Research on Application of Computer Technology in Design of Traditional Woks of

Abstract. On the basis of long-term creative practice on traditional woks of art in China and takes ink painting as the representative of traditional woks of art, to make scientific analysis on painting medium and interaction relationship of ink painting and to summarize the painting mechanism of ink painting. And simulation algorithms of the present various artistic effect which are adopted are taken as reference and studied. Constructive objectives of Chinese painting simulation system are proposed，and functional and non-functional requirements encountered in the use of the process are analyzed for explaining application problems of computer technology in design and simulation of traditional woks of art.

Key words: computer technology, traditional woks of art, design and simulation, application

Introduction

Traditional woks of art in China has a long history, for example, traditional ink painting in China not only has the painting style of simplicity, abstraction and suggestions and has unique and distinctive characteristics, but also affects Japan, Korea and Southeast Asia and establishes its own system in the East as well as the world, which can be said to be the symbol of the Oriental art and the treasure of Chinese culture. Simulation on traditional woks of art is an intersectional research which combines computer science and art. With the rapid development of computer graphics, people have achieved great achievements on the simulation of traditional ink painting, especially Western painting including oil painting and watercolors, but simulation study on ink painting in China is still at an early stage now. Flexible strokes, abundant ink, repeated and overlapping water halo ink dyed of ink painting in China forms black-and-white construction with a unique art charm on paper. The render of texture method is completely different from other painting varieties, which has unique charm and artistic conception. Although the existing simulation ideas of Western Painting can be used as reference in some respects, the research of ink painting is unable to be introduced directly because its artistic effect caters to artistic characteristics of Western painting. Therefore, simulation study on ink painting has profound significance both in science and on the artistic aspect.

Requirements and Architecture Design on Simulation System for Ink Painting

Requirements of Simulation System for Ink Painting

Functional requirements of Usability involved in simulation systems of ink painting

(1) Document image processing function. The system can supports several formats and is convenient to import and export. In addition, it can save or save-as several common image formats such as bmp, jpeg and png, which makes it have better compatibility with other mainstream image processing software.

(2) Image editing function. Image editing function is the largest advantage of applying computers to simulate ink painting and is something that practical painting is not able to do. For example, rollover and pressing of mouse takes strokes as operands, the painter can restore a series of unsatisfactory strokes, and there is no need to worry about a momentary carelessness destroying the whole works, which makes their strokes bolder. Single stroke can be judged as follows. The time when the system detects that brush has contacted with paper by input device is the beginning of a stroke, and the time when the system detects that brush has left the paper is the end of a stroke. Meanwhile, the system also supports the function of shearing, copy, paste, clearing, erasure, zooming, selection and movement.

(3) Supporting different painting modes. The system resembles real ink painting, print content of brushes may fade gradually with the process of painting. However, in some cases, the user wants to use the same ink color for continuous creation which is the unique function of computer graphics. Therefore, the system should support at least 2 modes, that is, ink declining and ink constant.

(4) Supporting pen. The user should configure WACOM tablet and pen to apply the system. The support of pen makes the user could get a real feel for using electronic brush to paint. The movement of pen can control the track of strokes at the same time. The variation of stylus pressure not only can control the image of the pen to expand or contract appropriately, but also can change grey level and transparency alpha value of brush. Stylus tilt can simulate various artistic effect including diffusion, malapropism and center, and simplify painting process.

Architecture Design for Simulation System for Ink Painting

In order to carry forward the quintessence of Chinese culture and make the creation of ink painting more convenient and easy to use, taking research of 2D brush model as the basis and synthesizing the simulation results achieved in painting simulation research on imitation, single pen diffusion and overlay of muti pen is for the development on simulation drawing system of ink painting. The system has good interaction, and the user uses pan to paint in tablet and can draw the work of art with ink painting charm relaxedly on virtual paper with the difference of brush position and pressure.

