Introduction to Computer Graphics

HCI 학술 대회

2000. 1.

중앙대학교 첨단영상 전문대학원교수 윤 경 현

Khyoon@cglab.cse.cau.ac.kr tel)820-5308

Introduction to Computer Graphics

What is C.G

Modeling

Rendering

Animation

New Technology

What is CG

Humans Communicate well with images

1/3 of our brain is devoted to visual processing

A picture is worth a thousand words

WYSIWYG paradigm

In the past, graphics was only used to convert

numerical data sets to graphs.

business graphs (bar chart, pie char

Nowdays, graphics is used to depict the complex data sets and

virtual /chaotic (natural) phenomena

VR, SV

What is CG

Definition : Picture style I/O technology involving the Creation manipulation storing and display of pictures with the aid of computer

Numericaldata

Picture (Image)data

input output

C.G vs I.P

Computer Graphics a computer is used to create a picture.

model based approach

concerns pictorial synthesis of real or imagery objects from

computer based model

deals with vector data

ex) Jurassic park, Game

Image Processing a computer is used to modify or interpret existing pictures.

processing of sensor based data

concerns scene analysis.

improving picture quality

machine perception of visual info

deals with pixel data

ex) Recognition of car license plate

Interpretation of satellite image

C.G vs I.P

Graphics Pipeline

Model & View Transform

Lighting & EyeMaterial

Projection

Clipping

ScreenMapping

Display

Modeling

Rendering Illumination model Texture mapping Ray Tracing

Shading

Translation, Rotation, Scaling Geometric Modeling Solid Modeling Procedural Modeling

Frame buffer, Z-buffer, Back buffer, double buffer

Modeling

대상물체의 형상화를 위해 사용되는 기술 General Object : Geometric Primitive

Using line, polygon, sphere, cubic Input : 형상화 물체의 3D coordinate Output : Wire framed objects Technique : Interpolation / Approximation, CGS, Sweeping, Deformation

Natural object : Proceduralism 에 의한 형상화 Input : natural object 의 growth rule Output : Wire framed objects Technique : Fractal, Grammar-based modeling, particle system, physically based modeling 등

Modeling Technique

Geometric Modeling Bezier, Spline, NURBS

Solid Modeling SOR, Sweeping, CSG

Advanced Modeling Technique Proceduralism

Grammar Based Modeling

Particle System

Fractal Modeling

Geometric Modeling

G.M. deals with the construction of smooth curves and surfaces by using polygon mesh

Bezier Surface

Solid Modeling

Representation of Volumes completely surrounded by surfaces.

Geometric Modeling : describe the boundary of objects Need to distinguish between inside or outside Also, be able to compute properties of object

ex) CAD, CAM application Deals with the construction of volumetric objects & its

operations.

Techniques SOR, Sweeping, CSG

Sweeping

Closed polygons and curves generates finite volume by sweeping transformation Rotation, Sweeping

SOR(Surface Of Revolution)

To generate a 3-D surface, revolve a two dimensional entity. e.g., a line or plane about the axis in space. called surfaces of revolution

CSG(Constructive Solid Geometry)

Combination rules for solids Each combines two solids

Union(+), Difference(-), Intersection (&) Results can be used as a new solid

CSG Tree

Fractal Modeling

B. Mandelbrot 에 의해 기본 개념 완성 .

Self-similarity 성질과 브라운 운동의 randomness 를 결합하여 모델링

Fractal Mountain

Grammar Based Modeling

자연물 모델링에 사용 ( 식물학자 Lindenmayer 에 의해서 제안 ) Prusinkiewicz 에 의해 발전됨 (L-system)

식물의 생성정보를 문법에 의해 반복 치환함으로써 모델링

Particle system (1/2)

1982 년 W.Reeves 에 의해 영화 ‘ Star Track’ 의 제작을 위해 고안해 냄 .

주로 작은 입자의 집합에 의한 물체 모델링에 의해 사용 Ex) 불 , 물 , 연기 , 구름 등

시간의 흐름에 따른 입자의 변화 ( 개수 , 방향등 ) 를 확률통계적으로 조절Initial velocitiesof several particles

Center of explosion systemParticle-creationregion

Ejection angle

Particle system (2/2)

Rendering

Process of photo-like image generation Rendering adds light to the model

The renderer tracks the light in the scene to determine how the scene looks to the viewer.

