Prof.Dr. Aydın Öztürk

Objectives: The course gives the fundementals of computer graphics. A subset of topics dealing with two-dimensional drawing methods and graphics primitives will be discussed

Grading Midterm25 Assignments25 Project50 Final- Attendance 10

Course Outline Mathematics for Computer Graphics Overview of Graphics Systems Graphics Output Primitives Attributes of Graphics Primitives Geometric Transformations Two-dimensional Viewing Midterm Interactive Input Methods and Graphical User Interfaces Color Models and Color Applicatios Computer Animation Final

Rules Attendance is required at all times. Students are expected to come to class fully prepared to discuss textbook readings and course assignments. Some percentage of your final grade will be based on your attendance and class participation.

 Computer Graphics with OpenGL ▪ Third Edition ▪ Hearn and Baker

 Computer Graphics Using OpenGL, 3rd edition/2005, F.S.Hill, Jr. Prentice Hall  OpenGL Programming Guide, Version 2, 5th edition, D. Shreiner,M.Woo, J.Neider, T.Davis, Addison-Wesley, 2005, ISBN:

Computer graphics: generating 2D images of a 3D world represented in a computer. Main tasks:  modeling: creating and representing the geometry of objects in the 3D world  rendering: generating 2D images of the objects  animation: describing how objects change in time

Graphics is cool  I like to see what I’m doing  I like to show people what I’m doing Graphics is interesting  Involves simulation, algorithms, architecture… I’ll never get an Oscar for my acting  But maybe I’ll get one for my CG special effects Graphics is fun

Entertainment: Cinema Pixar: Monster’s Inc. Square: Final Fantasy

Final Fantasy (Square, USA) Entertainment: Cinema

Entertainment: Games GT Racer 3 Polyphony Digital: Gran Turismo 3, A Spec

Video Games

Medical Visualization MIT: Image-Guided Surgery Project The Visible Human Project

Computer Aided Design (CAD)

Scientific Visualization

Everyday Use  Microsoft’s Whistler OS will use graphics seriously  Graphics visualizations and debuggers  Visualize complex software systems

Window system and large-screen interaction metaphors (François Guimbretière)

Outside In (Geometry Center, University of Minnesota)

Reflection models Reference Image Copula-Frank Blue-Metallic Paint

Moore’s Law Power of a CPU doubles every 18 months / 2 years

Number of transistors on GPU doubles each 6 months.  Three times Moore’s Law ▪ Good article on Jen-Hsun Huang, Nvidia CEO: $7 Billion Man $5.6 Billion Man Worldwide revenues Retro flashback??? Lee Majors Col. Steve Austin

But…  Video game sales is roughly same as Hollywood box office  Americans bought $3.2 billion in VCRs and DVDs in 2002  Total revenues to movie studios is 5 times total video game revenues

Cathode Ray Tubes (CRTs)  Most common display device today  Evacuated glass bottle  Extremely high voltage

 Heating element (filament)  Electrons pulled towards anode focusing cylinder  Vertical and horizontal deflection plates  Beam strikes phosphor coating on front of tube

Contains a filament that, when heated, emits a stream of electrons Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube The front surface of the picture tube is coated with small phospher dots When the beam hits a phospher dot it glows with a brightness proportional to the strength of the beam and how long it is hit

What’s the largest (diagonal) CRT you’ve seen?  Why is that the largest? ▪ Evacuated tube == massive glass ▪ Symmetrical electron paths (corners vs. center) How might one measure CRT capabilities?  Size of tube  Brightness of phosphers vs. darkness of tube  Speed of electron gun  Width of electron beam  Pixels?

Vector Displays

 Early computer displays: basically an oscilloscope  Control X,Y with vertical/horizontal plate voltage  Often used intensity as Z Name two disadvantages  Just does wireframe  Complex scenes couse visible flicker

Raster Displays  Raster: A rectangular array of points or dots  Pixel: One dot or picture element of the raster  Scan line: A row of pixels

Raster Displays  Black and white television: an oscilloscope with a fixed scan pattern: left to right, top to bottom ▪ As beam sweeps across entire face of CRT, beam intensity changes to reflect brightness  Analog signal vs. digital display

Can a computer display work like a black and white TV?  Must synchronize ▪ Your program makes decisions about the intensity signal at the pace of the CPU… ▪ The screen is “painted” at the pace of the electron gun scanning the raster  Solution: special memory to buffer image with scan-out synchronous to the raster. We call this the framebuffer.  Digital description to analog signal to digital display

Phosphers  Flourescence: Light emitted while the phospher is being struck by electrons  Phospherescence: Light emitted once the electron beam is removed  Persistence: The time from the removal of the excitation to the moment when phospherescence has decayed to 10% of the initial light output

Refresh  Frame must be “refreshed” to draw new images  As new pixels are struck by electron beam, others are decaying  Electron beam must hit all pixels frequently to eliminate flicker  Critical fusion frequency ▪ Typically 60 times/sec ▪ Varies with intensity, individuals, phospher persistence, lighting...

