1. Introduction to
Computer Graphics
- Introduction -
Marcus Magnor
Computer Graphics WS05/06 - Introduction
Overview
• Today
– Administrative stuff
– Overview of computer graphics
– Fundamentals of image formation
• Next time
– Ray tracing fundamentals
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2. General Information
• Blockveranstaltung
– 3+1
– Tue, Wed, Th 11.30-13.00 h
– Room M160
• Assignments
– Weekly
• Th – Tue next week
– practical assignments
• Program your own ray tracer
• Provisional web page
– http://www.mpi-
inf.mpg.de/departments/irg3/ws0506/cg/index.html
– Lecture slides (PDF), assignments, other information
Computer Graphics WS05/06 - Introduction
People
• Lecturer
– Prof. Marcus Magnor
• Room G29
• E-mail: magnor@mpi-sb.mpg.de
• Assistant
– Andrei Lintu
• At MPII
• Tel. 0681/9325-527
• E-mail: lintu@mpi-sb.mpg.de
• Secretary
– Dr. Marion Zeiz
• Room G28
• Tel. 391-2102
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3. Weekly Assignments
• Weekly assignments (Th to Tue)
– Programming assignments
– Submit your solution by following Tuesday
• E-mail program code to Andrei Lintu
– Feedback
• Correct program code provided on web page
• Discussion, Q&A via e-mail (chat ?)
Computer Graphics WS05/06 - Introduction
Programming Assignments
• On computers in student pool
– Standard ANSI C/C++
– Must compile on any Linux system
• Send in compile-alone source code
– Standard libraries, library paths
– Provide Makefile
– Must compile and run on any Linux box
• Basis for ray tracing competition
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4. Ray Tracing Competition
At the end of semester
• Technical part: implement additional techniques
– Points for each implemented technique
• Bump mapping
• Shadow mapping
• Motion blur
• …
• Artistic part: create your own ray-traced work of art
– Picture must reflect all additionally implemented techniques
– Awards for best pictures
– Virtual exhibition on our web pages
Computer Graphics WS05/06 - Introduction
To pass the course
• Programming assignments
– Minimum of 30% per assignment sheet
– Average of >50% of all assignments
• Ray Tracing competition
– Submit a picture created with your enhanced ray tracer
– Create accompanying web page explaining your techniques etc.
– Implement minimum number of technical points
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5. Literature
– Frank Nielsen, "Visual Computing", Charles River Media, 2005,
EUR 55,90
– Peter Shirley, "Realistic Ray-Tracing", AK Peters, 2003, EUR 40,00
– Alan Watt, Mark Watt, "Advanced Animation and Rendering
Techniques,“ Addison-Wesley, 1992, EUR 55,50
– Peter Shirley et al., "Fundamentals of Computer Graphics", AK
Peters, 2005, EUR 81,50
– James Foley, Andries Van Dam, et al., "Computer Graphics:
Principles and Practice", 2. Edition, Addison-Wesley, 1995, EUR
81,50
Computer Graphics WS05/06 - Introduction
Course Syllabus
• Fundamentals
– light transport
• Ray Tracing
– Basics
– Transformations and projections
– Acceleration strategies
– Signal processing, antialiasing
• Advanced Topics
– Human visual system
– Perception
– Global illumination
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6. What is Computer Graphics ?
Engineering
Photography Psychology
CAD/CAM/CAE
Rendering Perception
Graphics
Simulation Inverse Rendering
Geometric
Physics Modeling Vision
Mathematics
Computer Graphics WS05/06 - Introduction
Image Perception - Image Formation
Scene Geometry
Motion
Models Surface Reflectance Physics
Scene Illumination
Camera
Analysis Synthesis
Image
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7. Historical Perspective
• A short history of graphics:
– 1950: MIT Whirlwind (CRT)
– 1955: Sage, Radar with CRT and light pen
– 1958: Willy Higinbotham “Tennis”
– 1960: MIT „Spacewar“ on DEC PDP-1
– 1963: Ivan Sutherland‘s „Sketchpad“ (CAD)
– 1969: ACM Siggraph founded
– 1968: Tektronix storage tube ($5-10.000)
– 1968: Evans&Sutherland (flight simulators) founded
– 1968: Douglas Engelbart: computer mouse
– 1970: Xerox: GUI
– 1971: Gourand shading
– 1974: Z-buffer
– 1975: Phong model
– 1979: Eurographics founded
– 1980: Whitted: Ray tracing
Computer Graphics WS05/06 - Introduction
Historical Perspective
• A short history of graphics (Cont.):
– 1981: Apollo Workstation, IBM PC
– 1982: Silicon Graphics (SGI) founded
– 1984: X Window System
– 1984: First Silicon Graphics Workstations (IRIS GL)
– Until mid/end of 1990s: Dominance of SGI in the high end
• HW: RealityEngine, InfiniteReality, RealityMonster, ...
