Graphical Tasks Research Articles

Dynamic Range Reduction Inspired by Photoreceptor Physiology

A common task in computer graphics is the mapping of digital high dynamic range images to low dynamic range display devices such as monitors and printers. This task is similar to the adaptation processes which occur in the human visual system. Physiological evidence suggests that adaptation already occurs in the photoreceptors, leading to a straightforward model that can be easily adapted for tone reproduction. The result is a fast and practical algorithm for general use with intuitive user parameters that control intensity, contrast, and level of chromatic adaptation, respectively.

Feature-based surface parameterization and texture mapping

Surface parameterization is necessary for many graphics tasks: texture-preserving simplification, remeshing, surface painting, and precomputation of solid textures. The stretch caused by a given parameterization determines the sampling rate on the surface. In this article, we present an automatic parameterization method for segmenting a surface into patches that are then flattened with little stretch. Many objects consist of regions of relatively simple shapes, each of which has a natural parameterization. Based on this observation, we describe a three-stage feature-based patch creation method for manifold surfaces. The first two stages, genus reduction and feature identification, are performed with the help of distance-based surface functions. In the last stage, we create one or two patches for each feature region based on a covariance matrix of the feature's surface points. To reduce stretch during patch unfolding, we notice that stretch is a 2 × 2 tensor, which in ideal situations is the identity. Therefore, we use the <i>Green-Lagrange tensor</i> to measure and to guide the optimization process. Furthermore, we allow the boundary vertices of a patch to be optimized by adding <i>scaffold triangles</i>. We demonstrate our feature-based patch creation and patch unfolding methods for several textured models. Finally, to evaluate the quality of a given parameterization, we describe an image-based error measure that takes into account stretch, seams, smoothness, packing efficiency, and surface visibility.

A new CAD mesh segmentation method, based on curvature tensor analysis

This paper presents a new and efficient algorithm for the decomposition of 3D arbitrary triangle meshes and particularly optimized triangulated CAD meshes. The algorithm is based on the curvature tensor field analysis and presents two distinct complementary steps: a region based segmentation, which is an improvement of that presented by Lavoue et al. [Lavoue G, Dupont F, Baskurt A. Constant curvature region decomposition of 3D-meshes by a mixed approach vertex-triangle, J WSCG 2004;12(2):245–52] and which decomposes the object into near constant curvature patches, and a boundary rectification based on curvature tensor directions, which corrects boundaries by suppressing their artefacts or discontinuities. Experiments conducted on various models including both CAD and natural objects, show satisfactory results. Resulting segmented patches, by virtue of their properties (homogeneous curvature, clean boundaries) are particularly adapted to computer graphics tasks like parametric or subdivision surface fitting in an adaptive compression objective.

Decreased Movement Speed in Girls with Turner Syndrome: A Problem in Motor Planning or Muscle Initiation?

In three experiments with graphical tasks we examined whether the decreased movement speed in girls with Turner Syndrome (TS) is caused either by a diminished planning capacity or by more peripheral motor execution problems. Fourteen girls with TS and 14 matched controls (mean age 11.6 years) participated. Task difficulty addressed the muscle-initiation, size-control, and shape-programming level (Van Galen, 1991). The influence of task difficulty on accuracy, velocity, velocity profile and dwell time was analyzed and confirmed that girls with TS do not plan and program their movements differently from normals. We conclude that the decreased movement speed in TS is caused by problems at the muscle initiation level.

Muscular co-contraction covaries with task load to control the flow of motion in fine motor tasks

This study focuses on the relationship between movement-time fluctuations in fine motor tasks and changing levels of muscular co-contraction. Based on a recent neuromotor noise theory, we expected that increased task stress would increase muscular co-contraction and prolong movement times. Ten right-handed adults performed a graphic task, which elicited local movement-time prolongations. In half the trials, a distracting sound was presented as an external stressor. Besides pen-tip kinematics, two estimates of muscular co-contraction were obtained from the surface EMG measurements of eight arm and hand muscles. The results confirm the presumed co-variation of movement time and co-contraction. We conclude that muscular co-contraction forms a strategic means to adapt the flow of motion to central information processing demands.

