Wrinkle Rendering of Terrain Models in Chinese Landscape Painting_10.1.1.101

1238IEICE TRANS. INF. & SYST., VOL.E89–D, NO.3 MARCH 2006

PAPER

Wrinkle Rendering of Terrain Models in Chinese LandscapePainting

Der-Lor WAY†,††a) and Zen-Chung SHIH†, Nonmembers

SUMMARY Landscapes have been the main theme in Chinese paint-ing for over one thousand years. Chinese ink painting is a form of non-photorealistic rendering. Terrain is the major subject in Chinese landscapepainting, and surface wrinkles are important in conveying the orientation ofmountains and contributing to the atmosphere. Over the centuries, mastersof Chinese landscape painting have developed various kinds of wrinkles.This work develops a set of novel methods for rendering wrinkles in Chi-nese landscape painting. A three-dimensional terrain is drawn as an outlineand wrinkles, using information on the shape, shade and orientation of theterrain’s polygonal surface. The major contribution of this work lies in themodeling and implementation of six major types of wrinkles on the sur-face of terrain, using traditional Chinese brush techniques. Users can selecta style of wrinkle and input parameters to control the desired effect. Theproposed method then completes the painting process automatically.key words: non-photorealistic rendering (NPR), hatching, principle cur-vature direction, ts’un, texture stroke, Chinese landscape paintins

1. Introduction

During recent years, much research has addressed Westernpainting on Non-Photorealistic Rendering (NPR), includingwatercolors [3], [9], impressionistic painting [14], [20], pen-cil sketches [31], [32] and hatching strokes [7], [10], [15],[24], [30], [41]. These approaches deliver good results inwestern painting. However, these methods are inappropri-ate for Chinese ink painting. Chinese ink paintings typi-cally comprise a few simple strokes intended to convey theartist’s deep feelings regarding the painted object. Simulat-ing the style of Chinese landscape painting is challenging.The style includes free brush strokes, surface wrinkle andink diffusion on the paper [1], [8], [21].

One skill used in Western painting is using hatchingstrokes simultaneously to convey the type of material, tone,and form [7], [10], [15], [24], [30], [41]. Hatching describesgroups of strokes with a spatially coherent direction andquality. Stroke density controls the tone of the shading,while the character and arrangement of the strokes suggestsa surface texture. In pen-and-ink illustrations, variable-density hatching and complex hatch patterns convey shape,texture and lighting. Texture strokes called “ts’un” in Chi-

Manuscript received November 26, 2004.Manuscript revised June 25, 2005.†The authors are with the Department of Computer and Infor-

mation Science, National Chiao Tung University, 1001 Ta-HsuehRd, Hsinchu, Taiwan 30010, R.O.C.††The author is with the Graduate School of Arts and Tech-

nology, Taipei National University of Arts, 1, Hsuen-Yuen Road,Peitou, Taipei, 112, Taiwan, R.O.C.

a) E-mail: [email protected]: 10.1093/ietisy/e89–d.3.1238

nese. However, the represented material differs from thatrepresented by hatching. Texture strokes can be used to rep-resent a rough, cracked surface. Ts’un in Chinese landscapepainting is woven strokes that depict terrain textures. Themain goal of this work is to develop a set of novel methodsfor rendering terrain wrinkles (texture strokes) in Chineselandscape painting. A specific 3D terrain model is drawn inoutline and with texture strokes based on information on theshape, shade and orientation of the model surface.

The main contribution of this investigation is the mod-eling and implementation of six major texture strokes forterrain surface using traditional brush techniques in Chi-nese landscape painting. The proposed rendering tech-nique involves many fundamental parts, illustrated in Fig. 2.First, 3D terrain information is extracted to detect the edgesof the silhouettes, and to generate streamlines and ridgemeshes. The outline of a silhouette is then constructed andthe streamlines of the texture strokes are generated. All con-trol lines that involve the silhouette and streamlines then areprojected onto a 2D viewing plane. Brush strokes then areapplied to create an outline drawing and the texture of rockis captured using vertical or slanted strokes along the con-trol lines with a rich ink tone specified by a luminance map.Finally, the ink diffusion on the rice paper is simulated [12].

The rest of this paper is organized as follows. Section 2reviews works related to NPR. Section 3 then introducesthe properties of the six major texture strokes used in Chi-nese landscape painting. Subsequently, Sect. 4 describes theprocess of rendering texture strokes in detail. Next, Sect. 5shows the six different rendering styles of wrinkle. Section 6demonstrates the effectiveness of the method by presentingresults. Finally, Sect. 7 describes conclusions and suggestsareas for future research.

2. Related Works

In scientific and engineering applications, there is also aneed to abstract other form-defining cues from a grid Dig-ital Elevation Model (DEM). Visvalingam et al. [36]–[38]showed the possibility of automatically abstracting a typeof static 2.5D sketch called the profile-stroke (P-stroke)sketch. Lesage and Visvalingam [18] reviewed an image-based approach for deriving artistic sketches of terrain sur-faces. Lesage and Visvalingam used a 3D visualizationsystem for rendering luminance maps of different type ofterrain, and compared four common image-based edge de-tectors for extracting the sketches. Although Lesage and

Copyright c© 2006 The Institute of Electronics, Information and Communication Engineers

WAY and SHIH: WRINKLE RENDERING OF TERRAIN MODELS IN CHINESE LANDSCAPE PAINTING1239

(a) Hemp-fiber stroke (b) Axe-cut stroke (c) Lotus-leaf stroke

(d) Raindrop stroke (e) Mi-dot stroke (f) Boneless stroke

Fig. 1 Six main texture strokes examples in actual Chinese landscape paintings by Liu [13].

