General perceptual contrast metric

We used video playback of courting male Schizocosa ocreata wolf spiders to examine responses of intended receivers (conspecific females) and eavesdroppers (competitor males, predatory spiders, toads) to manipulations of spider color (natural color, monochromatic gray, monochromatic RBG average) displayed against complex leaf litter backgrounds (color, grayscale). Models of chromatic and achromatic contrast between spider stimuli and backgrounds were used to predict receiver responses. The results support the hypothesis that interactions between spider and background coloration affect detection and recognition, although responses varied with receiver type. Detection responses of intended receivers (female S. ocreata) did not fit predictions of the chromatic contrast model in some cases, but showed a fair fit to the achromatic model. Detection responses of social eavesdroppers (male S. ocreata) fit the chromatic and achromatic contrast models slightly better than did female responses (poor fit and very good fit, respectively). Eavesdropping wolf spider predators (Rabidosa) exhibited detection responses that significantly matched predictions of the chromatic (very good fit) and achromatic (excellent fit) models. Whereas jumping spiders (Phidippus) showed a good fit to the chromatic and achromatic contrast models, toad predators had a good fit only to the chromatic model. Recognition responses revealed a different pattern of fit to the chromatic and achromatic models across receiver types, although Rabidosa again indicated a significant fit to both models. Taken together, the results of this study identify both chromatic and achromatic features of spider appearance as likely explanations for differences in behavioral responses of intended and unintended receivers. This outcome suggests the possibility that both sexual and natural selection likely target different features of male appearance during courtship.

This study presents the first azimuth cutoff analysis in Synthetic Aperture Radar (SAR) altimetry, aiming to assess its applicability in characterizing sea-state dynamics. In SAR imaging, the azimuth cutoff serves as a proxy for the shortest waves, in terms of wavelength, that can be detected by the satellite under certain wind and wave conditions. The magnitude of this parameter is closely related to the wave orbital velocity variance, a key parameter for characterizing wind-wave systems. We exploit wave modulations exhibited in the tail of fully-focused SAR waveforms and extract the azimuth cutoff from the radar signal through the analysis of its along-track autocorrelation function. We showcase the capability of Sentinel-6A in deriving these two parameters based on analyses in the spatial and wavenumber domains, accompanied by a discussion of the limitations. We use Level-1A high-resolution Sentinel-6A data from one repeat cycle (10 days) globally to verify our findings against wave modeled data. In the spatial domain analysis, the estimation of azimuth cutoff involves fitting a Gaussian function to the along-track autocorrelation function. Results reveal pronounced dependencies on wind speed and significant wave height, factors primarily determining the magnitude of the velocity variance. In extreme sea states, the parameters are underestimated by the altimeter, while in relatively calm sea states and in the presence of swells, a substantial overestimation trend is observed. We introduce an alternative approach to extract the azimuth cutoff by identifying the fall-off wavenumber in the wavenumber domain. Results indicate effective mitigation of swell-induced errors, with some additional sensitivity to extreme sea states compared to the spatial domain approach.

With the rapid development of urban areas, construction areas are constantly appearing. Those changed areas require timely monitoring to provide up-to-date information for urban planning and mapping. As a result, it is a challenge to develop an effective change detection technique. In this work, a method for detecting building changes from multitemporal high-resolution aerial images is proposed. Different from traditional methods, which usually depict building changes in the color domain (e.g., using pixel values or its variants as features), this work focuses on analyzing building changes in the spatial domain. Moreover, contextual relations are explored as well, in order to achieve a robust detection result. In detail, corners are first extracted from the image and an irregular Markov random field model is then constructed based on them. Energy terms in the model are appropriately designed for describing the geometric characteristics of the building. Change detection is treated as a classification process, so that the optimal solution indicates corners belonging to changed buildings. Finally, changed areas are illustrated by linking preserved corners followed by postprocessing steps. Experimental results demonstrate the capabilities of the proposed method for change detection.

Light field rendering (LFR) is an image-based rendering method for synthesizing free-viewpoint images from a set of multi-view images. In LFR, no/little knowledge of geometry is required, since scene objects are assumed to be at a constant depth. This assumption causes focus-like effects on synthetic images, in which only the objects near to the assumed depth are synthesized clearly and sharply. In order to generate all-in-focus synthetic images, the authors proposed a focus measurement method which uses several kinds of reconstruction filters. Using this method, we can detect in-focus parts on multiple images that are synthesized with different assumed depths, and integrate them into one final image. Though this algorithm was shown to be effective for some real scenes, the optimal combination of reconstruction filters has not been discussed yet. In this paper, we introduce a detailed spatial domain analysis of this focus measurement method, and compare three combinations by the theoretical analysis and an experiment.

