Eurographics Conference on Visualization (EuroVis) (2015) Posters R. Maciejewski and F. Marton (Editors) Selective Saturation and Brightness for Visualizing Time-Varying Volume Data Shengzhou Luo † and John Dingliana ‡ Graphics Vision and Visualisation Group (GV2), Trinity College Dublin, Ireland Abstract Time-varying volume data is used in many areas of science and engineering. However visualizations of such data are not easy for users to visually process due to the amount of information that can be presented simultaneously. In this paper, we propose a novel visualization approach which modulates focus, emphasizing important information, by adjusting saturation and brightness of voxels based on an importance measure derived from temporal and multivariate information. By conducting a voxel-wise analysis of a number of consecutive frames, we acquire a volatility measure of each voxel. We then use intensity, volatility and additional multivariate information to determine opacity, saturation and brightness of the voxels. The method was tested in visualizing a multivariate hurricane data set. The results suggest that our approach can give the user a more detailed understanding of the data by presenting multivariate information variables in one self-contained visualization. Categories and Subject Descriptors (according to ACM CCS): I.6.9 [Simulation, Modeling, and Visualization]: Visualization—Volume visualization 1. Introduction With the development of more advanced techniques for sci- entific simulation, where various physical measurements at many time-steps can be simulated at extremely high detail, providing intuitive and effective tools for the analysis and vi- sualization of such data becomes increasingly challenging. Color mappings are often used in visualization to repre- sent various types of information. Although traditional color transfer functions are often in RGB color space, transfer functions designed in HSB (hue, saturation and brightness) color space can be more intuitive and meaningful in terms of conveying quantitative information or for classifications of the data. 2. Related Work The visualization of time-varying data is an important and active topic in the visualization community. Transfer func- tion specification for static volume data has been widely † luos@tcd.ie ‡ john.dingliana@tcd.ie studied over the years [PLB * 01]. However, less work has been done for transfer function design of time-varying data. Jankun-Kelly and Ma first studied transfer function speci- fication for time-varying data [JKM01]. Kniss and Hansen applied the techniques from multi-dimensional transfer function based volume rendering to the visualization of mul- tivariate data from weather simulations [KHGR02]. Akiba et al. [AMCH07] described three approaches for the data-fusion problem in multivariate data visualization. One approach, which is to use one variable for each color channel in RGB space, is popular because of its simplicity but is limiting due to the difficulty for viewers to interpret the resulting color. The second approach, is to use one of the values based on some criterion e.g. [HE98] use alternating sampling for rendering two volumes and this has been shown to work well for medical imaging but not for fluid flow visu- alization. The third approach is to compute a weighted sum of all the values. This approach is more flexible however this may not be guaranteed to lead to an effective visualization as blending different colors might lead to ambiguous mixing of different hues. c  The Eurographics Association 2015.