivity to facial signs of trustworthiness relies upon conscious processing of a face or, similar to adults, occurs also in response to subliminal faces. To investigate this question, we conducted an event-related brain potential (ERP) study, in which we presented 7-month-old infants with faces varying in trustworthiness. Facial stimuli were presented subliminally (below infants’ face visibility threshold) for only 50ms and then masked by presenting a scrambled face image. Our data revealed that infants’ ERP responses to subliminally presented faces differed as a function of trustworthiness. Specifically, untrustworthy faces elicited an enhanced negative slow wave (800–1000ms) at frontal and central electrodes. The current findings critically extend prior work by showing that, similar to adults, infants’ neural detection of facial signs of trustworthiness occurs also in response to subliminal face. This supports the view that detecting facial trustworthiness is an early developing and automatic process in humans.

Color breakup visibility thresholds for 2‐field sequential colors

AbstractNowadays local primary desaturation has been proved to be an effective method to suppress the color breakup for field‐sequential‐color (FSC) displays. However, little attention has been focused on the interaction between various subfield colors and the color breakup visibility. In this article, a perception experiment was conducted with the help of a 120 Hz 2‐field FSC display to investigate the thresholds of color breakup visibility along different hue directions with a constant white point in the standard color space. The experimental results show that the color breakup visibility is various when using different subfield colors for temporal combination. A relative high threshold value or low sensitivity of color breakup visibility can be observed when subfield colors are chosen along the blue‐yellow direction while becoming perceptible easily along magenta‐cyan direction. The results and analysis of our experiments are promising to optimize the performance of local primary desaturation. Meanwhile, other applications using the temporal color fusion such as tunable lighting can also benefit from the conclusion of our work to suppress the color breakup effect.

Field Test Results of Layered Division Multiplexing for the Next Generation DTV System

In this paper, we present field test results of a layered division multiplexing (LDM) technology for the next generation digital television system, and analyze the results in several scenarios such as rooftop, indoor, and mobile receptions. In order to evaluate performance of the LDM technology, the field strength or the reception power is measured for all considered scenarios. Furthermore, the threshold of visibility, the marginal reception power, and the erroneous second ratio are measured for fixed, indoor, and mobile receptions, respectively. The field test results show that LDM technology enables broadcaster not only to efficiently provide a variety of services (e.g., mobile, indoor, and stationary services) with different robustness within a single radio frequency (RF) channel but also to increase flexible usage of the RF channel.

Can a Word Sound Like a Shape Before You Have Seen It? Sound-Shape Mapping Prior to Conscious Awareness

Nonarbitrary mappings between sound and shape (i.e., the bouba-kiki effect) have been shown across different cultures and early in development; however, the level of processing at which this effect arises remains unclear. Here we show that the mapping occurs prior to conscious awareness of the visual stimuli. Under continuous flash suppression, congruent stimuli (e.g., “kiki” inside an angular shape) broke through to conscious awareness faster than incongruent stimuli. This was true even when we trained people to pair unfamiliar letters with auditory word forms, a result showing that the effect was driven by the phonology, not the visual features, of the letters. Furthermore, visibility thresholds of the shapes decreased when they were preceded by a congruent auditory word form in a masking paradigm. Taken together, our results suggest that sound-shape mapping can occur automatically prior to conscious awareness of visual shapes, and that sensory congruence facilitates conscious awareness of a stimulus being present.

Experimental investigation of the effect of binocular disparity on the visibility threshold of asymmetric noise in stereoscopic viewing.

Stereoscopic images could have asymmetric distortions caused by image processing in capture, synthesis, and compression of them. In 3D perception in stereoscopic display, the visibility threshold of the asymmetric distortions in the left and right images is important, which is tolerable to the human visual system. In this paper, we investigate the effect of the binocular disparity on the visibility threshold of asymmetric noises in stereoscopic images via subjective assessments. Existing just-noticeable-difference (JND) models for stereoscopic images have not taken into account the effect of the disparity in stereoscopic viewing. In this paper, we subjectively assessed the visibility threshold of asymmetric noises in stereoscopic images according to the disparity. Subjective evaluations showed that large disparity magnitudes could make more tolerable to perceive the asymmetric noises in the stereoscopic viewing.