Visvalingam reproduced pen, pencil and charcoal sketchingstyles that can be obtained by adjusting the grey scale andthickness of output primitives, unfortunately these styles ofsketching differ from the properties of Chinese painting.

Expressive brush strokes are the first requirement inChinese landscape painting. Little research has addressedmethods for simulating brush stroke and ink behavior. Thebrush has been simulated as a collection of bristles thatevolve during a stroke. Strassmann [33] was the first toconsider a hairy brush as a 1D array of bristles. Lee [16],[17] considered elastic bristles that obey Hooke’s law anddescribed diffusion rendering of black ink paintings usingnew paper and ink models. Zhang et al. [44] presented a 2Dsimple cellular automaton-based simulation of ink behavior.Furthermore, Saito and Nakajima [28] devised a 3D physics-based brush model that enables users to paint various strokesintuitively and directly on a computer with a pen-like inputdevice. Xu et al. [42], [43] proposed a two-level hierarchi-cal geometry model. They used three B-spline curves tocontrol the three-dimensional brush geometry. Chu et al. [2]designed a 3D virtual brush model with ink depositing frombrush to paper in real time.

Sato et al. [29] extend their previous work to gener-ate sumi-e like paintings of arbitrary objects from three-dimensional polygonal models. Their proposed method re-alizes three brush stroke (Kou, Ten, and Shun) techniquesfor generating landscapes paintings. A Kou stroke is gen-erated for line drawing; a Ten stroke has the shape like agrain of rice, which is similar to dot stroke (Fig. 1 (d) and(e)); a Shun stroke has the shape like a hemp-fiber stroke(Fig. 1 (a)).

Our earlier work [39] modeled the effects of brushstrokes in traditional Chinese ink painting. That investiga-tion simulated two fundamental brush strokes, namely ver-

tical and slanted strokes. An interactive tool for paintingtwo rock textures (hemp-fiber and axe-cut) on a 2D imagewas also presented. Furthermore, a method [12] of simu-lating the diffusion of ink on rice paper was provided. Theproposed method was based on a physical mechanism andobservational model of the interaction among real drawingmaterials used in Chinese ink painting and of the variationin ink diffusion in the real world. The method can simulatevarious tone expressions on different paper types. The ef-fect of mixing strokes from different brush types was alsosimulated.

This work is also related to research on 3D non-photorealistic rendering, [4], [11], [13], [14] including styl-ized line illustrations, artistic hand-drawn illustrations andhatching painting styles. Many study have addressed theproblem of generating silhouettes and high-quality hatch-ing of static scenes. Markosian et al. [22] presented arandomized algorithm for locating silhouettes. Moreover,Winkenbach and Salesin [41] designed a method of render-ing smooth surfaces with pen-and-ink. Salisbury et al. [30]introduced prioritized stroke textures with tone values thatare mapped to the stroke arrangements, and presented im-pressive examples of computer-generated hatching. Fur-thermore, Sousa and Buchanan [31], [32] focused on thetechnical aspects of physically simulating real media, in-cluding pencil, crayon, blenders and erasers. Hertzmannand Zorin [10] generated high-quality silhouettes and estab-lished a scheme for placing image-space strokes for cross-hatching. Moreover, Lake et al. [15] described an interactivehatching system with stroke coherence in the image space.Finally, the method of Freudenberg [7] involved encoding astroke texture as a halftone pattern.

Surface rendering using principle curvature directionshas recently become an extremely popular technique for


non-photorealistic rendering. The most natural geomet-ric candidate is the pair of principal curvature directionfields [6], [35]. Rossl et al. [25]–[27] provided a new ap-proach for automatically generating a direction field for thestrokes. Discrete curvature analysis of such meshes permitsthe estimation of differential parameters. Curvature lines arethen constructed and used as strokes. This work also designsa simple weighted technique that uses a reference directiongenerating smooth direction fields on a surface, which aresuitable for generating streamlines for texture strokes of thesurface of a terrain.

3. Texture Strokes (Ts’un)

The Chinese ts’un depicts texture in Chinese painting. Ts’unrepresents a rough, cracked surface. Ts’un refers to wo-ven strokes that depict the texture of rocks. According to“The Mustard Seed Garden”, published in 1679, 19 texturestrokes were recognized by the time of the Ching Dynasty.These texture strokes are the most important elements ofChinese landscape painting.

Different kinds of texture strokes are used to representdifferent kinds of mountain. For example, granite moun-tains, which always appear as squares or pyramids, are al-ways painted using axe-cut strokes. Meanwhile, sedimen-tary mountains, which have a striated or layered texture,can be painted using hemp fiber strokes. Topographically,old flat lands are always painted using hemp-fiber strokes.When old lands rise up and are cut by rivers, they are treatedas new and may be painted using axe-cut strokes. Moreover,young land that is eroded by rain and rivers and becomessofter can be painted using hemp-fiber strokes and lotus-leafstrokes.

