Effect of glare on reaction time for peripheral vision at mesopic adaptation

When a bright light is present in the field of view, visibility is dramatically reduced. Many studies have investigated the effect of glare on visibility considering foveal vision. However, the effects on peripheral vision have received little attention. In a previous work [J. Opt. Soc. Am. A 25, 1790 (2008)], we showed that the effect of glare on reaction time (RT) for foveal vision at mesopic adaptation depends on the stimulus spatial frequency. In this work, we extend this study to peripheral vision. We measured the RT of achromatic sinusoidal gratings as a function of contrast for a range of spatial frequency, and eccentricity, and for two glare levels, in addition to the no-glare condition. Data were fitted with Piéron's law, following a linear relationship. We found that glare increases the slope of these lines for all conditions. These slopes seem to depend critically on eccentricity for 4 cycles/degree (c/deg), but not for 1 and 2 c/deg. We explain our results in terms of the contrast sensitivity (gain) of the underlying detection mechanisms.     

Single image veiling glare removal

Photographing against a bright light source is difficult since the direct light from the light source causes glare phenomenon in the lens, changing the colour balance and reducing the image contrast within the field of view. To address the effect, we introduce a glare formation model that accounts for the characters of the glare. Based on the model, we propose a single image processing method to remove the glare in the images by decomposing the image into the scene layer and the glare layer. We then adjust the brightness and the colour balance of the scene layer to eliminate the influences of the glare. In order to enhance the contrast decreased by the glare, we use a local standard deviation-based contrast enhancement algorithm to boost the details while avoiding excessive enhancement. Experimental results show that the method removes the majority of the glare and improves the local contrast effectively.     

Effect of glare on simple reaction time

We systematized the study of the effect of glare on reaction time (RT), for visual conditions similar to the ones found during night driving: Mesopic range of adaptation (0.14 cd/m2), glare levels of the order of those produced by car headlights (E(G)=15, 60 lx), suprathreshold luminance contrasts, and a variety of spatial frequencies covering the selected range of visibility (1, 2, 4, and 8 c/deg). We found that for the no-glare situation, RT increases with decreasing contrast and increasing spatial frequency, which agrees with previous findings. When data are plotted as a function of the inverse of contrast, RT varies linearly, with k--the RT-contrast factor of Pieron's law--representing the slope of the lines. The effect of glare on RT is an increase in the slope of these lines. This effect is different for each spatial frequency, which cannot be accounted for in the classic approach considering that glare can be replaced by a single veiling luminance. We show that the effect of glare on RT must be modeled by an equivalent glare luminance that depends on spatial frequency.     

3D shape measurement of objects with high dynamic range of surface reflectivity

This paper presents a method that allows a conventional dual-camera structured light system to directly acquire the three-dimensional shape of the whole surface of an object with high dynamic range of surface reflectivity. To reduce the degradation in area-based correlation caused by specular highlights and diffused darkness, we first disregard these highly specular and dark pixels. Then, to solve this problem and further obtain unmatched area data, this binocular vision system was also used as two camera-projector monocular systems operated from different viewing angles at the same time to fill in missing data of the binocular reconstruction. This method involves producing measurable images by integrating such techniques as multiple exposures and high dynamic range imaging to ensure the capture of high-quality phase of each point. An image-segmentation technique was also introduced to distinguish which monocular system is suitable to reconstruct a certain lost point accurately. Our experiments demonstrate that these techniques extended the measurable areas on the high dynamic range of surface reflectivity such as specular objects or scenes with high contrast to the whole projector-illuminated field.     

Haze removal method based on a variation function and colour attenuation prior for UAV remote-sensing images

Aiming at the problem of low visibility of images obtained by UAV in hazy weather, this paper proposes an image dehazing algorithm based on variation function and colour attention prior. A large number of experiments have proved that the sky or other bright regions could affect the estimation of atmospheric light and transmittance. In the experiment, our proposed algorithm divides the images into sky and dark regions and uses the pixels of the dark region to solve the atmospheric light value. According to the region where the pixels are located, the transmittances of the pixels in the sky and non-sky regions are separately estimated and adjusted. The experiment’s results show that the restored image visibility, information entropy and colour saturation are significantly improved, and the algorithm’s computational efficiency is high.     

