10: 5Stylized Line Drawing and Shading Effects

for Cartoon Rendering

Riyad Al-Rousanriyad@magicx.my

Mohd Shahrizal Sunarshahrizal@utm.my

Hoshang Kolivandkolivand@magicx.my

Hasan Alhajhamadhzhamad@magicx.my

MaGIC-X (Media and Games Innovation Centre of Excellence ) UTM-IRDA Digital MediaCentre Universiti Teknologi Malaysia 81310 Skudai Johor MALAYSIA

Abstract-Due to Increasing demands of cartoonstyle In many areas of computer graphic aspects, thispaper presents a simple stylized shading technique toenhance the cartoonlsh appearance In two aspects.First, a new toon-illumlnation model Is developed toemphasize the boundaries between diffuse reflectionpart and specular reflection part in the phongillumination model. The new discrete shading will beexploited to convey the light and dark orientations onthe surface of 3D model. Second, we combine stylizedlines with non-photorealistic shading effect to conveymore visual cues of tone. The experimental resultreveals the ability of proposed model to producemany cartoon effects.

Keywords - Non-photorealistic Rendering; LineDrwaing; Cartoon Rendering; Phong

1. INTRODUCTION

Non-Photorealistic Rendering is a branch ofcomputer graphics which concentrate on thealgorithms that generate images in a diversity ofartistic and illustrative styles [I] . Historically,producing images which are indistinguishable fromthe original is the main area of computer graphics[2]. In many cases the photorealistic is not theoptimal solution for rendering the scene. In contrast,Non-Photorealistic image is important forconveying the information and adding the simplicityof complex objects. NPR images distinguished overphotographs in many practical advantages such aslack of dispersion (e.g. in scientific illustration),focusing and clarification of essential details (e.g.,in maps, caricature and technical illustrations) [3],[4].

Several methods exist to produce correctphysically based shading, which are appropriate tocovey the 3D model in realistic styles [5],[6].However, for artistic purpose it is often to place thelighting sources in fictive positions as well asmodifying the light direction or altering the lightvertex to achieve the desired result. In this paper,we therefore present a new technique to enhance thecartoonish style appearance .

Toon-shading is a type of non-photorealisticrendering techniques developed in order to producecomputer graphics output appear to be hand-drawn[7]. It often used to convey the cartoon-style atmovies, video games and comic books . The

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intuitive end result of toon-shading is verysimplistic and exaggerative 2D animation. The mainfeature of toon-shading is the hard edge thatseparates between the shadowed and illuminatedcolors on the surface of 3D model as well as hardedge that separates the highlighting cue from themain material color. Fig. 1 depicts these cartoonishfeatures.

II . RELATED WORK

Because of the wide range of related work in thearea of non-photorealistic rendering, this sectioncovers the substantial body of the following twocategories: non-photorealistic lighting models andstylized line drawing.

Gooch et al. [8] was a pioneer in introducing anon-photorealistic lighting model for technicalillustration based on adding two tone-colors (warmcolor and cool color) to convey the perceptiondepth of the object. In [9], a new shading techniquebased on modifying the light diction according tosurface geometry features is proposed. It enhancedthe comprehension of complicated model details. Insame context, Rusinkiewicz et al. [10] introduced anon-photorealistic shading model based adjustingthe light position according to the smoothednormals. It applied multi-scale of shading toconvey details of the underlying model at allfrequencies.

In context of cartoon rendering, Lake et al. [7]proposed a very efficient real-time cartoon methodto render cartoon style. It based on the hard shadingtechnique that relies on mapping one dimensionaltexture. Barla et al. [II] extended one dimensionaltexture to two dimensional textures in order tosupport view-dependent effects, such as depthperception and abstractions levels. Severaltechniques exploited this approach to convey morevisual features such as visual saliency [12] andmaterial depiction (13].

In order to provide users more ability to controlthe stylized shape appearance over 3D model,several techniques have been proposed that modifythe shade effect. One of the works that the attentionin this context was [14]. They proposed a method tomanipulate the highlight shape in stylizedappearance. In [15] a new method to modifystylized light and shade is proposed, It allows