In the development of texture strokes in Chinese land-scape painting prior to the tenth century, the Chinese onlyused outlines to depict rocks and mountains, but they didnot yet use texture strokes. Within the outlines, ink shadingwas applied. Later artists attempted to substitute ink shad-ing for the texture strokes. Generally, texture strokes areapplied using six techniques. Figure 1 shows these six kindsof texture strokes painted by Liu [21].• Hemp-Fiber StrokeHemp-fiber stroke, shown in Fig. 1 (a), spreads and weaveslike the fibers of the hemp from which it takes its name.The hemp-fiber stroke is one of the most important strokesin Chinese landscape painting. Several texture strokes havebeen designed from the hemp-fiber strokes. The hemp-fiberstroke is a long line stroke painted with a dry vertical brush.Numerous long strokes are woven together in a pattern thatfrequently resembles a fishing net. This stroke imparts arich, profound and soft feeling and is best used for depictingrough rock surfaces.• Axe-Cut StrokeThe axe-cut stroke is a slanted stroke used in painting muchlike an axe is used to cut wood, shown in Fig. 1 (b). Theaxe-cut stroke is excellent for represent smooth cliffs andflat, planar rock surfaces. This stroke dominated South-

ern Sung landscape paintings between the 12th and 13thcenturies. Moreover, this stroke is ideal for depicting veryhard rock. The best-known exponents of the axe-cut strokesare Ma Yuan and Hsia Kwei, associated with the NorthernSchool of landscape painting, which thrived during the Sungdynasty.• Lotus-Leaf StrokeThe lotus-leaf stroke was named owing to its similarity tothe pattern of veins of lotus leaves, shown in Fig. 1 (c).These veins diverge and divide outwards from a central linemany times. The lotus leaf stroke is used to represent moun-tain ridges or cracks in rocks and is always painted using avertical brush.• Raindrop StrokeThis stroke, Fig. 1 (d), is named after the rain because it re-sembles a raindrop that has just reached the ground. Thisstroke is also known as the sesame stroke, the thorn strokeor the bean stroke. This stroke is applied particularly in theforeground of paintings including several broken fragmentsof rock. This stroke can be used to depict rocks that havebeen eroded, and thus have developed pockmarks and holes.•Mi-Dot StrokeMi-dot, Fig. 1 (e), is named after the artist who first used thiskind of dot, Mi Fei (1051–1107 A.D.). This dot is particu-larly good for portraying cloudy mountains and rainy land-scapes. This stroke is not only a texture stroke, but can alsobe used to depict a mountain forest containing several trees.These dots frequently appear horizontally, and therefore arealso called horizontal dots.• Boneless StrokeThe boneless stroke, Fig. 1 (f), is always painted with a wetbrush, using slanted strokes. The ink gradation is very softand differs from other texture strokes which have a strong,hard feeling. This stroke is not good for depicting the textureof rocks, but can successfully provide a three-dimensionalfeeling and give form and substance to rock. This stroke isgood present mountains are in the fog or in the mist.

4. Texture Stroke Construction

This section describes the rendering of texture strokes andthe use of the traditional brush technique to create primitivestrokes. Figure 2 illustrates the process of producing texturestrokes, which includes several basic elements:

(1) 3D information extraction: 3D terrain models renderedusing OpenGL include vertices, edges, faces and so on.The luminance map is specified as ink tone values.

(2) Control line construction: a direction field on the sur-face is computed, silhouette lines are detected andstreamlines in 3D object space are generated.

(3) Projection: all control lines, silhouette lines andstreamlines are projected onto a 2D viewing plane.

(4) Brush stroke: brush strokes are applied as outlinesin the drawing, and the texture strokes are vertical orslanted strokes [39] following streamlines using a richink tone specified by a luminance map.


Fig. 2 Surface wrinkle rendering diagram.

(5) Ink Diffusion: the motion of ink on rice paper is simu-lated [12].

Each part of the rendering diagram, shown in Fig. 2,builds upon the others and is crucial for developing texturestroke rendering methods. This work focuses on simulatingthe six main texture strokes and builds upon our previousworks [12], [39], [40]. Users can easily choose a style of tex-ture stroke and input parameters for controlling the desiredeffects. The proposed method then automatically completesthe painting process.

4.1 Extracting 3D Information

The Digital Elevation Model (DEM), also known as a gridfield, is a popular terrain file format in science and engineer-ing applications. All the terrain models presented here wereprovided by 3DEM Visualization Software [45]. Moreover,the grids of DEM heights were transformed into adjacenttriangles. The inputs of the 3D terrain polygonal modelswere rendered using OpenGL include vertices, edges andfaces. Moreover, the shading intensity was determined us-ing the luminance map. The gray-scaled image specifies theink tone values. All information can be extracted during thepre-process step without user intervention.

Fig. 3 The reference direction �Gref of a mesh F.

4.2 Drawing of Outlines

The outline, or silhouette, is the dominant feature of a shape.For polygonal meshes, a silhouette edge is defined as onethat connects front and back facing triangles. Visibility andadjacency then are determined based on a 2D projection ofthe silhouette edges. These edges are linked to create a longpath. Each brush stroke then is drawn in a style chosenby the user. These silhouette edges should be recalculatedwhenever the view changes. This work attempts to renderattractive silhouette outlines of 3D geometric shapes, usingbrush-strokes along well-chosen paths around each object.

4.3 Generation of Streamlines

A direction field on the surface should be chosen for stream-line generation. A natural geometric candidate is the pairof principal curvature direction fields [6], [35]. Ohtake etal. [23] presented adaptive smoothing tangential directionfields on a polygonal surface. Ohtake’s method effectivelysimulated pen-and-ink drawings of 3D objects. However,Chinese landscape painting seeks to simulate the surfacetexture of a terrain. The basic idea of generating streamlinesis adjusted for applying texture strokes.