(1)Development environment. Tablet, the system adopts the products of Intuos series in WACOM corporation and configures a pressure pen matching with tablet. Intuos is a tool which is designed by professional designer, it can realize the working ability of 1024 grade pressure, reading the precision of 0.1 mm. The tablet connect with the computers in USB interface. CPU, the CPU which is applied in developing the system is Intel Core2 dual core processor. Because the instantaneity of arithmetical operation and rendering has higher demands, operational capability cannot be too slow basically. Display, the display which is applied in developing the system is Onda 9600GT. Memory, 2G, DDR4000.

(2)Development tool. The development tool of the system is VC++7.0 , and Intel Imace Processing Library (IPL) is introduced to be as an auxiliary class library for accomplishing abundant image processing functions including copy, paste, zoom, revolution and blur.

(3) System Structure. The structure of the system is displayed in Figure 1.

Design and Realization of Simulation System for Ink Painting

Simulation study on ink painting in China is a subject with challenges in Computer Art field. This chapter mainly describes the design and realization of simulation system for ink painting through the previous architecture design on simulation system for ink painting. According to gradual research mode, the content of this paper put real and physical model of brush aside, establishes 2D brush model on the basis of experience, and makes digitizing and structuring process, which makes the user generates typical artistic effect of interactivity and structuring by using the input device such as mouse, keyboard and electronic brush, The experimental results show that the method can realize the simulation on ink painting more successfully.

Brush Model

Real brush consists of bush hair, and each brush hair has its own parameter information including position, color and ink level. In the process of creating ink painting, the painters can make the operations such as raising and pressing with the demans on different artistic effect and their own strokes. We find that changing the pressure value of brush can make two kinds of different effect by studying the response of real brush behaviour on pressure.

System Structure of Brush Model

System chart of brush behaviour simulation model is shown in Figure2, and is completed with 2 basic procedures. Firstly, data structure of initial brush is processed before putting brush to paper according to the established artistic effect. Secondly, after putting brush to paper, in the process of brushwork, controlling track of the brush and drawing up smooth curve with ink charm can realize interactivity and mobility of the system.

Realization of Simulation on Basic Strokes

The controlment on levels of initial brush means that the user set the channels of levels change and the range of levels adjustment and adjust the color of the channel.

Contrast effect of light ink,, dark ink and thick ink of the initial brush model after the process of using the method is shown in Figure 3.

In order to obtain transparency display of the edge for brush, we hope that the effect of transparency decreasing step by step from the edge of the initial brush to the internal, so we use gray level as the mark to find the edge step by step. When the edge is found out, its alpha value should be changed, these pixels should be added to background pixel and gray mark is kept using for seeking for the edge of next layer. The range of alpha value and layer straight inputted by the user has direct influence on transparency display of the edge for brush.

The following is pseudo-code description of algorithms:

Proc Transparence(low,high,Grade)

Compute-iStep{}: calculating variation of each level

GrayScale(): making gray mark

Bin(): binarization mark for locating the margin of brush

For(int i=0:I

If(i==1) The part beyond the margin of brush is set as total transparency on the second time

Border(istep*i): Finding the boundary with mark to change the transparency End for

End proc

Figure 4 is the effect of starting the stroke and finishing the stroke realized by the simulation of interactive system. But the change of strokes is not only confined to starting and finishing the stroke, controlling input device in the process of stroke can change brush structure parameter to alternate the stroke weight. And the user have already realized interactively the simulation of common artistic effect of ink .

Realization of Side-feng Effect

Side-feng is an important technique of writing for ink painting. The penholder inclines and the nib works on one side of ink line. Side-feng ink changes a lot and is different common styles in the integration of dark ink and light ink and in the combination of colors. The realization of side-feng effect can be divided into two processes, the initial side-feng stroke and side-feng movement track formed with rotation algorithm in real time.