기 법 : Hidden elements Removal

Shading

Texture mapping

Ray-tracing

Radiosity

Volume Rendering

Hidden Surface Removal

3 차원 입체도형을 2 차원 화면에 display 하려고 할 때 도형 자체 혹은 다른 도형에 의해 가려지는 면을 제거

물체를 처리하는 방법에 따라 Object space method

Depth Sorting algorithm

Image space method Z-buffer algorithm

Scan-Line algorithm

Area-subdivision algorithm

Shading

Polygon 내부를 칠하는 방법으로 구분

Flat Shading Gouraud Shading Phong Shading

Texture Mapping (1/3)

Texture image

Flat Mapping Cylindrical/Spherical Mapping

2D texture image =>3D object : mapping method

Texture Mapping (2/3)

Bump Mapping Chrome/Reflection Mapping

Texture Mapping (3/3)

Refraction Mapping Environment Mapping

From Advanced animation and Rendering techniquesAlan watt, Mark watt

시선광선

Mipmap cube

교점

1 2 3 4

5

6

Ray Tracing(1/4)

Suggested by Appel in 1968 : called by ray casting process 관찰자의 눈에 들어오는 광선을 추적하여 광선의 색을 화면에 표시해

주는 방법 ray 의 방향 : eye light source

각 ray 를 추적하면서 simulation 많은 시간 소모 정반사에 중점을 둠 , 난반사 표현에는 한계

eyeray

screenrefraction

reflection

Ray Tracing(2/4)

Reflection/Refraction

Ray Tracing(3/4)

Backward Ray Tracing

Ray Tracing(4/4)

DOF, Motion Blur(Distributed Ray Tracing)

Radiosity (1/2)

Basic assumption conservation of radiation energy in a closed environment.

Energy is radiated uniformly in all directions.

Definition radiosity of surface

the rate at which radiation energy leaves a surface per unit area.

Basic method determine all light interactions(radiosities) in the environment.

Render the scene from any viewpoint

Radiosity (2/2)

열 전달 이론을 기반으로 조명의 영향을 시뮬레이션 부드러운 그림자나 자연스러운 색 번짐 효과

Volume Rendering (1/2)

Technique for visualizing volume primitive Have information inside if

Not consist of surface and edges at all

Be too voluminous to be represented geometrically

Volume Rendering & Surface Rendering

Direct projection Translucent gel Information inside objects Discrete Large data sets Slow Classification

Intermediate representation Tangible surface Information on surfaces Continuous Compact representation Fast Iso-surface

Volume Rendering (2/2)

Voxels

Polygons

Animation

Animation is giving variations on the model over time Different keys given by the animator are interpolated to give

in betweens.

2D Animation (Cell Animation)

3D Animation 기 법 : Key-frame Animation

Kinematics / Inverse Kinematics

Dynamics

Metamorphosis

Key-frame animation

Key-frame animation Animator specifies key attributes of 3D objects at particular moments

in the animation Position, Orientation, Color, Amouts of deformation, etc…

The system does inbetweening by interpolating the attributes

Keyframe animation

Kinematics & Dynamics

Kinematics & Dynamics Kinematic is that branch of physics which involves the description of

motion, without examining the forces which produce the motion

Dynamics involves an examination of both a description of motion and the forces which produce it

Metamorphosis

Metamorphosis Combine these two idea

Key frame animation + pixel based cross-dissolve

Morphing : A => B

Warping : A => A’

Morphing

New technology

IBR(Image Based Rendering) 3D geometric data reconstruction from images

NPR(Non-Photorealistic Rendering) A means of creating imagery that does not aspire to realism

IBR(Image Based Rendering)

3D model-based Rendering Explicit use of 3D models

Uses conventional rendering pipeline

Speed dependent on scene complexity

Relies on hardware accelerator for speed

Requires sophisticated software for realism

Image-based Rendering Directly uses collection of

image

Based on interpolation or pixel reprojection

Speed independent on scene complexity

Relies on processor speed

Realism depends on input images

IBR(Image Based Rendering)

Traditional Modeling and Rendering

Image based Modeling and Rendering

IBR(Image Based Rendering)

NPR(Non-Photorealistic Rendering)

A means of creating imagery that does not aspire to realism

Researchers attempt to widen the range of rendering output possibility beyond photo-realism

Generate imagery that looks like that made by artists. Pen, watercolor, charcoal etc

Some NPR systems emulate an artist’s hand-work Pen & Ink illustration

Watercolor painting( 수채화 )

Indian ink painting( 수묵화 )

NPR(Non-Photorealistic Rendering)

Conclusion

기반 기술 개발 추진 체계

응용 기술 추진 체계

참고 )Terminator II : 70 여대의 SGI, 60 여명의 staff, 10 만 line 의 in-house S/W

CG 이론

연관학문의 이론새로운 S/W 개발

모델링 : 계산기하학 , 물리학 , 기계공학 렌더링 : 물리학 , 조명학 애니메이션 : 물리학 , 수학 , 제어공학 가상현실 : 전자공학 , 감성공학

디자이너 그룹 : 아이디어 제공

엔지니어 그룹 : 관련기술 제공새로운 영상물 창조

R & D 그룹 : 기반기술 제공

In-house S/W 개발