Given a triangulated surface and the principal curvaturedirections at each vertex, the weighted averaging scheme re-peatedly and simultaneously updates each vertex directionby calculating the weighted sum of the directions. Selectingsuch a weight smooth the direction field and maintains thecoherence of the reference direction. The reference direc-tion is the gravity direction of the terrain. DEM is a gridfield of height, so for any vertex P (Px, Py, Pz), Py is theheight of the vertex. Figure 3 displays a triangular mesh Fwith normal vector �Fn. Moreover, �G denotes the directionof gravity (0,−1, 0). Let �Gref = �G + �Fn, where �Gref is theprojection of vector �G onto F. Finally, the vector t(P) isthe initial principal direction estimated at the vertices of themesh

t(P) =

t(P) +n∑

i=1

[Wi × t(Qi)]

/ 1 +

n∑i=1

Wi

,

Wi = (POi)

/ n∑

i=1

POi

,where Qi are all the neighboring vertices of P.


The vector t(F) is the streamline direction field com-bined with t(P1), t(P2), t(P3) and Gref on triangle F, t(F) =αGref + (1 − α)(t(P1) + t(P2) + t(P3)), where 0 < α < 1.Restated, if a raindrop were to fall on surface F, it wouldflow along the streamline direction t(F).

Once the streamline direction field is smoothed by thereference direction, a direction field t(F) is defined on theface of every triangle mesh. An initial point inside a trian-gle is selected, and the streamline is traced from the point,according to S k+1 = S k + ρt(Fk), where ρ is a real num-ber such that the line meets the edge of the triangle. More-over, S k+1 is located on the edge of the triangle. The tracingof the streamline ends when the streamline direction con-flicts with another streamline direction of the neighboringtriangle, as shown in Fig. 4, where the streamline stops ata ravine. Each triangle mesh can generate one streamline.Figure 5 (a) depicts the resulting stroke streamlines obtainedby this method.

The segments of S i are defined by segment(S i), whichis number of triangles through which S i passes. For exam-ple, segment(S ) is 9 in Fig. 4. The average of segment(S i)

of a terrain is defined by AVG(S ) =( n∑

i=1[segment (S i)]

)/n,

where n denotes the number of triangular meshes of aterrain. Normally, the number of iterations required forsmoothing is AVG(S ).

4.4 Ridge Mesh

The following steps are performed to determine whether amesh F is a ridge mesh of a terrain model. (1) Locate all the

Fig. 4 An example of streamlines generation.

(a) Streamlines without LOD (b) Streamlines with LOD (c) Streamlines from ridge mesh

Fig. 5 Examples of streamlines rendering with three different conditions.

streamlines; every triangle generates one streamline, whichdoes not stop until it meets the ravine; (2) Compute the num-ber of streamlines S total(Fi) that pass through the trianglemesh Fi; (3) specify a threshold S threshold: if the number ofstreamlines S total(Fi) � S threshold. Then, Fi is a ridge trian-gle mesh. Let Ridge(F) represent a set of triangle meshes,Ridge(F) = {S total(Fi) � S threshold; 0 � i < n, where n is thenumber of triangle meshes of a terrain}. Normally, the meshof the mountain peak only generates one passing stream-line (S total(Fpeak) � 1). Figure 5 (c) plots the streamlinesgenerated using ridge meshes. The ridge triangle mesh isextremely important for rendering lotus-leaf texture strokes.

4.5 Level of Detail

The level of detail (LOD) modeling method is an effectiveapproach for interactively visualizing complex terrain mod-els. When the terrain is so far away that it only occupiesone pixel, there is very little use in modeling the terrain inhigh detail. Figure 5 (a) plots all streamlines without LOD,the entire streamlines do not need to be displayed in sig-nificant detail because they may be obscured by a visiblepiece of the model, or be far enough away to make the de-tail meaningless. A large number of researchers have devel-oped algorithms for approximating terrains and other heightfields using polygonal meshes. Taylor and Barrett [34] ex-tract mesh approximations from rectangular quad-tree hier-archies. Both Lindstrom et al. [19] and Duchaineau et al. [5]define binary-tree hierarchies based on binary subdivisionof right isosceles triangles, and demonstrate real-time view-dependent LOD. In the proposed approach, the number ofstrokes to be shown is determined with the LOD. For eachinitial vertex Pi of streamline S i, Depth(Pi) represents thedepth value of Pi. Based on the Depth(Pi) value, look upthe hierarchical tree which streamline S i is selected or not.The streamlines are completely visible only when close tothe viewer. Figure 5 (b) depicts the stroke streamlines usingLOD. LOD is creating an impression of viewing distancewhen rendering terrain. The depth value also influences thewidth of the streamline brush stroke.

4.6 Brush Stroke of Streamlines

In order to generate brush strokes on the rice paper, the mod-els of the previous work are utilized [33], [39], [40]. In thissection, only explain the brush strokes of streamlines briefly.


The stroke of streamline is applied using a precise andflexible Cardinal spline. Cardinal spline is an interpolatedbut not approximated curve, which passes through all thespecified control points. All points of one streamline can beselected as control points. Cardinal spline facilitates slack-ness control by adjusting parameter t, with a smaller t im-plying a slacker curve. Figure 6 illustrates the precision andflexibility of the Cardinal spline. The brush stroke line canbe either softened or hardened.

