xu_NPAR08 - Artistic Thresholding Jie Xu Craig S Kaplan...

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Unformatted text preview: Artistic Thresholding Jie Xu Craig S. Kaplan * David R. Cheriton School of Computer Science University of Waterloo Figure 1: A photograph of St. Basil’s Cathedral in Moscow, rendered three different ways using artistic thresholding. Photograph used with permission from CNET Networks, Inc., Copyright 2008. All rights reserved. Abstract We consider the problem of depicting continuous-tone images using only black and white. Traditional solutions to this problem include halftoning, which approximates tones, and line drawing, which ap- proximates edges. We introduce “artistic thresholding” as a tech- nique that attempts to depict forms in an image. We apply seg- mentation to a source image and construct a planar subdivision that captures segment connectivity. Our artistic thresholding algorithm is a combinatorial optimization over this graph. The optimization is controlled by parameters that can be tuned to achieve different artistic styles. CR Categories: I.3.5 [Computer graphics]: Computational geometry and object modeling—Modeling packages J.5 [Arts and Humanities]—Fine arts G.2.2 [Discrete mathematics]: Graph theory—Graph algorithms Keywords: Thresholding, Halftoning, Black and white, Segmen- tation, Region adjacency graph 1 Introduction There are many algorithms for creating black and white represen- tations of continuous-tone images. The majority of these algo- rithms are concerned with halftoning , the approximation of con- tinuous tone using a distribution of black primitives on a white background [Ulichney 1987]. Halftoning was—and continues to * e-mail: { jiexu,csk } @cgl.uwaterloo.ca be—a necessary means of overcoming limitations in output tech- nologies. For the most part, computer displays have moved be- yond the need for extensive halftoning, but print technology is still highly dependent on it. Halftoning has also found its way into non-photorealistic rendering research; examples include algo- rithms for approximating tone with stipples [Deussen et al. 2000; Secord 2002], screens [Ostromoukhov and Hersch 1995], pen strokes [Winkenbach and Salesin 1994], or the walls of a maze [Xu and Kaplan 2007]. However, halftoning need not be the only way create a black and white depiction of an image. There exists a great deal of traditional art in black and white that makes no attempt at halftoning. An immediate example is line drawing (see Figure 2(a)), which seeks to convey all information about form and texture from a few sparse visual cues embedded in contours. Aesthetically, we appreciate the “efficiency” of this encoding of a scene, and enjoy the experience of unpacking it. Other traditional techniques use large regions of black and white in- stead of lines. Examples are shown in Figure 2. Some ink paintings use large black forms to carry all the salience of an image [Zheng 2000]. Papercutting, by its nature a binary medium, depicts an im- age by cutting holes in black paper [Xu et al. 2007]. Closely re- lated is stencilling, as in the graffiti work of the enigmatic British...
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This note was uploaded on 05/20/2011 for the course CAP 6701 taught by Professor Staff during the Spring '08 term at University of Florida.

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xu_NPAR08 - Artistic Thresholding Jie Xu Craig S Kaplan...

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