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Part of the difficulty in depicting stylized materials stems from the fact that the techniques artists use to draw materials are based on accumulated artistic knowledge. These guidelines they use to dehal-00828067,

Figure 1: We describe Vector Shade Trees that represent stylized materials as a combination of basic shade nodes composed of vector graphics primitives (a). Combining these nodes allows the depiction of a variety of materials while preserving traditional vector drawing style and practice. We integrate our vector shade trees in a vector drawing tool that allows users to apply stylized shading effects on vector line drawings (b,c). This pdf contains png versions of vector art to avoid viewer compatibility problems; full vector versions of our results are in supplemental material. Original line drawing from koconmus, openclipart.org c, colored version c the authors. Vector graphics represent images with compact, editable and scalable primitives. Skillful vector artists employ these primitives to produce vivid depictions of material appearance and lighting. However, such stylized imagery often requires building complex multilayered combinations of colored fills and gradient meshes. We facilitate this task by introducing vector shade trees that bring to vector graphics the flexibility of modular shading representations as known in the 3D rendering community. In contrast to traditional shade trees that combine pixel and vertex shaders, our shade nodes encapsulate the creation and blending of vector primitives that vector artists routinely use. We propose a set of basic shade nodes that we design to respect the traditional guidelines on material depiction described in drawing books and tutorials. We integrate our representation as an Adobe Illustrator plug-in that allows even inexperienced users to take a line drawing, apply a few clicks and obtain a fully colored illustration. More experienced artists can easily refine the illustration, adding more details and visual features, while using all the vector drawing tools they are already familiar with. We demonstrate the power of our representation by quickly generating illustrations of complex objects and materials.

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(c) Editing result(b) Multi-layer vector representation(a) Input photograph Figure 1: Our interactive vectorisation technique lets users vectorise an input bitmap (a) into a stack of opaque and semi-trans-parent vector layers composed of linear or radial colour gradients (b). Users can manipulate the resulting layers using standard tools to quickly produce new looks (c). We outline semi-transparent layers for visualisation; these edges are not part of our result. We rasterised figures to avoid problems with transparency in some PDF viewers. See supplemental material for vector graphics. We present an interactive approach for decompositing bitmap drawings and studio photographs into opaque and semi-transparent vector layers. Semi-transparent layers are especially challenging to extract, since they require the inversion of the non-linear compositing equation. We make this problem tractable by exploiting the parametric nature of vector gradients, jointly separating and vectorising semi-transparent regions. Specifically, we constrain the foreground colours to vary according to linear or radial parametric gradients, restricting the number of unknowns and allowing our system to efficiently solve for an editable semi-transparent foreground. We propose a progressive workflow, where the user successively selects a semi-transparent or opaque region in the bitmap, which our algorithm separates as a foreground vector gradient and a background bitmap layer. The user can choose to decompose the background further or vectorise it as an opaque layer. The resulting layered vector representation allows a variety of edits, such as modifying the shape of highlights, adding texture to an object or changing its diffuse colour. 1.