While painting the brush stroke line, painters generallyslow the brush movement and increase the brush pressure tocapture the verve of the rock [33]. The pressure P is variedfrom 0 to 1. P determines whether bristles touch the ricepaper and the amount of ink deposited. For each bristle bi,the pressure weight Wp is defined by,

Wp =

0, if

∣∣∣b′i−B∣∣∣

2·B ≥ P∣∣∣b′i−B

∣∣∣2·B·P

· (P−1)+1, if

∣∣∣b′i−B∣∣∣

2·B < P(1)

where b′i is the coordinate of bi in the contact region, andB is the long axis of the ellipse contact region. Accord-ing to Eq. (1), even the same bristle exhibits a different de-posited ink as P changes. Figure 7 illustrates different levelsof pressure yield different strokes when applied with Cardi-nal spline.

4.7 Frame Coherence

Frame coherence is an important issue in NPR related re-search. If stroke placement and style differ significantly be-tween two consecutive frames, coherency problems will re-sult. Since streamlines are constructed during a preprocessstep, the position of each streamline is fixed. Furthermore,stroke parameters such as the size of the brush, the numberof bristles, the decreasing rate of ink, water, and so on, arepreserved. When strokes are applied at each frame, each

Fig. 6 Cardinal curves with different t. (a) Hard rock’s contour (t = 0.2).(b) Soft rock’s contour (t = −0.5).

Fig. 7 (a) Pressure on turning points (P = 0.6). (b) Pressure on turningpoints (P = 0.8).

stroke is guaranteed to have the same position and strokeparameters.

5. Interactive Texture Rendering

This work has designed an interactive application base onthe surface wrinkle rendering diagram (Fig. 2). This systemhas two editing modes: brush model and texture rendering.In each case, we provide an interface for direct user control,and rendering algorithms to support the required interactiv-ity.

Our previous work provided a brush model that en-ables a user to paint the Chinese brush simulation with initialconditions. There are slider controls to adjust the physicalparameters for the brush (ink decreasing, ink soaking vari-ation, bristle material, bristle dry-out, wet effect, and inkblending). The details of brush model are described in [39],[40]. The luminance map is a reference shading image forink tone during ink diffusion.

When loading the terrain model, there are many 3Dinformation need to extract before texture rendering (de-scribed in Sect. 5.1). Furthermore, the user selects one of thesix texture styles and input parameters to control the desiredeffect (described in Sect. 5.2). Users can to adjust strokelength, width, density, and level of detail (LOD) through theconventional user interface. The proposed method then au-tomatically completes the painting process. When the sys-tem renders the scene from a new perspective, it adapts thenumber and placement of the texture strokes as appropriateto maintain the textural consistency of the terrain.

5.1 Main Procedure

The main simulation procedure involves two phases: 3D in-formation extraction and texture rendering. When loadingthe terrain model, the first significant task FindNeighbor() isdetermining the neighborhood relation of the faces and ver-tices. Based on the proposed methods described in Sect. 4,PrincipalCurvature() computes the pair of principal curva-ture direction fields, GenerateStreamLines() generates thestreamline for each triangular mesh, FindRidge() identifiesthe all ridge meshes and CreateLODtree() establishes thehierarchical tree for the level of detail. During the texturerendering phase the user selects a texture style and input pa-rameters for controlling the desired effect.

Proc Extract3DInformation(Terrainfilename)FindNeighbor();// find the neighborhood relation of the

face and vertex.

// calculate the pair of principal curvature direction

fields.

PrincipalCurvature();

// generate streamline for each triangular mesh.

GenerateStreamLines();

// find the all ridge meshes.

FindRidge();

//create the hierarchical tree for the level of detail.

CreateLODtree();

end Proc


Proc TextureRendering()switch (Rendeing Type){case HEMP FIBER: HempFiberStroke();case AXE CUT: AxeCutStroke();

case LOTUS LEAF: LotusLeafStroke();case RAIN DROP: RainDropStroke();

case MI DOT: MiDotStroke();

case BONELESS: BonelessStroke();

}end Proc

5.2 Six Rendering Styles

5.2.1 Hemp-Fiber Stroke

Streamlines can be generated using the above method forrepresenting various rock surfaces. When hemp-fiber tex-ture strokes are applied, each streamline is projected onto a2D viewing plane and represented using the Cardinal splineto form one stroke path. If the streamline is visible and se-lected by LOD (w > 0), then paint it using vertical brushstroke with width w. To create a natural effect, stroke pertur-bation should be considered as another parameter by movingthe control points. Figure 8 (b) illustrates Angel Island inSan Francisco Bay as represented using hemp-fiber strokes.

Proc HempFiberStroke()for each streamline S[i]{w=LODtree(S[i]); //w is the width of stroke

if (w>0 and S[i] is Visible)BrushStroke(CardinalSpline(S[i]), Vertical, w);

}end Proc

(a) Angel Island.(polygonal model)

(c) Mount Olympus, USA.(polygonal model)

(e) the Grand Canyon.(polygonal model)

(b) Hemp-fiber stroke. (d) Lotus-leaf stroke. (f) Axe-cut stroke.

Fig. 8 Examples of Hemp-fiber, Lotus-leaf and Axe-cut strokes in shaded area.

5.2.2 Lotus-Leaf Stroke

To draw the lotus-leaf stroke, this study only selected thestreamlines that were generated by a ridge triangle mesh.The edge of the ridge forms the veins of the lotus leaf. Theother steps are same as for a hemp-fiber stroke. Figure 8 (c)illustrates Mount Olympus, Washington, and Fig. 8 (d) illus-trates the simulated result obtained by applying lotus-leaftexture strokes.