The authors consider a stripline geometry in which a metallized filter structure shielded by a top and a bottom ground plane is located between two dielectric layers. Located on plane z=0 the metallized structure consists of an input, an output transmission-line, and a finite number of coupling strips with arbitrary width, length, and spacing. The authors present a spatial and a spectral domain approach developed to determine the scattering parameters of the class of problems sketched above. Both concepts implemented are well-posed and lead, up to discretization errors, to identical numerical results. However, the spatial domain analysis is faster by an order of magnitude. The reason for this is twofold: (a) the associated Green's function in the spatial domain can be constructed in series form containing only tabulated functions; and (b) one can show that the convergence rate of this series can be improved significantly. As an example, a passband filter structure is analyzed by the spatial domain method. >

Recent work on the psychophysics of reading has concentrated primarily on achromatic (or luminance) contrast factors (Legge et al, 1985, 1986, 1987). In general, reading is fastest with text of high contrast defined by luminance contours. In the real world, however, chromatic as well as luminance edges abound. While several studies have examined the interaction of chromatic and luminance contrasts on stimuli near threshold (e.g., Mullen, 1987; Knoblauch et al, 1984; Jameson, 1985; Switkes et al, 1988), only a few have investigated suprathreshold levels. Legge et al, (1986) demonstrated that for observers with normal vision, the luminance contrast and not the color of text on a dark background determines reading rate. This finding is consistent with threshold studies that show that the color of a grating does not affect luminance contrast sensitivity either (Nelson and Halberg, 1979), provided that one avoids frequencies near the diffraction limit (Pokorny et al, 1968; Van Nes and Bouman, 1967).

The effect of spatio-temporal chromatic and achromatic contrast on VEPs

Contour adaptation reduces the spreading of edge induced colors

There are many applications, such as pilot training, mission rehearsal, and hardware-in-the-loop simulation, which require the generation of realistic images of terrain and man-made objects in real-time. One well-known approach to meeting this requirement is to drape photo-texture over a planar polygon model of the terrain. The real time system then computes, for each pixel of the output image, the address in a texture map based on the intersection of the line-of-sight vector with the terrain model. High quality image generation requires that the terrain be modeled with a fine mesh of polygons while hardware costs limit the number of polygons which may be displayed for each scene. The trade-off between these conflicting requirements must be made in real-time because it depends on the changing position and orientation of the pilot's eye point or simulated sensor. The traditional approach is to develop a data base consisting of multiple levels of detail (LOD), and then selecting for display LOD's as a function of range. This approach could lead to both anomalies in the displayed scene and inefficient use of resources. In this paper, a new approach has been developed in which the terrain is modeled with a set of polygons and organized as a graph with each node corresponding to a polygon. This graph is pruned to select the optimum set of nodes for each eye-point position. The novelty of the proposed graph pruning lies in the coherence suggested in the selection of terrain LODs and texture LODs. The error in terrain representation is expressed in terms of the error in the texture pixels. This allows different error criteria to be used for different applications. Texas 76019 As the point of view moves, the visibility of some nodes drops below the limit of perception and may be deleted while new nodes must be added in regions near the eye point. Our pervious work has been generalized to include the case where the refinements of the polygonization are not simply nested and the graph is not a simple tree. This generalization prevents the occurrence of gaps in terrain representation.

Network segmentation is foundational and critical to traffic safety analysis. Existing approaches to conduct segmentation require engineering judgement and are subject to a lack of standard metrics for assessing segmentation performance. This paper presents a novel methodology for data-driven analytics of crash distribution, crash aggregation, and network segmentation. It provides general solutions to determine optimal segment lengths for rigorous safety analysis, and extends the knowledge of crash distribution and aggregation for innovating segment-based safety analysis. The methodology is based on a redesigned spectral analysis of crash density in the spatial frequency domain (SFD) in which frequency components represent the natural patterns how crashes occur along roadways. By proposing the one-dimensional spatial frequency domain analysis (SFDA), this paper reveals the characteristic of power spectral concentration within the low frequency band for crash distribution. Based on this finding, this paper further proposes the power spectral segment length (PSSL) for determining optimal segment lengths and the power spectral percentage (PSP) for assessing the segmentation performance. Based on those new concepts and inferences, the paper proposes the low-pass filtering (LPF) method that outperforms the sliding window (SW) method, and the improved wavelet-based method that identifies high-risk segments properly. Those new techniques are easy to implement and ready for practical application. This research illustrates that interdisciplinary and innovative analytics combined with high-quality data collected by intelligent transportation infrastructure can reshape the fundamental knowledge and conventional paradigms in traffic safety.

