Pavel Slavik

Hierarchical visibility culling with occlusion trees

In the scope of rendering complex models with high depth complexity, it is of great importance to design output-sensitive algorithms, i.e., algorithms with the time complexity proportional to the number of visible graphic primitives in the resulting image. In this paper an algorithm allowing efficient culling of the invisible portion of the rendered model is presented. Our approach uses a spatial hierarchy to represent the topology of the model. For a current viewpoint a set of polygonal occluders is determined that are used to build the occlusion tree. In the occlusion tree occlusion volumes of the selected occluders are merged. Visibility from the viewpoint is determined by processing the spatial hierarchy and classifying the visibility of its regions. In this process the occlusion tree is used to determine the viewpoint-to-region visibility efficiently. The algorithm is well-suited for complex models where large occluders are present.

Non-speech input and speech recognition for real-time control of computer games

This paper reports a comparison of user performance (time and accuracy) when controlling a popular arcade game of Tetris using speech recognition or non-speech (humming) input techniques. The preliminary qualitative study with seven participants shows that users were able to control the game using both methods but required more training and feedback for the humming control. The revised interface, which implemented these requirements, was positively responded by users. The quantitative test with 12 other participants shows that humming excelled in both time and accuracy, especially over longer distances and advanced difficulty levels.

Acoustic control of mouse pointer

This paper describes the design and implementation of a system for controlling mouse pointer using non-verbal sounds such as whistling and humming. Two control modes have been implemented—an orthogonal mode (where the pointer moves with variable speed either horizontally or vertically at any one time) and a melodic mode (where the pointer moves with fixed speed in any direction). A preliminary user study with four users indicates that the orthogonal control was easier to operate and that the humming was less tiring for the users than whistling. The developed system may contribute as an inexpensive, alternative pointing device for people with motor disabilities.

Whistling User Interface (U3I)

The paper describes the design, implementation and user evaluation of a system that allows a user to control a mouse pointer through whistling or humming. The pointer can be controlled in two ways: orthogonally (the pointer can only move with variable speed either horizontally or vertically at a time) and melodically (the pointer can move with fixed speed in any direction). The user study indicates that the users thought the orthogonal control was easier to operate than the melodic control. The orthogonal control was considered useful for controlling mouse movement while the melodic control was more useful for entertainment purposes. Humming was considered less tiring than whistling. This study makes several contributions to the field. First, it is perhaps the first published study investigating the use of whistling to operate a mouse pointer. Second, the system can be used as a low-cost alternative pointing device for people with motor disabilities.

PDA based navigation system for a 3D environment

Abstract Navigation systems are an important application in the field of mobile computing. In order to increase the usability of navigation systems it is desirable to present information in a form that is most informative for the user. This paper deals with the possibility of presenting the information in a 3D form that provides the user with more information than information in a 2D form. A concept of such a navigation system is described together with all the partial problems that have to be solved. The result of the project is the implementation of a system that is fully functional and could be used in various applications. The structure of the system is very flexible, allowing the substitution of some software modules by hardware solutions.

The naturalness of reproduced high dynamic range images

The problem of visualizing high dynamic range images on the devices with restricted dynamic range has recently gained a lot of interest in the computer graphics community. Various so-called tone mapping operators have been proposed to face this issue. The field of tone mapping assumes thorough knowledge of both the objective and subjective attributes of an image. However, there no published analysis of such attributes exists so far. In this paper, we present an overview of image attributes which are used extensively in different tone mapping methods. Furthermore, we propose a scheme of relationships between these attributes, leading to the definition of an overall quality measure which we call naturalness. We present results of the subjective psychophysical testing that we have performed to prove the proposed relationship scheme. Our effort sets the stage for well-founded quality comparisons between tone mapping operators. By providing good definitions of the different attributes, comparisons, be they user-driven or fully automatic, are made possible at all.

GUI generation from annotated source code

Creating user interfaces in a common task in application development. It can become time and money consuming if the same application is to be run on more platforms with different restrictions and requirements. To reduce the development cost and time the user interface can be defined on an abstract level in the form of a task model. Explicit defining and maintaining the task model can complicate the development especially in its early stages when application prototype are built. We present a way to define a user interface on an abstract level without explicit definition of the user interface module while keeping it transparent, thus reducing the work required to make functional application prototypes. Our approach is based on derivation of a user interface module directly from an application source code enriched by abstract commands of user interaction to control the generation of the user interface.

Evaluation of two principal approaches to objective image quality assessment

Nowadays, it is evident that we must consider human perceptual properties to visualize information clearly and efficiently. We may utilize computational models of human visual systems to consider human perception well. Image quality assessment is a challenging task that is traditionally approached by such computational models. Recently, a new assessment methodology based on structural similarity has been proposed. We select two representative models of each group, the visible differences predictor and the structural similarity index, for evaluation. We begin with the description of these two approaches and models. We then depict the subjective tests that we have conducted to obtain mean opinion scores. Inputs to these tests included uniformly compressed images and images compressed non-uniformly with regions of interest. Then, we discuss the performance of the two models, and the similarities and differences between the two models. We end with a summary of the important advantages of each approach.

Context-sensitive, cross-platform user interface generation

User interfaces (UI) of software applications play a crucial part in communication with users. Attractive UIs often lead to market success, and thus there is a significant incentive to provide users with malleable UIs that can adapt as much as possible to their needs. However, such UIs require significant development and maintenance efforts. In this paper, we describe a context model based on ability-based design that is well suited to the purposes of automated UI generation. We then introduce a platform that delivers adaptive UIs across various platforms. We use runtime combinatoric optimisation to support usability and to generate context-sensitive UIs. Since the development and maintenance of such UIs can be complex, our platform integrates a module for code-inspection for data-oriented applications to reduce these efforts. It also utilises a visual editor to simplify manual UI design.

Exact regional visibility using line space partitioning

Abstract We present a new method for computing visibility from a polygonal region in the plane considering a set of line segments as occluders. The proposed method provides a comprehensive description of visibility from the given region. We represent sets of occluded rays using a hierarchical partitioning of dual space (line space). The line space partitioning is maintained by a BSP tree that provides efficient operations on the sets of lines. The implementation shows that the method is suitable for computing potentially visible sets in large scenes with various visibility characteristics.