Method for measuring veiling glare in high-performance display devices

An experimental method for measuring the veiling glare characteristics of display devices is presented. The measured veiling glare ratio (G) is taken to be the luminance in the surrounding bright field divided by the luminance in a dark circle. The method is based on a collimated conic probe that minimizes signal contamination from bright surroundings allowing for measurements of low luminance in a circular dark spot of a test pattern. A correction factor computed with test patterns having opaque spots is introduced. The factor is expressed as a bivariate function of the dark-spot radius and the distance between the probe and the emissive surface. We studied the uncertainty introduced by the method by measuring veiling glare test patterns printed on radiographic film for which the transmission of the dark spots was determined experimentally. Performance characterization measurements show that signal contamination is less than 10(-4) of the bright field surrounding a dark circle. Our results show that G of a few hundred can be measured with an uncertainty of a few percent, and ratios of approximately 10(3) can be reported within 10%. Finally, we demonstrate the method by measuring G for a high-performance monochrome cathode-ray tube display.     

Time course of brightness under transient glare condition

It was shown that a peripheral glare source reduces the brightness of a foveal stimulus. We hypothesized that this brightness reduction is governed by an inhibitory effect of the glare source on the test. We reported the results of an investigation of the dynamic of brightness reduction of an incremental stimulus immediately after the onset of a glare source in the field of view. A magnitude comparison paradigm using constant stimuli was adopted to determine the luminance that appeared equal in brightness to the standard patch. The luminance of the standard stimulus was in the mesopic range (0.5 cd/m2), and the levels of glare were 15 and 60 lx. Results showed that the time course of brightness reduction followed the typical shape attributed to the Broca-Sulzer effect. Data were fitted with a model that first considers the response of a peripheral ganglion cell to glare and then its inhibitory effect on the test signals. We discussed the plausibility of a postretinal stage of processing.     

Testing the limitations of 2-D companding for strain imaging using phantoms

Companding may be used as a technique for generating low-noise strain images. It involves warping radio-frequency echo fields in two dimensions and at several spatial scales to minimize decorrelation errors in correlation-based displacement estimates. For the appropriate experimental conditions, companding increases the sensitivity and dynamic range of strain images without degrading contrast or spatial resolution significantly. In this paper, we examine the conditions that limit the effectiveness of 2-D local companding through a series of experiments using phantoms with tissue-like acoustic and elasticity properties. We found that strain noise remained relatively unchanged as the applied compression increased to 5% of the phantom height, while target contrast increased in proportion to the compression. Controlling the image noise at high compressions improves target visibility over the broad range induced in elastically heterogeneous media, such as biological tissues. Compressions greater than 5% introduce large strains and complex motions that reduce the effectiveness of companding. Control of boundary conditions and ultrasonic data sampling rates is critical for a successful implementation of our algorithms.     

Perceptually inspired HDR images tone mapping with color correction

In this article we present a novel tone mapping operator (TMO) for high dynamic range (HDR) images. Starting from an algorithm for low dynamic range image enhancement and color correction called ACE (automatic color enhancement), we keep its differential and local behavior, introducing new features to correctly handle the high variation of HDR images. In particular, we add a nonlinear local regulator able to automatically tune the algorithm parameters on image variations. In this way, the algorithm behavior changes according to local variations. Moreover, a key setting feature has been added to control the output appearance; it automatically proposes an appropriate key value for the final spatial invariant display mapping. The proposed method performs the spatial variant filtering using only one parameter, that tunes output detail visibility versus overall contrast. We propose a default setting, that guarantees a good solution in most cases. Test, results, and comparison are presented. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 285–294, 2007     

基于阈值增量的标准动态眩光源设计方法

针对目前眩光测量装置面临的测量标准不统一的问题,提出了一种基于阈值增量(TI)的标准动态眩光源设计方法,建立了眩光测量仪校准系统.依据阈值增量的测量要求确定标准动态眩光源结构;眩光测量过程中,在保证实验室环境和现实路灯照明环境中的位置指数与立体角分别相等的前提下,规划眩光源的布局以及确定眩光源的发光面积;以最高为24 ...     

