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    Implicit Representation of Inscribed Volumes
    (ACM, 2018) Sahbaei, Parto; Mould, David; Wyvill, Brian; Aydın, Tunç and Sýkora, Daniel
    We present an implicit approach for constructing smooth isolated or interconnected 3-D inscribed volumes which can be employed for volumetric modeling of various kinds of spongy or porous structures, such as volcanic rocks, pumice stones, Cancellus bones, liquid or dry foam, radiolarians, cheese, and other similar materials. The inscribed volumes can be represented in their normal or positive forms to model natural pebbles or pearls, or in their inverted or negative forms to be used in porous structures, but regardless of their types, their smoothness and sizes are controlled by the user without losing the consistency of the shapes. We introduce two techniques for blending and creating interconnections between these inscribed volumes to achieve a great flexibility to adapt our approach to different types of porous structures, whether they are regular or irregular. We begin with a set of convex polytopes such as 3-D Voronoi diagram cells and compute inscribed volumes bounded by the cells. The cells can be irregular in shape, scale, and topology, and this irregularity transfers to the inscribed volumes, producing natural-looking spongy structures. Describing the inscribed volumes with implicit functions gives us a freedom to exploit volumetric surface combinations and deformations operations effortlessly.
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    Irregular Pebble Mosaics with Sub-Pebble Detail
    (The Eurographics Association, 2019) Javid, Ali Sattari; Doyle, Lars; Mould, David; Kaplan, Craig S. and Forbes, Angus and DiVerdi, Stephen
    Pebble mosaics convey images through an irregular tiling of rounded pebbles. Past work used relatively uniform tile sizes. We show how to create detailed representations of input photographs in a pebble mosaic style; we first create pebble shapes through a variant of k-means, then compute sub-pebble detail with textured, two-tone pebbles.We use a custom distance function to ensure that pebble sizes adapt to local detail and orient to local feature directions, for an overall effect of high fidelity to the input photograph despite the constraints of the pebble style.
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    Stipple Removal in Extreme-tone Regions
    (The Eurographics Association, 2019) Azami, Rosa; Doyle, Lars; Mould, David; Kaplan, Craig S. and Forbes, Angus and DiVerdi, Stephen
    Conventional tone-preserving stippling struggles with extreme-tone regions. Dark regions require immense quantities of stipples, while light regions become littered with stipples that are distracting and, because of their low density, cannot communicate any image features that may be present. We propose a method to address these problems, augmenting existing stippling methods. We will cover dark regions with solid polygons rather than stipples; in light areas, we both preprocess the image to prevent stipple placement in the very lightest areas and postprocess the stipple distribution to remove stipples that contribute little to the image structure. Our modified stipple images have better visual quality than the originals despite using fewer stipples.