Input device can't apply side-feng to paint after pressing like brush. In order to simulate the special effect of side-feng, firstly, we use the method of transparency or color changing gradually to initialize the brush structure and it is used in gradual and smooth change of transparency or color for pixel between two points specified by the user, which makes gradient in effect from one side of brush to another side. PtInit is the initial point and ptEnd is the end point, and the gradient in direction is from ptInit to ptEnd and the initial segment is from ptInit to ptEnd, which can make us ensure that scope of creeping 0 follows the gradient direction which is show in the shaded part. The translation of several vertical lines including AB and CD of gradient direction is used to realize gradual increase of transparency or color in gradient area, the calculation of transparency or color in each layer is also based on linear mapping method. The mapping range changes with different ranges of transparency or color and different selections on initial point and end point for the user. Figure 4 is the side-feng brush generated with the method, and it is easy to see the richness of variety in side-feng ink color of the figure.

Render Based on Texture Synthesis

Texture synthesis is an important technique for ink painting, which renders most of the internal texture of rocks. Typical method includes Phi Ma effect, cross point effect, rain effect or horseshoe point, vertical point and lotus leaf effect.

Overview of Three-dimensional Virtual Brush Model

(1) Brush model proposed in the paper

It is necessary to simulate complicated motions of brush as for an interactive simulation system for painting. Firstly, the input device such as wacom and pen are used to collect the position in the process of brushwork of the user and input information including pressure and angle of Inclination for penholder. And optimization algorithm is added to avoid shaking and increase the stability of virtual brush. System structure of virtual brush in this paper is shown in Figure 5.

(2) Quality parameters influencing the performance of brush

① Basic geometrical parameter. It includes length of brush point , radius of penholder and density of brush hair.The thicker of the brush hair, the better absorptivity of brush on ink. ② Stiffness of brush hair. Stiffness means the brush with different quality of brush hair. Different degrees of bend and distortion can happen in the same stress situation, and the smaller stiffness, the more easy for distortion. We use overall hardness value to describe the property of the brush model. ③ Plasticity of brush. Plasticity means that the brush bending with stress released suddenly. When the stress is releasing, it is not easy to return to the original state. Plasticity is the opposite of elasticity. ④ Friction coefficient. Friction coefficient of contact surface for brush and rice paper also has great influence on the final painting effect.

Geometric Model of Brush

Geometric representation of brush has close relationship with dynamic model, that is, a reasonable and effective geometric model not only can simplify calculation, but also can describe completely various movement and deformation of brush. We apply hierarchical structure of brush skeleton and brush surface.

(1) Construction of brush skeleton

If there is a skeleton among brush clusters, it is called spine, as shown in Figure 6. N key points distribute from brush foot to brush point for spine, and the spine is divided into several lengths which reduces gradually and N-1 sequential segments which are interconnected.

(2) Generation of brush surface

Brush surface has no influence on the final painting effect, and subdivision surface is used to be as geometric representation of brush point to draw the surface with the method of triangular griddingveneer. The so called triangular approach method is that any curved surface of the space is made of the segmented angle planes, which achieves the effect of approximate simulation, as shown in Figure 6.

Dynamic Simulation of Brush

(1) Sampling and processing of virtual brush

① Sampler Info is optimized, and the noise is eliminated with classic kalman filtering algorithm. ② Considering inertia factors.

If sampling data is Scant= (x, y, p, a . P )> (x, y) at a given time t , it expresses two dimension coordinate of brush on rice paper, p means pressure and (a. P) shows vergence direction of brush holder. So the status of virtual brush at a given time t.

(2) Dynamic regulation on brush skeleton

Deformation process of brush skeleton applies non-linear global deformation method based on the transformation ideas of Baal, that is, using a transformational parameter symbol to represent acting on the position function which needs to transform objects. Baa uses the following formula definition for transformation:

（X,Y,Z）=F(x,y,z)

(x, y,z) is the vertex position of objects before transformation, and (X,Y,Z) is the vertex position of objects after transformation. Non-linear global deformation method and empirical formula are combined to determine spatial position of key points in corresponding input conditions after transformation. The variety of brush transformation has been introduced in the fist chapter, it mainly includes bend, twist, diverge and combined deformation. The following is a detailed real-time simulation method of bend and torsional deflection.