Facile Synthesis of Monodispersed Polysulfide Spheres for Building Structural Colors with High Color Visibility and Broad Viewing Angle

The synthesis and assembly of monodispersed colloidal spheres are currently the subject of extensive investigation to fabricate artificial structural color materials. However, artificial structural colors from general colloidal crystals still suffer from the low color visibility and strong viewing angle dependence which seriously hinder their practical application in paints, colorimetric sensors, and color displays. Herein, monodispersed polysulfide (PSF) spheres with intrinsic high refractive index (as high as 1.858) and light‐absorbing characteristics are designed, synthesized through a facile polycondensation and crosslinking process between sodium disulfide and 1,2,3‐trichloropropane. Owing to their high monodispersity, sufficient surface charge, and good dispersion stability, the PSF spheres can be assembled into large‐scale and high‐quality 3D photonic crystals. More importantly, high structural color visibility and broad viewing angle are easily achieved because the unique features of PSF can remarkably enhance the relative reflectivity and eliminate the disturbance of scattering and background light. The results of this study provide a simple and efficient strategy to create structural colors with high color visibility, which is very important for their practical application.     

Analysis Of Repeatability For Measurements Of Veiling Glare Index

Various factors that affect the repeatability of an apparatusfor the measurement of veiling glare index of a long focal length opticalsystem are discussed,which include the errors influencing the radianceuniformity of the extended bright field,positions of the detector,measuring aperture,and the black patch.The results can be used in thedesign of any veiling glare measurement apparatus.     

Pilot study into optimisation of viewing conditions for electronically displayed images

The increased use of soft-copy reporting introduces new concerns over the effect of viewing conditions on the observer's ability to report images. Owing to their lower luminance, electronic display screens may be more susceptible to poor viewing conditions than conventional viewing boxes and there is the potential for images to be displayed in locations not optimised for viewing radiographs. In the present work, the effects of sub-optimal viewing conditions on the observer's performance for images on an electronic display device are investigated. A test object was used to produce a computed radiography image containing a wide range of grey levels. The image was scored under quasi-ideal and sub-optimal conditions and the effect of changing the viewing conditions on the observer's performance determined. Basic photometric quantities were used to characterise the viewing conditions and the degradation in observer performance related to these quantities. The presence of structured reflection had a significant effect on the observer's ability to discern low-contrast objects. The study demonstrates the need for adequate viewing conditions especially when images are displayed on low luminance devices in sub-optimal conditions.     

Post-beamforming second-order Volterra filter for pulse-echo ultrasonic imaging

We present a new algorithm for deriving a second-order Volterra filter (SVF) capable of separating linear and quadratic components from echo signals. Images based on the quadratic components are shown to provide contrast enhancement between tissue and ultrasound contrast agents (UCAs) without loss in spatial resolution. It is also shown that the quadratic images preserve the low scattering regions due to their high dynamic range when compared with standard B-mode or harmonic images. A robust algorithm for deriving the filter has been developed and tested on real-time imaging data from contrast and tissue-mimicking media. Illustrative examples from image targets containing contrast agent and tissue-mimicking media are presented and discussed. Quantitative assessment of the contrast enhancement is performed on both the RF data and the envelope-detected log-compressed image data. It is shown that the quadratic images offer levels of enhancement comparable or exceeding those from harmonic filters while maintaining the visibility of low scattering regions of the image.     

Multiscale gradient domain compression for astronomical high dynamic range imaging

Visualisation of high dynamic range images requires compression of the data to be properly displayed on media with more limited dynamic ranges. Astronomical images pose a difficult challenge for dynamic range compression algorithms, due to the nature of the imaged objects and to the lack of a reflectance illumination model based on spatial frequencies. As a result, most of the algorithms commonly used for daylight high dynamic range compression fail in achieving an optimal visualisation of astronomical targets. We propose an extended multiscale algorithm based on compression of the dynamic range in the gradient domain. Our algorithm effectively compresses the dynamic range, enhances local contrast and avoids noise amplification. This is achieved with a multiscale representation of the image and the use of luminance information. Our results show a significantly improved visualisation of astronomical images compared to the standard gradient domain compression, as well as more robustness to noise and better artefact suppression.     

