01.1Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Computer Graphics: 1980-1990

Realism comes to computer graphics

smooth shading environment mapping

bump mapping

01.2Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Computer Graphics: 1980-1990

Special purpose hardwareSilicon Graphics geometry engine

• VLSI implementation of graphics pipeline

Industry-based standardsPHIGSRenderMan

Networked graphics: X Window SystemHuman-Computer Interface (HCI)

01.3Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Computer Graphics: 1990-2000

OpenGL APICompletely computer-generated feature-length movies (Toy Story) are successful

New hardware capabilitiesTexture mappingBlendingAccumulation, stencil buffers

01.4Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Computer Graphics: 2000-

PhotorealismGraphics cards for PCs dominate market

Nvidia, ATI, 3DLabs

Game boxes and game players determine direction of market

Computer graphics routine in movie industry: Maya, Lightwave

Programmable pipelines

01.5Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Image Formation

01.6Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Objectives

Fundamental imaging notionsPhysical basis for image formation

LightColorPerception

Synthetic camera modelOther models

01.7Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Image Formation

In computer graphics, we form images which are generally two dimensional using a process analogous to how images are formed by physical imaging systemsCamerasMicroscopesTelescopesHuman visual system

01.8Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Elements of Image Formation

ObjectsViewerLight source(s)

Attributes that govern how light interacts with the materials in the scene

Note the independence of the objects, the viewer, and the light source(s)

01.9Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Light

Light (cahaya) bagian dari spektrum elektromagnet yang dapat bereaksi terhadap sistem visual kita

wavelengths pada rentang 350-780 nm (nanometers)

Long wavelengths merah dan short wavelengths sebagai biru

01.10Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Ray Tracing and Geometric Optics

Salah satu cara pembentukan image, denganmengikuti sinar cahaya dari titik sumber hinggatitik masuknya cahaya pada lensa. meskipun, Tiap sinar cahaya memungkinkan mengalami beragam interaksi misalkanhingga terabsorbsinya oleh objek ataupun menuju titik infinity.

01.11Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Luminance and Color Images

Luminance ImageMonochromatic Values are gray levelsAnalogous to working with black and white film

or television

Color ImageHas perceptional attributes of hue, saturation,

and lightnessDo we have to match every frequency in visible

spectrum? No!

01.12Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Three-Color Theory

Human visual system has two types of sensorsRods (batang): monochromatic, night visionCones

• Color sensitive• Three types of cones• Only three values (the tristimulus

values) are sent to the brain

Need only match these three valuesNeed only three primary colors

01.13Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Shadow Mask CRT

01.14Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Additive and Subtractive Color

Additive colorForm a color by adding amounts of three

primaries• CRTs, projection systems, positive film

Primaries are Red (R), Green (G), Blue (B)Subtractive color

Form a color by filtering white light with cyan (C), Magenta (M), and Yellow (Y) filters

• Light-material interactions• Printing• Negative film

01.15Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Pinhole Camera

xp= -x/z/d yp= -y/z/d

Use trigonometry to find projection of point at (x,y,z)

These are equations of simple perspective

zp= -d

01.16Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Synthetic Camera Model

center of projection

image plane

projector

p

projection of p

01.17Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Advantages

Separation of objects, viewer, light sourcesTwo-dimensional graphics is a special case of three-dimensional graphics

Leads to simple software APISpecify objects, lights, camera, attributesLet implementation determine image

Leads to fast hardware implementation

01.18Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Global vs Local Lighting

Cannot compute color or shade of each object independentlySome objects are blocked from lightLight can reflect from object to objectSome objects might be translucent (cahaya

tembus)

01.19Angel: Interactive Computer Graphics 4E @ Addison-Wesley 2005

Why not ray tracing?

Ray tracing seems more physically based so why don’t we use it to design a graphics system?

Possible and is actually simple for simple objects such as polygons and quadrics with simple point sources

In principle, can produce global lighting effects such as shadows and multiple reflections but ray tracing is slow and not well-suited for interactive applications