Proc LotusLeafStroke ()for each streamline S[i]{w=LODtree(S[i]); //w is the width of the stroke

if (w>0 and S[i] is Visible and S[i] is Ridge)//using vertical stroke

BrushStroke(CardinalSpline(S[i]), Vertical, w);

}end Proc

5.2.3 Axe-Cut Stroke

The axe-cut stroke is a slanted stroke. An artist slants thebrush so that the brush tip bends slightly sideways. Nor-mally, the stroke has a rectangular or triangular shape. Theprocess of applying an axe-cut texture stroke is the same asfor applying the hemp-fiber stroke. The only difference isthe application of the slanted brush stroke along the stream-lines. Figure 8 (f) illustrates the Grand Canyon as repre-sented using axe-cut strokes.

Proc AxeCutStroke ()for each streamline S[i]{w=LODtree(S[i]); //w is the width of the stroke


(a) Mountain (polygonal model) (b) Raindrop stroke (c) Mi dots stroke

Fig. 9 Examples of Raindrop and Mi-Dot strokes in shaded area.

if (w>0 and S[i] is Visible)//using the slanted stroke

BrushStroke(CardinalSpline(S[i]), Slanted, w);

}end Proc

5.2.4 Raindrop Stroke and Mi-Dot Stroke

The dot texture strokes use the vertex of a streamline to re-place an edge. The position of the vertex is perturbed tocreate a natural effect. The dot size depends on the depthvalue and a random number. Figure 9 (a) plots the modelof a mountain and Fig. 9 (b) depicts the raindrop dot formedusing a wet brush. The Mi dots are applied using the vertexof the streamline of a lotus-leaf and a ridge vertex. A hori-zontal line then is created at each vertex. The length of eachhorizontal line also depends on the depth value and the dis-tance from the top ridge. Figure 9 (c) displays the simulatedresult obtained using a wet brush.

Proc RainDropStroke ()for each streamline S[i]{w=LODtree(S[i]); //w is the the stroke width

if (w>0 and S[i] is Visible) PaintDot(S[i], w);}

end Proc

Proc MiDotStroke ()foreach streamline S[i]{w=LODtree(S[i]); //w is the width of the stroke

if (w>0 and S[i] is Visible and S[i] is Ridge)PaintMiDot(S[i], w);

}end Proc

5.2.5 Boneless Stroke

As described in Sect. 3, in a boneless stroke, the ink is darkclose to the edge of the silhouette, and lightens with in-creasing distance from the edge. The proposed method forrepresenting the ink-gradient of a boneless stroke in manualpainting is as follows. First, the edges of the silhouette aredetermined. Second, the distance between a pixel and sil-houette pixel must be calculated. Third, a brush stroke withan ink tone dictated by distance is applied. Finally, the inkis diffused by the very wet brush.

(a) (b)

Fig. 10 An example of distance value between silhouette and boundary.

(a) 3D polygonal model

(b) Boneless stroke

Fig. 11 An example of the boneless stroke by our method.

In this work, silhouette edges are determined in a 3Dobject-space. However, the distance from each pixel to thesilhouette is determined in a 2D image space. Figure 10 (a)illustrates black silhouette lines. The color of the neighborpixel of the silhouette is white if the neighbor pixel is notprojected from the face of the same triangle or the neighbor-ing triangle. Restated, the white pixel is a boundary pixel.Moreover, Db is the minimum distance from a pixel to thesilhouette, and Dw is the minimum distance from a pixel tothe boundary, as shown in Fig. 10 (a). To normalize the dis-tance from zero to one, let D = Db/(Db+Dw). Figure 10 (b)displays the initial ink tone determined based on the distancevalue. Finally, the ink diffuses in a manner determined bythe distance value and foggy luminance map. Figure 11 (a)


depicts a terrain model and Fig. 11 (b) illustrates the resultof Fig. 11 (a) for boneless strokes.

6. Experimental Results

Figures 12 and 13 shows the result using numerous wrin-kles. Figure 13 (c) integrates wrinkles with tree-dots andwater wave lines. Figure 14 displays Angel Island as ren-dered in hemp-fiber strokes from various viewpoints.

Table 1 lists the performance measurements of the pro-posed methods. The first column refers to the figures, andthe second column contains the number of all of the poly-

(a) Streamlines.

(b) Hemp-fiber, lotus-leaf, axe-cut and boneless.

(c) Boneless stroke.

Fig. 12

Fig. 14 Hemp-fiber stroke of Angel Island in different viewpoint.

gons in a scene. Finally, the third column indicates the userspecified surface wrinkle type. The fourth column reflectsthe computation time of streamlines generation when theterrain is loaded. The fifth and sixth column shows therendering time under different conditions. The final twocolumns display the painting time for two image sizes. Thecomputational time of ink painting depends on the numberof visible streamlines to be drawn and the image size.

7. Conclusion and Future Works

This work developed a set of novel methods for renderingterrain wrinkles in Chinese landscape painting. A specific3D terrain model is presented in outline and with texturestrokes using information on the shape, shade and orienta-tion of the model surface. The major contribution of this

(a) Streamlines.

(b) Hemp-fiber, outline and boneless.

(c) Hemp-fiber, tree-dots and water’s wave line.

Fig. 13


Table 1 Performance measurements (sec).

work lies in the modeling and implementation of six ma-jor texture strokes for terrain surface using traditional brushtechniques in Chinese landscape painting. Users can easilychoose a style of texture strokes and input some parame-ters to control the desired effects. The proposed method un-derwrites the complete painting process automatically. Theproposed rendering technique involves many parts: 3D in-formation extraction; control line construction; projectiononto a 2D image; brush stroke application and ink diffusion.Effective results were also generated using the methods pre-sented here.

