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  • 1. Introduction to Computer Graphics - Introduction - Marcus MagnorComputer Graphics WS05/06 - IntroductionOverview • Today – Administrative stuff – Overview of computer graphics – Fundamentals of image formation • Next time – Ray tracing fundamentalsComputer Graphics WS05/06 - Introduction 1
  • 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 informationComputer Graphics WS05/06 - IntroductionPeople • 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. 391-2102Computer Graphics WS05/06 - Introduction 2
  • 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 - IntroductionProgramming 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 competitionComputer Graphics WS05/06 - Introduction 3
  • 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 pagesComputer Graphics WS05/06 - IntroductionTo 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 pointsComputer Graphics WS05/06 - Introduction 4
  • 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 81,50Computer Graphics WS05/06 - IntroductionCourse Syllabus • Fundamentals – light transport • Ray Tracing – Basics – Transformations and projections – Acceleration strategies – Signal processing, antialiasing • Advanced Topics – Human visual system – Perception – Global illuminationComputer Graphics WS05/06 - Introduction 5
  • 6. What is Computer Graphics ? EngineeringPhotography Psychology CAD/CAM/CAE Rendering Perception Graphics Simulation Inverse Rendering Geometric Physics Modeling Vision MathematicsComputer Graphics WS05/06 - Introduction Image Perception - Image Formation Scene Geometry Motion Models Surface Reflectance Physics Scene Illumination Camera Analysis Synthesis ImageComputer Graphics WS05/06 - Introduction 6
  • 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 tracingComputer Graphics WS05/06 - IntroductionHistorical 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, CgComputer Graphics WS05/06 - Introduction 7
  • 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 1211Games (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. Computer Graphics WS05/06 - Introduction 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 Computer Graphics WS05/06 - Introduction 8
  • 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 - IntroductionIndustrial 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)Computer Graphics WS05/06 - Introduction 9
  • 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 MagnorComputer Graphics WS05/06 - Introduction 10
  • 11. Motivation Photography Computer Graphics • Easy acquisition • Time-consuming scene modeling • Fast display • Computation-intensive rendering • Natural impression • Artifical appearanceComputer Graphics WS05/06 - IntroductionImage Formation Sensor Transfer/ Storage Light propagation Imaging opticsLight/Object interactionComputer Graphics WS05/06 - Introduction 11
  • 12. Perception of Light dΩ r dΩ dA f lphotons / second = flux = energy / time = power Φ rod detects fluxangular extend of rod = resolution (≈ 1 arc minute^2) dΩprojected rod size = area dA ≈ l 2 ⋅ dΩAngular extend of pupil aperture (r ≤ 4 mm) = solid angle dΩ ≈ π ⋅ r 2 / l 2flux proportional to area and solid angle Φ ∝ dΩ⋅dA Φradiance = 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 dA1From geometry follows dΩ1 = dΩ 2 = l2 l2 dA ⋅ dARay 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 Computer Graphics WS05/06 - Introduction 12
  • 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 decreasesWhere 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)Computer Graphics WS05/06 - IntroductionLight – Object Interaction Light/Object interactionComputer Graphics WS05/06 - Introduction 13
  • 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 - IntroductionSurface 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 ΩComputer Graphics WS05/06 - Introduction 14
  • 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 iComputer Graphics WS05/06 - IntroductionBRDF 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 )Computer Graphics WS05/06 - Introduction 15
  • 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 scatteringComputer Graphics WS05/06 - IntroductionBRDF 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 gantryComputer Graphics WS05/06 - Introduction 16
  • 17. Wrap-Up • What you perceive is radiance • Different objects reflect light differently: Bidirectional Reflectance Distribution Function (BRDF) • Light can be absorbed, scattered, bent, …Computer Graphics WS05/06 - Introduction 17