It is a difficult task to design transfer functions for noisy data. In traditional transfer-function spaces, data values of different materials overlap. In this paper we introduce a novel statistical transferfunction space which in the presence of noise, separates different materials in volume data sets. Our method adaptively estimates statistical properties, i.e. the mean value and the standard deviation, of the data values in the neighborhood of each sample point. These properties are used to define a transfer-function space which enables the distinction of different materials. Additionally, we present a novel approach for interacting with our new transferfunction space which enables the design of transfer functions based on statistical properties. Furthermore, we demonstrate that statistical information can be applied to enhance visual appearance in the rendering process. We compare the new method with 1D, 2D, and LH transfer functions to demonstrate its usefulness.
Figure 1: Non-photorealistic shadows expressed in blue tones: (a) lungs and (b) ankles from the visible female CT dataset, and (c) 3D cardiac ultrasound.
AbstractSoft shadows are effective depth and shape cues. However, traditional shadowing algorithms decrease the luminance in shadow areas. The features in shadow become dark and thus shadowing causes information hiding. For this reason, in shadowed areas, medical illustrators decrease the luminance less and compensate the lower luminance range by adding color, i.e., by introducing a chromatic component. This paper presents a novel technique which enables an interactive setup of an illustrative shadow representation for preventing overdarkening of important structures. We introduce a scalar attribute for every voxel denoted as shadowiness and propose a shadow transfer function that maps the shadowiness to a color and a blend factor. Typically, the blend factor increases linearly with the shadowiness. We then let the original object color blend with the shadow color according to the blend factor. We suggest a specific shadow transfer function, designed together with a medical illustrator which shifts the shadow color towards blue. This shadow transfer function is quantitatively evaluated with respect to relative depth and surface perception.
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