Future studies should address the following issues tobuild upon the ideas presented here.

1. This work focuses on six main texture strokes. Al-though these are the most common texture strokes inChinese landscape painting, many others should be de-veloped. Developing other strokes would not be diffi-cult since the concept of texture strokes closely resem-bles these six strokes.

2. Normally, Chinese landscape painting contains numer-ous objects, for example trees, rivers, lakes, clouds,boats, houses, and so on. Integrating with above ob-jects is an interesting and important task.

3. A few recent studies have addressed real-time render-ing. To date, ink diffusion remains a time consumingwork. How to render ink diffusion with real-time willbe a major future challenge.

Acknowledgement

The authors would like to thank the National Science Coun-cil of the Republic of China for financially supporting thisresearch under Contract No. NSC 94-2213-E-119-001.

References

[1] C.C. Chiu and C.C. Ying, Chinese Painting: A ComprehensiveGuide, Art Book Co., Ltd., 1997.

[2] S.H. Chu and C.L. Tai, “Real-time painting with an expressive vir-tual Chinese brush,” IEEE Comput. Graph. Appl., vol.24, no.5,pp.76–85, 2004.

[3] C.J. Curtis, S.D. Anderson, J.E. Seims, K.W. Fleischer, and D.H.Salesin, “Computer-generated watercolor,” Proc. SIGGRAPH 97,pp.421–430, 1997.

[4] D. DeCarlo, A. Finkelstein, S. Rusinkiewicz, and A. Santella, “Sug-gestive contours for conveying shape,” Proc. SIGGRAPH 2003,pp.848–855, 2003.

[5] M. Duchaineau, M. Wolinsky, D. Sigeti, M. Miller, C. Aldrich,and M. Mineev-Weinstein, “ROAMing terrain: Real-time optimallyadapting meshes,” Proc. Visualization ’97, IEEE, pp.81–88, 1997.

[6] G. Elberg, “Interactive line art rendering of freeform surfaces,”Comput. Graph. Forum, vol.18, no.3, pp.1–12, 1999.

[7] B. Freudenberg, “Real-time stroke textures” (Technical Sketch)SIGGRAPH 2001 Conference Abstracts and Applications, p.252,2001.

[8] L.M. Gao, Chinese Painting by Chang Da-Chien, Art Book Co.,Ltd., 1988.

[9] A. Hertzmann, “Painterly rendering with curved brush strokes ofmultiple sizes,” Proc. SIGGRAPH 98, pp.453–460, 1998.

[10] A. Hertzmann and D. Zorin, “Illustrating smooth surfaces,” Proc.SIGGRAPH 2000, pp.517–526, 2000.

[11] A. Hertzmann, “A survey of stroke-based rendering,” IEEE Comput.Graph. Appl., vol.3, no.4, pp.70–81, 2003.

[12] S.W. Huang, D.L. Way, and Z.C. Shih, “Physical-based model of inkdiffusion in Chinese paintings,” J. WSCG, vol.10, no.3, pp.520–527,2003.

[13] T. Isenberg, N. Halper, and T. Strothotte, “Stylized silhouettes at in-teractive rates: From silhouette edges to silhouette strokes,” Comput.Graph. Forum, vol.21, no.3, pp.249–258, 2002.

[14] R.D. Kalnins, L. Markosian, B.J. Meier, M.A. Kowalski, J.C. Lee,P.L. Davidson, M. Webb, J.F. Hughes, and A. Finkelstein, “WYSI-WYG NPR: Drawing strokes directly on 3D models,” Proc. SIG-GRAPH 2002, pp.755–762, 2002.

[15] A. Lake, C. Marshall, M. Harris, and M. Blackstein, “Stylizedrendering techniques for scalable real-time 3D animation,” Proc.NPAR2000, pp.13–20, 2000.

[16] J. Lee, “Simulating oriental black-ink painting,” IEEE Comput.Graph. Appl., vol.19, no.3, pp.74–81, 1999.

[17] J. Lee, “Diffusion rendering of black ink paintings using new paperand ink models,” Comput. Graph., vol.25, pp.295–308, 2001.

[18] P.L. Lesage and M. Visvalingam, “Towards sketch-based explorationof terrain,” Comput. Graph., vol.26, no.2, pp.309–328, 2002.


[19] P. Lindstrom, D. Koller, W. Ribarsky, L. Hodges, N. Faust, and G.Turner, “Real-time, continuous level of detail rendering of heightfields,” Proc. SIGGRAPH ’96, pp.109–118, 1996.

[20] P. Litwinowicz, “Processing images and video for an impressionisteffect,” Proc. SIGGRAPH 97, pp.407–414, 1997.

[21] Y. Liu, Ten Thousand Mountains, pp.56–73, Shui-Yun-Chai Studio,New York, 1984.

[22] L. Markosian, M.A. Kowalski, S.J. Trychin, L.D Bourdev, D.Goldstein, and J.F. Hughes, “Real-time nonphotorealistic render-ing,” Proc. SIGGRAPH 97, pp.415–420, 1997.

[23] Y. Ohtake, M. Horikawa, and A. Belyaev, “Adaptive smooth-ing tangential direction fields on polygonal surfaces,” IEEE Com-puter Graphics and Application, 2001 Proc. 9th Pacific Conference,pp.189–197, 2001.