According to the equivalence principle, the design of the compact range (CR) reflector can be transformed into the design of its aperture. Therefore the analysis of the CR performance variations caused by the mechanical and electrical defects can be transformed into the analysis of the aperture near-field in the spatial and angular domains. Based on a square aperture and a well-designed serrated-edge aperture, the near-field characteristics have been analysed when typical amplitude and phase non-uniformities have been induced in the aperture. The aperture field convolution method and plane wave spectrum method have been adopted. Simulation results have been presented and compared in detail. The width and height of the apertures are 150 wavelengths in free space. The amplitude and phase non-uniformities discussed include: amplitude taper, serrated edge, periodic amplitude, periodic phase, linear amplitude, linear phase, local amplitude mutation and local phase mutation. The conclusions provide references for CR design, testing, measurements and antenna tolerance analysis.

The phase-shifting point diffraction interferometer (PS/PDI) is so far the most accurate measurement tool in atwavelength interferometry of projection optics for extreme ultraviolet lithography (EUVL). The complicate interrelationships between configuration parameters of PS/PDI call for an optimization to achieve high accuracy of PS/PDI. In this paper, a novel system-level modeling approach is proposed to optimize the parameters of PS/PDI designed for visible light (λ=632.8nm) concept proof experiment. The optimal reference pinhole size selection is performed by modeling pinhole spatial filtering effect using Diffraction-Based Beam Propagation (BPR) module of CODE V and in house software. The result shows that various pinhole diameters ranging from 1.6um to 2.2um should be used in our PS/PDI experiment. The test window size and grating duty cycle optimization, which is based on the spatial frequency domain analysis of PS/PDI, is conducted by modeling the entire PS/PDI system using Physical Optics Propagation (POP) module of Zemax and in house software. The optimal window size is approximately 62um for a given window-pinhole separation of 63.3um. The optimal duty cycle of grating is calculated to be 83% to obtain the maximum fringe contrast of 0.879.

The measurement of achromatic sensitivity has been an important tool for monitoring subtle changes in vision as the result of disease or response to therapy. In this study, we aimed to provide a normative data set for achromatic and chromatic contrast sensitivity functions within a common cone contrast space using an abbreviated measurement approach suitable for clinical practice. In addition, we aimed to provide comparisons of achromatic and chromatic binocular summation across spatial frequency. We estimated monocular cone contrast sensitivity functions (CCSFs) using a quick Contrast Sensitivity Function (qCSF) approach for achromatic as well as isoluminant, L/M cone opponent, and S cone opponent stimuli in a healthy population of 51 subjects. We determined the binocular CCSFs for achromatic and chromatic vision to evaluate the degree of binocular summation across spatial frequency for these three different mechanisms in a subset of 20 subjects. Each data set shows consistent contrast sensitivity across the population. They highlight the extremely high cone contrast sensitivity of L/M cone opponency compared with the S-cone and achromatic responses. We also find that the two chromatic sensitivities are correlated across the healthy population. In addition, binocular summation for all mechanisms depends strongly on stimulus spatial frequency. This study, using an approach well suited to the clinic, is the first to provide a comparative normative data set for the chromatic and achromatic contrast sensitivity functions, yielding quantitative comparisons of achromatic, L/M cone opponent, and S cone opponent chromatic sensitivities as a function of spatial frequency.

One of the most effective ways of previewing a digital video sequence is by selecting a number of relevant images, or key-frames, and organising them in a hierarchical structure in which similar images have same parents. This way, the video content can be previewed at different levels of detail by choosing a certain way of parsing the hierarchical key-frame structure. A key issue here is to define an appropriate measure for image similarity. In this article we present a way of defining asymmetric similarity measures for comparing the visual content of images, and how to use these measures for hierarchical clustering of video key-frames.

A fast and robust sliding mode controller for automatic voltage regulators in electrical power systems