Post on 20-Jan-2016
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