Iso-phote based adaptive surface fitting to digitized points and its applications in region-based tool path generation, slicing and surface triangulation

An important task in computer graphics, computer-aided design and reverse engineering is the mathematical modeling of three-dimension complex surfaces based on digitized points. However, there are several open problems that are viewed as a bottleneck in the mathematical modeling. The topology is unknown. The reconstruction is based on parameterization and fitting stages. The above problems are influenced mainly by the parameterization, and the issue of parameterization for curve and surface fitting has been a difficult one since the advent of computers in design engineering. To resolve the above problems, in this paper a new strategy based on region-by-region adaptation is presented to surfaces fitting for digitized points. Furthermore, the “regions” used for adaptive surface fitting can be applied extendedly to three industrial applications: (1) tool path generation; (2) slicing; and (3) surface triangulation.

Large environment rendering using plenoptic primitives

One of the most difficult tasks in computer graphics is to enable virtual walkthroughs in very large and complicated environments that are photorealistic, seamless, and in real time. Current image-based rendering techniques, while capable of photorealism and interactive speeds, have failed in practice to extend to visualizations of such environments. We demonstrate an approach that defines a virtual walkthrough experience using plenoptic primitives (PPs). A PP can be any type of local visual experience: 360/spl deg/ static panorama, panoramic video (PV), lumigraph/light field representation, or concentric mosaics (CMs). By combining them judiciously, user experience can be authored with significantly reduced effort while maintaining high-quality user experience. We illustrate our technique on synthetic and real environments using PVs and CMs and show how the problem of achieving smooth transitions among PVs and CMs can be solved by using position-dependent local geometries.

An approach to the simulation of the sea as participating medium

The creation and rendering of realistic water scenes is a challenging task in Computer Graphics. Algorithms that reproduce the illumination and colour inside water bodies must be able to handle anisotropic media and multiple scattering. This study focuses on solving the problem of light transport using the discrete ordinates method. A general system is presented that can generate qualitative and detailed quantitative information, such as the amount of light that reaches the boundaries of the medium or that is absorbed in each voxel. It provides a quantitative estimate of the calculation error involved during the illumination calculation and can deal with anisotropic as well as highly peaked phase functions, including the spectral behaviour of the characteristic parameters of the medium. Surfaces within the medium can be taken into account, as well as their contribution to the radiance distribution. The system was applied to the oceanic medium and several simple images were calculated in different types of water. The results indicate that image generation is strongly affected by the spectral behaviour of the absorption and scattering coefficients and the correct treatment of phase functions.

The Semantic Organization Patterns of Young Children: Implications for Augmentative and Alternative Communication

The successful use of augmentative and alternative communication (AAC) systems by young children rests on the child's ability to efficiently and accurately locate desired vocabulary. Typically, young children's vocabulary items are organized on communication boards or computer displays according to what seems logical to speech-language pathologists, teachers, and parents. It remains unclear, however, whether adult-generated vocabulary arrangements truly reflect the cognitive organization of young children who require AAC. There are few empirical data to describe how young children organize vocabulary, particularly more abstract linguistic concepts. In the current study, a graphic symbol arrangement task was used to investigate how 20 children between 4;0 and 5;11 years of age organized linguistic concepts. The children were asked to organize 42 pictures depicting various familiar vocabulary items that included nouns, verbs, descriptors, prepositions, pronouns, and question words. During and after the sorting task, the children were asked to talk about the rationales for their arrangements. Results indicated that they purposefully arranged an average of 40% of vocabulary items, and tended to organize concrete items (e.g., nouns, action verbs) in pairs or small groups according to event schema. The children had greater difficulty organizing abstract items (e.g., prepositions) than concrete words (e.g., cookie). Implications for AAC interventions are discussed along with future research directions.

Robust creation of implicit surfaces from polygonal meshes

Implicit surfaces are used for a number of tasks in computer graphics, including modeling soft or organic objects, morphing, collision detection, and constructive solid geometry. Although operating on implicit surfaces is usually straightforward, creating them is not. We introduce a practical method for creating implicit surfaces from polygonal models that produces high-quality results for complex surfaces. Whereas much previous work in implicit surfaces has been done with primitives such as blobbies, we use implicit surfaces based on a variational interpolation technique (the three-dimensional generalization of thin-plate interpolation). Given a polygonal mesh, we convert the data to a volumetric representation to use as a guide for creating the implicit surface iteratively. We begin by seeding the surface with a number of constraint points through which the surface must pass. Iteratively, additional constraints are added; the resulting surfaces are evaluated, and the errors guide the placement of subsequent constraints. We have applied our method successfully to a variety of polygonal meshes and consider it to be robust.

