Xiaoyang Mao

Image-guided streamline placement on curvilinear grid surfaces

The success of using a streamline technique for visualizing a vector field usually depends largely on the choice of adequate seed points. G. Turk and D. Banks (1996) developed an elegant technique for automatically placing seed points to achieve a uniform distribution of streamlines on a 2D vector field. Their method uses an energy function calculated from the low-pass filtered streamline image to guide the optimization process of the streamline distribution. This paper proposes a new technique for creating evenly distributed streamlines on 3D parametric surfaces found in curvilinear grids. We make use of Turk and Bankss 2D algorithm by first mapping the vectors on a 3D surface into the computational space of the curvilinear grid. To take into the consideration the mapping distortion caused by the uneven grid density in a curvilinear grid, a new energy function is designed and used for guiding the placement of streamlines in the computational space with desired local densities.

Splatting of non rectilinear volumes through stochastic resampling

The paper extends the conventional splatting algorithm for volume rendering non rectilinear grids. A stochastic sampling technique called Poisson sphere/ellipsoid is employed to adaptively resample a non rectilinear grid with a set of randomly distributed points whose energy support extents are well approximated by spheres or ellipsoids. Then volume rendered images can be generated by splatting the scalar values at the new sample points with filter kernels corresponding to these spheres and ellipsoids. Experiments have been carried out to investigate the image quality as well as the time/space efficiency of the new approach, and the results suggest that our approach can be regarded as an alternative for existing fast volume rendering techniques of non rectilinear grids.

Watermarking 3D geometric models through triangle subdivision

Digital water marking, the technique for hiding information into multimedia contents, is attracting large attentions in the recent years. This paper proposes a new water marking technique for 3D geometric models. The new algorithm retriangulates a part of a triangle mesh and embeds the watermark into the positions of the newly added vertices. Up to 8 bytes data can be invisibly embedded into an edge of the triangle mesh without causing any changes to the geometry of the original 3D model. The embedded watermark resists affine transformation and can be extracted only from the stego-model without using the original cover model.

Splatting of curvilinear volumes

The paper presents a splatting algorithm for volume rendering of curvilinear grids. A stochastic sampling technique called Poisson sphere/ellipsoid sampling is employed to adaptively resample a curvilinear grid with a set of randomly distributed points whose energy support extents are well approximated by spheres and ellipsoids. Filter kernels corresponding to these spheres and ellipsoids are used to generate the volume rendered image of the curvilinear grid with a conventional footprint evaluation algorithm. Experimental results show that our approach can be regarded as an alternative to existing fast volume rendering techniques of curvilinear grids.

Real-time feature-aware video abstraction

This paper presents a novel feature-aware rendering system that automatically abstracts videos and images with the goal of improving the effectiveness of imagery for visual communication tasks. We integrate the bilateral grid to simplify regions of low contrast, which is faster than the separable approximation to the bilateral filter, and use a feature flow-guided anisotropic edge detection filter to enhance regions of high contrast. The edges detected in this paper are smoother, more coherent and stylistic than those of the isotropic difference-of-Gaussian filter. The presented algorithms are highly parallel, allowing a real-time performance on modern GPUs. The implementation of our approach is straightforward. Several experimental examples are given at the end of the paper to demonstrate the effectiveness of our approach.

Using multiple data sources to get closer insights into user cost and task performance

This pilot study explores the use of combining multiple data sources (subjective, physical, physiological, and eye tracking) in understanding user cost and behavior. Specifically, we show the efficacy of such objective measurements as heart rate variability (HRV), and pupillary response in evaluating user cost in game environments, along with subjective techniques, and investigate eye and hand behavior at various levels of user cost. In addition, a method for evaluating task performance at the micro-level is developed by combining eye and hand data. Four findings indicate the great potential value of combining multiple data sources to evaluate interaction: first, spectral analysis of HRV in the low frequency band shows significant sensitivity to changes in user cost, modulated by game difficulty-the result is consistent with subjective ratings, but pupillary response fails to accord with user cost in this game environment; second, eye saccades seem to be more sensitive to user cost changes than eye fixation number and duration, or scanpath length; third, a composite index based on eye and hand movements is developed, and it shows more sensitivity to user cost changes than a single eye or hand measurement; finally, timeline analysis of the ratio of eye fixations to mouse clicks demonstrates task performance changes and learning effects over time. We conclude that combining multiple data sources has a valuable role in human-computer interaction (HCI) evaluation and design.

A gaze and speech multimodal interface

Eyesight and speech are two channels that humans naturally use to communicate with each other. However both the eye tracking and the speech recognition technique available today are still far from perfect. Our goal is find how to effectively make use of these error-prone information from both modes, in order to use one mode to correct errors of another mode, overcome the immature of recognition techniques, resolve the ambiguity of the users speaking, and improve the interaction speed. The integration strategies and the evaluation experiment demonstrate that these two modalities can be used multimodally to improve the usability and efficiency of user interface, which would not be available to speech-only or gaze-only systems.

Line Integral Convolution for 3D Surfaces

Line Integral Convolution (LIC) is a very powerful vector field visualization technique as it can effectively reveal the global and complex structures of a flow field. All the existing LIC algorithms, however, requires the one-to-one correspondence between input image pixels and grid cells, and hence restrict their use only for 2D/3D structured grids. In this paper, we present a new algorithm, for convolving solid white noise on triangle meshes in 3D space, and extend. LIC for visualizing the vector field on any arbitrary 3D surfaces, such as a contour surface output from the Marching Cube algorithm, or a surface of a 3D object represented implicitly by a part of a curvilinear or an unstructured grid.

Real-time saliency-aware video abstraction

Existing real-time automatic video abstraction systems rely on local contrast only for identifying perceptually important information and abstract imagery by reducing contrast in low-contrast regions while artificially increasing contrast in higher contrast regions. These methods, however, may fail to accentuate an object against its background for the images with objects of low contrast over background of high contrast. To solve this problem, we propose a progressive abstraction method based on a region-of-interest function derived from an elaborate perception model. Visual contents in perceptually salient regions are emphasized, whereas the background is abstracted appropriately. In addition, the edge-preserving smoothing and line drawing algorithms in this paper are guided by a vector field which describes the flow of salient features of the input image. The whole pipeline can be executed automatically in real time on the GPU, without requiring any user intervention. Several experimental examples are shown to demonstrate the effectiveness of our approach.

Colored pencil filter with custom colors

This paper presents a new technique for automatically converting digital images into colored pencil drawings. In real colored pencil drawing, artists use different colors for different regions, and add pure colors directly onto paper to build the target color through optical blending. To support such effect, our technique extends the existing technique for reproducing color image with custom inks to automatically select the best color set for individual regions in a source image. Then layers of stroke image for each color are generated and superimposed with the Kubelka-Munk optical compositing model. We also allow users to specify regions and to customize the color set for a specified region interactively. The proposed technique can be easily extended to simulate other artistic media featured with optical color blending, such as pastel and wax crayons.