HEVC over DVB-T2 기반 지상파 4K-UHDTV 방송을 위한 양시청 기준값 실험실 테스트 결과

본 연구에서는 HEVC로 인코딩된 스트림을 6MHz 대역폭 DVB-T2 시스템을 통해서 전송하는 우리나라 지상파 4K-UHD 실험방송 환경에서, 상용 수신기 3종에 대해서 양시청 최소 신호 대 잡음비(ToV C/N)와 양시청 수신기 최소 입력 전계 레벨(Sensitivity)을 실험실 테스트를 통해서 측정하였다. 26.37Mbps 전송률을 기준으로, ToV 평균 C/N=18.8dB 정도로 측정되었고, 수신기 Sensitivity는 최소 -84.2dBm에서 최대 -80.0dBm으로 측정되었다. 이로부터, 수신기 노이즈 바닥(Floor)은 평균 -100dBm 가량으로 계산되었다. In this study, HEVC over DVB-T2 systems with a bandwidth of 6 MHz is considered, particularly for the terrestrial 4K-UHDTV broadcasting service in the Republic of Korea. The threshold of visibility carrier-to-noise power ratio (ToV C/N) and the receiver minimum required input level (sensitivity) for satisfying the subjective picture failure (SPF) condition are measured in the laboratory. It is observed, for transmitting 26.37 Mbps data stream correctly, that ToV C/N is 18.8 dB on average, and the receiver sensitivity is varied from minimum -84.2 dBm to maximum -80.0 dBm. Based on the results, the receiver noise floor is calculated by -100 dBm on average.

Skin conductance reveals the early development of the unconscious processing of emotions

The ability to rapidly distinguish between positive and negative facial expressions of emotions is critical for adaptive social behaviour. Increasing evidence has shown that emotions can be processed even at an unconscious level in adults. Yet, very little is still known about the early ontogeny of the unconscious processing of emotional signals conveyed by faces. Here, we investigated the processing of subliminally presented face emotional stimuli in infants as young as 3–4 months of age and sought to clarify its neural underpinnings by exploring the role of the autonomic nervous system. Using a visual preference paradigm, Experiment 1 determined the visibility threshold for happy and angry faces and established that infants detected both happy and angry faces at 200- but not at 100 msec. By measuring skin conductance response (SCR), Experiment 2 showed that the autonomic nervous system of infants reacted to both subliminally (100 msec) and supraliminally (200 msec) presented face expressions of emotions, and that SCR were higher for angry than happy facial expressions. Results revealed that 3–4 month-old infants respond to positive and negative emotions even at an unconscious level, but also show that angry faces possess an intrinsic alerting characteristics, suggestive of an adaptive meaning of the physiological response. Findings are discussed in terms of subcortical learning of emotions, and the possibility that the amygdala may be involved in such process.

Direct assimilation of Chinese FY-3C Microwave Temperature Sounder-2 radiances in the global GRAPES system

Abstract. FengYun-3C (FY-3C) is an operational polar-orbiting satellite carrying the new-generation microwave sounding instruments in China. This paper describes the assimilation of the FY-3C Microwave Temperature Sounder-2 (MWTS-2) radiances in the Global and Regional Assimilation and PrEdiction System (GRAPES) of China Meteorological Administration. A quality control (QC) procedure for the assimilation of MWTS-2 radiance is proposed. Extensive monitoring before assimilation shows that MWTS-2 observations exhibit a clear striping pattern. A technique combining principal component analysis (PCA) and ensemble empirical mode decomposition (EEMD) is applied to the observations to remove the striping noise. Cloudy field-of-views (FOVs) are identified by applying the Visible and InfrarRed Radiometer (VIRR) cloud fraction threshold of 76 %. Other QC steps are conducted in the follow order: (i) coastal FOVs are removed, (ii) eight outmost FOVs are not used, (iii) channel 5 data over sea ice and land are not used, (iv) channel 6 observations are not used if the terrain altitudes are higher than 500 m, and (v) outliers with large differences between observations and model simulations are removed. Approximately 83, 75, 40, and 40 % of the observations are removed by the proposed QC for channels 5–8, respectively. After QC, the global biases and standard deviations are reduced significantly. The assimilation of the MWTS-2 radiances shows a positive impact when the control experiment assimilates only conventional observations. The experiments also show that the analysis and forecast errors are slightly reduced when the striping noise is removed from the observations. The quality control scheme of extracting the striping noise may contribute to the analysis and forecast accuracy. The impact of MWTS-2 is neutral when the conventional data and other satellite data are all assimilated.