Wrist and Shoulder Muscle Activity Changes Across Computer Tasks

The computer workstation is a ubiquitous tool in the office work environment; however, its use varies across many different tasks from surfing the Internet to typing. The question, therefore, is how does exposure to different physical risk factors for musculoskeletal disorders vary across tasks? Fifteen adults (10 females, 5 males) completed tasks simulating work at a computer workstation. The tasks were typing text, completing an html-based form, editing a document, a graphics task, and finally navigating through a series of web pages. During these tasks the muscle activity of the wrist prime movers and three shoulder muscle groups were recorded using surface EMG. For the wrist, the extensors were the most active ranging on average from 8 to 25 percent of Maximum Voluntary Contraction amplitude, with the greatest activity occurring in the typing task. The wrist activity decreased when the work changed from a keyboard-based activity to predominantly mouse-based activity. For the shoulder, the greatest activity was in the Trapezius muscle. The shoulder muscles were most active when both the mouse and the keyboard were required by the task. in summary, wrist and shoulder muscle activities at a computer workstation depend upon the type of task at hand.

Rendering Natural Waters

Creating and rendering realistic water is one of the most daunting tasks in computer graphics. Realistic rendering of water requires that the sunlight and skylight illumination are correct, the water surface is modeled accurately and that the light transport within water body is properly handled. This paper describes a method for wave generation on a water surface using a physically‐based approach. The wave generation uses data from the oceanographical observations and it is controlled by intuitive parameters such as wind speed and wind direction. The optical behavior of the water surfaces is complex but is well‐described in the ocean science literature. We present a simple and intuitive light transport approach that is easy to use for many different water types such as deep ocean water, muddy coastal water, and fresh water bodies. We demonstrate our model for a number of water and atmospheric conditions.

Understanding the use of domain and task knowledge in the interpretation of graphical displays

Given the complexity of most cognitive processes and that of the associated knowledge base, which facilitates effective and efficient use of electronic diagnostic equipment, this paper addresses the important area of understanding how human operators interact with and construct meaningful understanding from the data displayed by such devices. Some work has been done in areas related to graphical and diagrammatical information processing. However, none of these studies considered the interaction of domain and task experts’ performance on similar graphical tasks. The exploratory study presented in this paper intends to identify patterns in cognitive processes used by ultrasound operators, and to provide an explanation for the reason for such patterns in light of the structure and deployment of domain and task-knowledge. The findings illustrate the complex interrelatedness of theoretical and practical knowledge, which constitutes professional knowledge. Professional knowledge becomes more complex when individuals depend on sophisticated tools to assist in their thinking. The study suggests a possibility to think about professional knowledge as a distributed knowledge across task and domain knowledge and knowledge inherent in the tools. Such distributed knowledge in professional practice needs further exploration.

Graphical Selection of Data Views

Graphical selection of data views is a fundamental task in interactive statistical graphics. Linked plots provide a form of indirect selection, where direct manipulation of objects displayed in one plot indirectly selects objects in other plots. A pointing device or brush is typically used for direct manipulation, and so this indirect selection is commonly known as linked brushing. Most commonly, linked brushing is applied to two or more scatterplots showing various pairs of variables from a multivariable dataset. This article describes a generalization of linked brushing for the setting where plots display different, though related datasets. With this form of linking, we can graphically explore relationships between datasets. Our linking system is extensible and handles any kind of display of any kind of dataset, as well as arbitrary relationships between those datasets.

A new conceptual model of asymmetry in motor performance for bidimensional fast-oscillating movements in selected variants of performance.