基于卷积神经网络的LDR图像重建HDR图像的方法研究

目的为了在高动态范围成像技术中更简单、有效地拓展图像的动态范围,提出一种基于低动态(LDR)图像重建高动态(HDR)图像的算法。方法基于扩张卷积层的卷积深度神经网络模型,提出一种根据相同场景中各种照明与曝光的LDR图像组来建立HDR图像新模型的图像融合算法。结果通过所提出的LDR和不同比特深度HDR映射关系,采用链式结构完成了从LDR图像到HDR图像的重建。结论通过拟建的HDRI模型,拓宽了图像的动态范围,并提高了物理光信息恢复能力。与传统算法相比,该研究所提出的方法能减少运算量,能较好地还原高动态范围场景。     

Simulation of the viewing properties and optical compensation of the biaxial nematic in-plane switching mode

Using Berreman 4 × 4 optical methods and continuum theory, we investigate the theoretical viewing properties of a potential homeotropically aligned biaxial nematic display switched with in-plane fields. We determine the isocontrast, isotransmission viewing characteristics for wide-angle viewing for in-plane switching and consider the necessary requirements for optical compensation to produce a high transmission in the bright state and low transmission in the dark state. We show how compensation can be achieved with biaxial compensation layers using a homogeneous biaxial film or from birefringence.     

Laser Glare in the Cockpit: Psychophysical Estimates versus Model Predictions of Veiling Luminance Distribution

Two methods for estimating the visual effects of light scattered from a laser glare source were compared: (1) a veiling luminance (VL) model that convolves a radiometric scan of the corneal light distribution with a point-spread function to calculate the retinal distribution and (2) psychophysically determined equivalent background luminance (EBL). For six subjects, detection thresholds for a 12-arc-min-diameter test spot were measured at 24 points in the glare field (4 quadrants x 6 eccentricities between 0.25 and 8 deg). Measured Weber fractions were used to calculate EBL's for each test point. Output of the VL model matched the EBL data well, but underestimated the EBL at the smallest (0.25-deg) eccentricity and overestimated it at eccentricities from 1 to 4 deg. This model can be a useful predictor of visual decrements in a variety of glare situations.     

A Post-Processing Algorithm for Boosting Contrast of MRI Images

Low contrast of Magnetic Resonance (MR) images limits the visibility of subtle structures and adversely affects the outcome of both subjective and automated diagnosis. State-of-the-art contrast boosting techniques intolerably alter inherent features of MR images. Drastic changes in brightness features, induced by post-processing are not appreciated in medical imaging as the grey level values have certain diagnostic meanings. To overcome these issues this paper proposes an algorithm that enhance the contrast of MR images while preserving the underlying features as well. This method termed as Power-law and Logarithmic Modification-based Histogram Equalization (PLMHE) partitions the histogram of the image into two sub histograms after a power-law transformation and a log compression. After a modification intended for improving the dispersion of the sub-histograms and subsequent normalization, cumulative histograms are computed. Enhanced grey level values are computed from the resultant cumulative histograms. The performance of the PLMHE algorithm is compared with traditional histogram equalization based algorithms and it has been observed from the results that PLMHE can boost the image contrast without causing dynamic range compression, a significant change in mean brightness, and contrast-overshoot.     

Precision and Accuracy in Scientific Imaging

Digital images are commonly used to represent scientific data. Typically, high resolution images with many square pixels are considered to be necessary under the assumption that the increased precision of such images yields increased accuracy to the viewer. We question this assumption by demonstrating improved accuracy in viewing digital images without requiring increased resolution by demonstrating how pixels with variable shapes chosen to best represent an image constitute a significant improvement over the square pixels in enhancing the accuracy of viewing such digital images.