Raster Displays  Interlaced Scanning  Assume can only scan 30 times / second  To reduce flicker, divide frame into two “fields” of odd and even lines 1/30 Sec 1/60 Sec Field 1 Field 2 Frame

CRT timing  Scanning (left to right, top to bottom) ▪ Vertical Sync Pulse: Signals the start of the next field ▪ Vertical Retrace: Time needed to get from the bottom of the current field to the top of the next field ▪ Horizontal Sync Pulse: Signals the start of the new scan line ▪ Horizontal Retrace: The time needed to get from the end of the current scan line to the start of the next scan line

Wood chips Chrome spheres Trash Daniel Rozin – NYU: (movies)

Color CRTs are much more complicated  Requires manufacturing very precise geometry  Uses a pattern of color phosphors on the screen:  Why red, green, and blue phosphors? Delta electron gun arrangementIn-line electron gun arrangement

Color CRTs have  Three electron guns  A metal shadow mask to differentiate the beams

Raster CRT pros:  Allows solids, not just wireframes  Leverages low-cost CRT technology (i.e., TVs)  Bright! Display emits light Cons:  Requires screen-size memory array  Discreet sampling (pixels)  Practical limit on size (call it 40 inches)  Bulky  Finicky (convergence, warp, etc)

 CRT technology hasn’t changed much in 50 years  Early television technology ▪ high resolution ▪ requires synchronization between video signal and electron beam vertical sync pulse  Early computer displays ▪ avoided synchronization using ‘vector’ algorithm ▪ flicker and refresh were problematic

 Raster Displays (early 70s) ▪ like television, scan all pixels in regular pattern ▪ use frame buffer (video RAM) to eliminate sync problems  RAM ▪ ¼ MB (256 KB) cost $2 million in 1971 ▪ Do some math… x 1024 screen resolution = 1,310,720 pixels - Monochrome color (binary) requires 160 KB - High resolution color requires 5.2 MB

Liquid Crystal Displays (LCDs)  LCDs: organic molecules, naturally in crystalline state, that liquefy when excited by heat or E field  Crystalline state twists polarized light 90º

Transmissive & reflective LCDs:  LCDs act as light valves, not light emitters, and thus rely on an external light source.  Laptop screen ▪ backlit ▪ transmissive display  Palm Pilot/Game Boy ▪ reflective display

Plasma display panels  Similar in principle to fluorescent light tubes  Small gas-filled capsules are excited by electric field, emits UV light  UV excites phosphor  Phosphor relaxes, emits some other color

Plasma Display Panel Pros  Large viewing angle  Good for large-format displays  Fairly bright Cons  Expensive  Large pixels (~1 mm versus ~0.2 mm)  Phosphors gradually deplete  Less bright than CRTs, using more power

Digital Micromirror Devices (projectors) or Digital Light Processing  Microelectromechanical (MEM) devices, fabricated with VLSI techniques

DMDs are truly digital pixels Vary grey levels by modulating pulse length Color: multiple chips, or color-wheel Great resolution Very bright Flicker problems

Organic Light-Emitting Diode (OLED) Arrays  The display of the future? Many think so.  OLEDs function like regular semiconductor LEDs  But they emit light ▪ Thin-film deposition of organic, light-emitting molecules through vapor sublimation in a vacuum. ▪ Dope emissive layers with fluorescent molecules to create color.

OLED pros:  Transparent  Flexible  Light-emitting, and quite bright (daylight visible)  Large viewing angle  Fast (< 1 microsecond off-on-off)  Can be made large or small  Available for cell phones and car stereos

OLED cons:  Not very robust, display lifetime a key issue  Currently only passive matrix displays ▪ Passive matrix: Pixels are illuminated in scanline order, but the lack of phospherescence causes flicker ▪ Active matrix: A polysilicate layer provides thin film transistors at each pixel, allowing direct pixel access and constant illum.

Display Walls (Princeton)

Stereo

Graphics Hardware  Frame buffer is anywhere in system memory System Bus CPUVideo Controller System Memory Monitor Frame buffer Cartesian Coordinates

Graphics Hardware  Permanent place for frame buffer  Direct connection to video controller System Bus CPUVideo Controller System Memory Monitor Frame buffer Cartesian Coordinates Frame Buffer

The need for synchronization System Bus CPUVideo Controller System Memory Monitor Frame Buffer synchronized

The need for synchronization  Double buffering System Bus CPUVideo Controller System Memory Monitor Double Buffer synchronized previouscurrent

Display Processor Display Processor System Memory System Memory CPU Frame Buffer Frame Buffer Monitor Video Controller Video Controller System Bus I/O Devices Figure 2.29 from Hearn and Baker

DAC Store the actual intensities of R, G, and B individually in the framebuffer 24 bits per pixel = 8 bits red, 8 bits green, 8 bits blue  16 bits per pixel = ? bits red, ? bits green, ? bits blue

Store indices (usually 8 bits) in framebuffer Display controller looks up the R,G,B values before triggering the electron guns Frame Buffer DAC Pixel color = 14 Color Lookup Table R G B

Figure. Renderings of spheres based on the measured “blue-metallic-paint” [2] BRDF with the eight models. From left to right; Top row: Measured, Ashikhmin-Shirley, Blinn-Phong, Cook-Torrance, Lafortune, Polynomial model (Ashikhmin-Shirley, p=3). Bottom row: Oren-Nayar, Ward, Ward-Duer, Polynomial model (Lafortune, p=5), Polynomial model (Ward, p=5).

Figure. Renderings of a car using copula-based model with different enviroment maps.