Spatial characteristics and lateral differences between two upper extremities were investigated in unilateral graphical tasks involving fast oscillating movements in the vertical plane based on the model of restricted (less than 10 degrees) horizontal abduction adduction in the shoulder joint. The spatial locations of reversal points were used to identify two groups of motor performance: with big angles and gross vertical vectors (stretched accordion group), and small projectile angles with small vertical vectors (compressed accordion group). Both groups appeared in right and left arm performance. The former group had a strong pattern of distribution of big and small projectile angles which reflects a particular variant of execution with a significant difference between angles and intermittent big and small angles (BB). Two other variants of execution relating to specific angular patterns of performance were identified in the compressed accordion group: one (Bs) showed a big difference between big and small angles but without intermittance; the other (ss) had only small differences between magnitudes of angles. The Bs variant of execution was observed only in left-handed performance, whilst ss was typical of both extremities. The performances affiliated to the stretched accordion group with the BB variant of execution mostly operated with reciprocal cooperation between alterations of X and Y vectors for the right arm. Performance related to the same group with the Bs variant of execution used concurrent collaboration involving alteration of these vectors for the left arm. The compressed accordion group which deployed the ss variant of execution mostly displayed concurrent alteration of vectors irrespective of the side of performance. It is suggested that the spatial movement strategies might reflect several different schemes of motor control wherein coupling of oscillators controls vertical and horizontal movements. It is also proposed that specific subunits of the functional system of nervous elements responsible for the expression of spatial derivatives of motor programmes may exist at lower levels of the CNS and might be initiated by the left brain or by the cooperative activity of the left and right hemispheres.

Trust and Disclosure of Sexual Orientation in Gay Males' Mother-Son Relationships

ABSTRACT This study explored the possibility that changes in feelings of trust for mother are associated with gay males' decisions to disclose (or withhold) their sexual orientation in their mother-son relationships. Fifty gay and bisexual males completed a questionnaire about their coming out experiences in the context of their relationships with their mothers. As part of this questionnaire, they completed a retrospective graphical trust history task that involved plotting the degree of trust they felt for their mothers over time and across important events (such as disclosure). Results are discussed in terms of gay men's expectations about their mothers' responses to disclosure, the evidence for stability versus change in their memories regarding the nature of their feelings of maternal trust over time, the complexity of the trust histories participants drew, similarity between disclosers and non-disclosers in the shape of their trust curves, and the types of events and experiences that constituted the timeline or “plot” in the stories participants told about their mother-son relationships.This study offers the first empirical evidence to support speculations linking disclosure of sexual orientation to the climate of trust that exists in the relationship between discloser and target (e.g., Holtzen, Kenny & Mahalik, 1995).

Local Bias in Autistic Subjects as Evidenced by Graphic Tasks: Perceptual Hierarchization or Working Memory Deficit?

In the present study, copying tasks were used to assess hierarchical aspects of visual perception in a group of 10 nonsavant autistic individuals with normal intelligence. In Experiment 1, the hierarchical order of graphic construction and the constancy of this order were measured for the copying of objects and nonobjects. In comparison to control participants, autistic individuals produced more local features at the start of the copying. However, they did not differ from controls with respect to graphic constancy. Experiment 2 measured the effect of geometrical impossibility on the copying of figures. Results revealed that autistic individuals were less affected by figure impossibility than were controls. Therefore, these experiments seem to support the notion of a local bias for visual information processing in individuals with autism. Two interpretations are proposed to account for this effect. According to the hierarchical deficit hypothesis, individuals with autism do not manifest the normal global bias in perceiving scenes and objects. Alternatively, the executive function hypothesis suggests that autism brings about limitations in the complexity of information that can be manipulated in short-term visual memory during graphic planning.

Local Bias in Autistic Subjects as Evidenced by Graphic Tasks: Perceptual Hierarchization or Working Memory Deficit?

Local Bias in Autistic Subjects as Evidenced by Graphic Tasks: Perceptual Hierarchization or Working Memory Deficit?

SGI parallel technology for graphics and visualization

This paper gives an overview of developments at Silicon Graphics in the areas of scalable multiprocessing and visualization. These developments are grounded in a scalable shared memory architecture that allows a high degree of modularity and enormous flexibility of configuration. The first implementations of this architecture include graphics supercomputers with multiple processors and multiple graphics subsystems that enable parallelism at all levels, including parallelism applied to single graphics tasks. We first describe this architecture and then discuss the characteristics of its first generation implementations.

Multi-Stage N-rooks Sampling Method

Abstractxs In many graphics tasks, such as pixel antialiasing, a set of spatially “uniform” samples must be generated on a unit square. Some algorithms attempt to create sets of samples whose x and y coordinates are each themselves uniform, while making sure that the samples are also uniform in two dimensions. However, this is hard to do if the number of samples is not a perfect square. In this paper, we introduce a new sampling strategy which generates any number of uniform twodimensional samples while maintaining uniformity in x and y as well.