① Bending deformation

Supposing bending zone along z-axis is (zmin

zmin,z＜zmin

z' z,zmin≤z≤zmax

zmax,z＞zmax

cos (x-k)+k,zmin≤z≤zmax

x= cos (x-k)+k+sin (z-zmin),z＜zmin

cos (x-k)+k+sin (z-zmax), z＞zmax

- sin (x-k)-z0,zmin≤z≤zmax

z - sin (x-k)-z0+ cos (z-zmin), z＜zmin

- sin (x-k)-z0+ sin (z-zmax), z＞zmax

Space transform on the above formula can make bending transformation along any space angle of brush holder. Fixing center of flexure z0, radius of curvature k and bending zone( zmin , zmax ) can be in accordance with empirical formula. The identification of center of flexure has relations with pressure level, swiftness of brush hair and inclination angle of brush holder. The more the pressure, the smaller the Stiffness and the smaller of intersection angle p between brush holder and XY plane, the more near of the center of flexure to brush root, bending area expands gradually and radius of curvature increases gradually.

② Torsional deformation

(X, Y,Z)=(xcos -ysin +ycos ,z) represents that brush moves around z axis through rotation transformation of zero angle. If the amount of rotation is allowed to be function of z, the object will be rotated, that is, B =f(z) function is used to transform, in which torsional rate of per unit length along z axis is formulated.

③ Bifurcation effect

The reason and process of appearing bifurcation is complicated, and it is set aside for the future research content of the paper because the limited time.

The above transformations are permutated and combined, brush surface is drawn in real time, and virtual brush can basically simulate all deformation process of real brush. The method avoids complicated mechanical stress model, which improves the operation efficiency.

Transmission Scheme of Ink Based on 3D Brush Model

(1) Render of brushwork

The point set of contact surface of brush and rice paper is curve fitted and the outline of unit stroke will be obtained. But brushwork is the brushwork outline formed by the contact of brush and paper at any moment and the collection of ink information for each point in outline.

(2) Draw of stroke

Stroke means the handwriting of brush on rice paper from pressing to raising. Two-dimensionimage deformation method based on substantive characteristics of polygons and vertex compensation method of simple polygons are applied to improve the drawing speed, vertex compensation is made between 2 transformations to make their vertexes equal. Supposing the vertices of the original polygons for two brushworks is respectively Vk and Vk+1, and the compensation formula is show as follows:

Vmax=max(Vk,VK-1)

Vm1n=min(Vk,VK-1)

Nls=(Vmax-1)mod(Vmax-1)

Np-(int)

(3) Two-way exchange of brush and paper

When the paper contacts with brush, if certain conditions are satisfied, both can exchange ink. Because the exchange of ink is finished through the exchange of water, there is a relation between water exchange capacity and ink exchange capacity, and the relation is set as k, the exchange formula is shown as follows:

Twarte=f(Wpaper,Wbrush)

Paper is the moisture content of paper cell at present, W brush is the moisture content of corresponding points for stroke, I paper is the ink content of aper cell at present and I brush is the ink content ofcorresponding points for stroke, and f represents transmission function of water.

(4) Drawing effect

Conclusions

The paper makes scientific introduction and analysis on drawing media of ink painting, reveals interaction relationship among painting materials including writing brushes, ink sticks, paper and inkstones, and summarizes the painting mechanism of ink painting. Sampling and processing of input information, controlment and deformation of brush model, and drawing output of the final stroke all refer to computer graphics, image processing and computer vision. The experiment results show that the system interface is good and the user can use pen to paint on the tablet. With different position ans pressure, the user can draw the works of art with ink charm relaxedly, which realizes the drawing of artistic effect for ink painting.

Acknowledgement

Foundation item: Provincial general supported by the "national area of university teaching material and local art research and development" (XJK011BJK007).

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