[24] E. Praun, H. Hoppe, M. Webb, and A. Finkelstein, “A real-timehatching,” Proc. SIGGRAPH 2001, pp.579–584, 2001.

[25] C. Rossl, L. Kobbelt, and H. Seidel, “Line art rendering of triangu-lated surfaces using discrete lines of curvature,” Proc. WSCG 2000,pp.168–175, 2000.

[26] C. Rossl and L. Kobbelt, “Line art rendering of 3D-models,” Proc.Pacific Graphics 2000, Los Alamitos, pp.87–96, IEEE Computer So-ciety Press, 2000.

[27] C. Rossl and L. Kobbelt, “Approximation and visualization of dis-crete curvature on triangulated surfaces,” Proc. VMV 99, pp.339–346, 1999.

[28] S. Saito and M. Nakajima, “3D physics-based brush model for paint-ing,” Proc. SIGGRAPH 99: Conference Abstracts and Applications,p.226, 1999.

[29] Y. Sato, T. Fujimoto, K. Muraoka, and N. Chiba, “Storoke-basedsuibokuga-like rendering for three-dimensional geometric models –Ten and shun touches,” J. Society for Art and Science, vol.3, no.4,pp.224–234, 2004.

[30] M.P. Salisbury, M.T. Wong, J.F. Hughes, and D.H. Salesin, “Ori-entable textures for image-based pen-and-ink illustration,” Proc.SIGGRAPH 97, pp.401–406, 1997.

[31] M.C. Sousa and J.W. Buchanan, “Observational model of blendersand erasers in computer-generated pencil rendering,” Proc. GraphicsInterface ’99, pp.157–166, 1999.

[32] M.C. Sousa and J.W. Buchanan, “Computer-generated graphite pen-cil rendering of 3D polygonal models,” Comput. Graph. Forum,vol.18, no.3, pp.195–208, 1999.

[33] S. Strassmann, “Hairy brushes,” Proc. SIGGRAPH 86, pp.225–232,1986.

[34] D.C. Taylor and W.A. Barrett, “An algorithm for continuous resolu-tion polygonalizations of a discrete surface,” Proc. Graphics Inter-face ’94, pp.33–42, 1994.

[35] L. Victoria, “Interrante illustrating surface shape in volume data viaprincipal direction-driven 3D line integral convolution,” Proc. SIG-GRAPH 97, pp.109–116, 1997.

[36] M. Visvalingam and K. Dowson, “Towards cognitive evaluation ofcomputer-drawn sketches,” Vis. Comput., vol.17, no.4, pp.219–235,2001.

[37] M. Visvalingam and J.C. Whelan, “Occluding contours within artis-tic sketches of terrain,” Proc. 16th Conference of Eurographics-UK,pp.281–289, March 1998.

[38] M. Visvalingam and K. Dowson, “Algorithms for sketching sur-faces,” Comput. Graph., vol.22, no.2/3, pp.269–280, 1998.

[39] D.L. Way and Z.C. Shih, “The synthesis of rock textures in Chineselandscape painting,” Comput. Graph. Forum, vol.20, no.3, pp.C123–C131, 2001.

[40] D.L. Way, Y.R. Lin, and Z.C. Shih, “The synthesis of trees in Chi-nese landscape painting using silhouette and texture strokes,” J.WSCG, vol.10, no.3, pp.499–507, 2002.

[41] G. Winkenbach and D.H. Salesin, “Rendering parametric surfacesin pen and ink,” Proc. SIGGRAPH 96, pp.469–476, 1996.

[42] S. Xu, C.M. Lau, F. Tang, and Y. Pan, “Advanced design for a realis-tic virtual brush,” Comput. Graph. Forum, vol.22, no.3, pp.533–542,

2003.[43] S. Xu, M. Tang, F.C.M. Lau, and Y. Pan, “A solid model based vir-

tual hairy brush,” Comput. Graph. Forum, vol.21, no.3, pp.299–308,Sept. 2002.

[44] Q. Zhang, Y. Sato, J. Takahashi, K. Muraoka, and N. Chiba, “Sim-ple cellular automaton-based simulation of ink behaviour and its ap-plication to suibokuga-like 3D rendering of trees,” J. Vis. Comput.Animation, vol.10, pp.27–37, 1999.

[45] 3DEM Software http://www.visualizationsoftware.com.

Der-Lor Way received the B.S. degreein computer science from Soochow Universityin 1986, MS degree in computer science fromChung-Yuan Christian University in 1988. Hestayed in Communications and Computer Labo-ratory (CCL) to research multimedia and virtualreality for 11 years. He is currently a teacher inthe Taipei National University of Arts. He alsois a Ph.D. candidate in the Department of Com-puter and Information Science at National ChiaoTung University, Taiwan. His research interests

are in the area of non-photorealistic rendering and virtual reality.

Zen-Chung Shih received the B.S. degreein Computer Science from Chung-Yuan Chris-tian University in 1980, MS degree in 1982 andPh.D. degree in 1985 in computer science fromthe National Tsing Hua University. Currently,he is a professor in the Department of Computerand Information Science at the National ChiaoTung University in Hsinchu. His current re-search interests include procedural texture syn-thesis, non-photorealistic rendering, global illu-mination, and virtual reality.

Wrinkle Rendering of Terrain Models in Chinese Landscape Painting_10.1.1.101

Documents

Transcript of Wrinkle Rendering of Terrain Models in Chinese Landscape Painting_10.1.1.101