• SW: OpenGL, OpenInventor, Performer, Digital Media Libs, ...
– End of 1990s:
Low- to mid range taken over by „PCs“ (Nvidia, ATI, ...)
• HW: Fast development cycles, Graphics-on-a-chip, ...
• SW: Direct 3D & OpenGL, computer games
– Today
• Programmable graphics hardware, Cg
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8. Visual Entertainment
1995 1996 1997 1998 1999 2000 2001 2002
(1) No. released Movies 280 287 286 287 327 373 338 321
(Germany)
(2) Movie Theater Revenue 605 672 750 818 808 824 987
(Germany, in Mio. Euro)
(3) No. released Computer 1107 1039 823 696 849 932 949 1211
Games (Germany)
(4) Game Industry Revenue 1479 1572 1617 1527
(Germany , in Mio. Euro)
(1) Quelle: SPIO, Spitzenorganisation der Filmwirtschaft, Wiesbaden
(2) Quelle: FFA, Filmförderanstalt, Berlin
(3) Quelle: Titelprüfung der USK für Computerspiele (aller Systeme), entspricht rd. 95% aller auf dem dt. Markt publizierten Produktionen
(4) Quelle: Gfk, Gesellschaft für Konsumforschung; zitiert nach VUD, Verband Unterhaltssoftware Dtld. e.V.
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Siggraph Publications 2001-2005
Siggraph 2001-2005
300
250
200
271
# publications 150
100
50
11 10 7
27 26 26 22 16
0
USA Germany Canada China France Israel Japan Suisse UK
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9. Computer Graphics Industry
• Graphics hardware • Interactive entertainment
– NVidia (USA) – Electronic Arts (USA)
– ATI (Canada) • HEADQUARTERS: Redwood
City, California
• Software research
• REVENUES: $3.1 billion for
– Microsoft (USA, UK, China)
fiscal 2005
• Animation software • EMPLOYEES: 6,100
– Alias (Canada) worldwide
– Avid/SoftImage (USA/Canada) – Sony, Nintendo, Sega (Japan)
– Autodesk (USA) – Ubi Soft (France)
• F/X
– Industrial Light & Magic (USA)
– Digital Domain (USA)
– Pixar (USA)
Computer Graphics WS05/06 - Introduction
Industrial CG Jobs in Germany
• CAD, VR
– Airbus (Hamburg)
– Automotive industry
Small- & mid-cap companies
• Animation
– http://www.rendering.de/nano.cms/Lightwave/Jobangebote
• Game development
– Bundesverband der interaktiven Unterhaltungssoftware
– http://www.game-verband.de/
• Ubi Soft (Düsseldorf)
• Radon Labs, Zeroscale, SEK (Berlin)
• Crytek (Coburg)
• CG Research
– “Mental Images”, “Mercury” (Berlin)
– “Alias”, “Scanline” (Munich)
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10. Summary
• Computer Graphics
– Rendering, modeling, visualization, animation, imaging, …
• Young, dynamic area
– Progress driven by research & technology
• Big industry
– >> interactive entertainment, special effects
• Interdisciplinary field
– Mathematics, physics, engineering, psychology, art, entertainment,
…
Computer Graphics WS05/06 - Introduction
Introduction to
Computer Graphics
- Image Formation -
Marcus Magnor
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11. Motivation
Photography Computer Graphics
• Easy acquisition • Time-consuming scene modeling
• Fast display • Computation-intensive rendering
• Natural impression • Artifical appearance
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Image Formation
Sensor Transfer/
Storage
Light propagation
Imaging optics
Light/Object interaction
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12. Perception of Light
dΩ
r dΩ' dA
f l
photons / second = flux = energy / time = power Φ rod detects flux
angular extend of rod = resolution (≈ 1 arc minute^2) dΩ
projected rod size = area dA ≈ l 2 ⋅ dΩ
Angular extend of pupil aperture (r ≤ 4 mm) = solid angle dΩ ' ≈ π ⋅ r 2 / l 2
flux proportional to area and solid angle Φ ∝ dΩ'⋅dA
Φ
radiance = flux per unit area per unit solid angle L=
dΩ'⋅dA
The eye detects radiance
Computer Graphics WS05/06 - Introduction
Radiance in Space
dΩ2 dΩ1
L1 L2
l
dA1 dA2
Flux leaving surface 1 must be equal to flux arriving on surface 2
L1 ⋅ dΩ1 ⋅ dA1 = L2 ⋅ dΩ 2 ⋅ dA2
dA2 dA1
From geometry follows dΩ1 = dΩ 2 =
l2 l2
dA ⋅ dA
Ray throughput T = dΩ1 ⋅ dA1 = dΩ 2 ⋅ dA2 = 1 2 2
l
L1 = L2
The radiance in the direction of a light ray
remains constant as it propagates along the ray
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13. Brightness Perception
dΩ
r dΩ' dA
dA'
f l
r2
As l increases: Φ 0 ∝ dA ⋅ dΩ' = l 2 dΩ ⋅ π = const
l2
• dA’ > dA : photon flux per rod stays constant
• dA’ < dA : photon flux per rod decreases
Where does the Sun turn into a star ?