Surface manifestation of internal waves emitted by submerged localized stratified turbulence

The internal waves (IWs) radiated by the turbulent wake of a sphere of diameter $D$ towed at speed $U$ are investigated using three-dimensional fully nonlinear simulations performed in a linearly stratified Boussinesq fluid with buoyancy frequency $N$. The study focuses on a broad range of wave characteristics in the far field of the turbulent wave source, specifically at the sea surface (as modelled by a free-slip rigid lid) where the IWs reflect. Six simulations are performed at Reynolds number $Re\equiv UD/{\it\nu}\in \{5\times 10^{3},10^{5}\}$ and Froude number $Fr\equiv 2U/(ND)\in \{4,16,64\}$, where ${\it\nu}$ is viscosity. The wave-emitting wake is located at a fixed distance of $9D$ below the surface. As the wake evolves for up to $O(300)$ units of buoyancy time scale $1/N$, IW characteristics, such as horizontal wavelength ${\it\lambda}_{H}$ and wave period $T$, are sampled at the sea surface via wavelet transforms of horizontal divergence signals. The statistics of amplitudes and orientations of IW-induced surface strains are also reported. The mean dimensionless observable wavelength $\overline{{\it\lambda}}_{H}/D$ at the sea surface decays in time as $(Nt)^{-1}$, which is due to the waves’ dispersion. This observation is in agreement with a linear propagation model that is independent of the wake $Re$ and $Fr$. This agreement further suggests that the most energetic waves impacting the surface originate from the early-time wake that is adjusting to buoyancy. The most energetic dimensionless wavelength $\hat{{\it\lambda}}_{H}/D$ is found to scale as $Fr^{1/3}$ and decrease with $Re$, which causes the arrival time (in $Nt$ units) of the strongest waves at the surface to scale as $Fr^{-1/3}$ and increase with $Re$. This wavelength $\hat{{\it\lambda}}_{H}$ is also found to correlate with the vertical Taylor scale of the wake turbulence. IW-driven phenomena at the surface that are of interest to an observer, such as the local enrichment of surfactant and the transport of ocean surface tracers, are also examined. The local enrichment ratio of surface scalar scales linearly with the steepness of IWs that reach the surface, and the ratio often exceeds a possible visibility threshold. The Lagrangian drifts of ocean tracers, which are linked to the nonlinear interaction between incident and reflecting IW packets, create a local divergence in lateral mass transport right above the wake centreline, an effect that intensifies strongly with increasing $Fr$. The findings of this study may serve as a platform to investigate the generation and surface manifestation of IWs radiated by other canonical submerged stratified turbulent flows.

Comparison of Visibility Threshold on Different Chromatic Contrast Objects

The aim of this study was to compare the visibility threshold of eight plates with different chromatic contrast. The staircase psychophysics method based on the resolution of gaps in Landolt C was used to determine the average visibility threshold. Thirty young adults with best-corrected visual acuity of 6/6, normal colour perception and no history of ocular diseases were recruited. The results showed a combination of white on blue background plate gave a highest visibility level (mean=44.48±6.37m), while red on a blue background was the least visible combination (mean=33.30±4.68m). In conclusion, the chromatic contrast of an object can affect the visibility threshold.
 Keywords: chromatic contrast, visibility threshold

Comparison of Terrestrial DTV Systems: ISDB-TB and DVB-T2 in 6 MHz

The present paper completely discusses the ISDB-TB and the DVB-T2 systems. There are demonstrated the differences and similarities since BTS data entrance to ISDB-TB as well T2-MI to DVB-T2, up to base band generation. Tests for both broadcast television systems have been performed using 6 MHz of bandwidth. The tests procedure in laboratory used TOV (Threshold of Visibility) criteria under different transmission's parameters to ISDB-TB and DVB-T2. It was analyzed the TV interferences as sensibility performance, C/N threshold, Impulsive Noise and Multipath.