− Depends on apparent Sun disc size on retina
Photon flux per rod stays the same on Mercury, Earth or Neptune
Photon flux per rod decreases when dΩ’ < 1 arc minute (beyond Neptune)
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Light – Object Interaction
Light/Object interaction
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14. Reflectance
• Reflectance may vary with
– Illumination angle
– Viewing angle
– Wavelength
– (Polarization)
• Variations due to
– Absorption
Aluminium; =2.0 m ¡
– Surface micro-geometry
– Index of refraction / dielectric constant
– Scattering
Aluminium; =0.5 m ¡
Magnesium; =0.5 m ¡
Computer Graphics WS05/06 - Introduction
Surface Radiance
• Visible surface radiance L ( x, ω o ) ωo
– Surface position x
ωi
– Outgoing direction ωo θi
– Incoming illumination ωi
direction
Le ( x, ω o )
x
• Self-emission
• Reflected light Li ( x, ω i )
– Incoming radiance from all directions
– Direction-dependent reflectance f r ( x, ω i → ω o )
Lo ( x, ω o ) = Le ( x, ω o ) + f r ( x, ω i → ω o ) Li ( x, ω i ) cos θ i d ω i
Ω
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15. Bidirectional Reflectance Distribution Function
• BRDF describes surface reflection for light incident from
direction ( , ) observed from direction ( i, i)
¤£ ¢
¡ ¡ £
• Bidirectional
– depends on two directions (4-D function)
• Distribution function
• Unit [1/sr]
Lo (ω o )
f r (ω o , ω i ) =
dEi (ω i )
Lo (ω o )
=
Li (ω i ) cos θ i d ω i
Computer Graphics WS05/06 - Introduction
BRDF Properties
• Helmholtz reciprocity principle
– BRDF remains unchanged if incident and reflected directions are
interchanged
ρ bd (θ o , ϕ o ,θ , ϕ ) = ρ bd (θ , ϕ ,θ o , ϕ o )
• Smooth surface: isotropic BRDF
– reflectivity independent of rotation around surface normal
– BRDF has only 3 instead of 4 degrees of freedom
ρ bd (θ o ,θ , ϕ o − ϕ )
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16. BRDF Properties
• Characteristics
– BRDF units [sr--1]
• not intuitive
– Range of values:
• from 0 (absorption) to
• ∞ (reflection, -function)
– Energy conservation law
• No self-emission
• Possible absorption
ρ bd (θ o , φo ,θ , ϕ ) cos θ o dω o ≤ 1 ∀ θ , ϕ
Ω
– Reflection only at the point of entry (xi = xo)
• No subsurface scattering
Computer Graphics WS05/06 - Introduction
BRDF Measurement
• Gonio-Reflectometer
• BRDF measurement
– point light source position (θ,ϕ)
– light detector position (θo ,ϕo)
• 4 degrees of freedom
• BRDF representation
– m incident direction samples (θ,ϕ)
– n outgoing direction samples (θo ,ϕo)
– m*n reflectance values
Stanford light gantry
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17. Wrap-Up
• What you perceive is radiance
• Different objects reflect light differently:
Bidirectional Reflectance Distribution Function (BRDF)
• Light can be absorbed, scattered, bent, …
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