Introduction to Computer Graphics: ITCS 4120/5120 Dr. Zachary Wartell Revision 1.2 2/16/07 Copyright...

Introduction to Computer Graphics: ITCS 4120/5120

Dr. Zachary Wartell

Revision 1.22/16/07

Copyright 2006, Dr. Zachary Wartell, UNCC, All Rights Reserved

Introduction to Computer Graphics: ITCS 4120/5120

Professor: Dr. Zachary Wartell www.cs.uncc.edu/~zwartell

TA: unknown

Textbook: Computer Graphics with OpenGL, Hearn & Baker

Suggested (depending on background):-C++ for Java Programmers, Timothy Budd, 1999.-C++ Primer Plus: Teach Yourself Object-Oriented

Programming, Stephen Prata

©Zachary Wartell

Prerequisites for ITCS 4120/5120

Juniors/Seniors/Masters/Ph.D. StudentsMATH 2164: Matrices and Linear Algebra ITCS 2214: Data StructuresStrong programming and debugging skills!

Languages: -you know C++ or -you know Java - & understand low-level programming such as:

-ITCS 3182 Computer Organization and Architecture or -ITCS 3110 Compiler Construction or -have programmed in C

- & capable of learning a new language on your own

©Zachary Wartell

Tools for Programming Projects in ITCS 4120/5120

C++ Microsoft Visual Studio 2005

Woodward 335COIT/BISOM students MSDNAA: http://www.labs.uncc.edu/basics/compguide.html

OpenGL – [MSVC 2005] – 2D/3D graphics API libraryFLTK – [class website] – GUI API librarySVN – [class website] - source code revision control system. Used for turning in projects.

Assignments are best done in Woodward 335Tools and API’s have been tested in 335

©Zachary Wartell

http://www.labs.uncc.edu/basics/compguide.html

Author

Comment

What is computer graphics (CG)?

It’s a core software & hardware technology in:

-Computer Aided Design (CAD)-Scientific Visualization-Medical Visualization-Education-Computer Interfaces-Computer/Video Games-Virtual Reality & Visual Simulation-Movies

©Zachary Wartell

CG: a core technology in CAD

AutoCADTM

5SpiceTM

©Zachary Wartell

CG: a core technology in Scientific Visualization

Weather

Molecular Vis.

©Zachary Wartell

CG: a core technology in Medical Visualization

©Zachary Wartell

CG: a core technology in Computer Interfaces

Microsoft Windows GNOME

Mac OS X©Zachary Wartell

CG: a core technology in Games

FarCry (UbiSoft)

Falcon 4.0(Microprose)

Zelda (Nitendo)©Zachary Wartell

CG: a core technology in VR & Vis. Sim.

Exposure Therapy for Flying Phobia(Larry Hodges et.al)

Pilot Training(AlSim, Inc.)

©Zachary Wartell

CG: a core technology in VR & Vis. Simulation

Two-hand Interfacefor Weather Vis.

“Holospace” Surround ScreenDisplay(Barco)

©Zachary Wartell

CG: a core technology in Movies

Star Wars: Episode IITM(LucusFilm)

Shrek 2TM(Dreamworks)

©Zachary Wartell

What disciplines does CG technology draw on?

algorithmsmath

-basic graphics (ITCS 4120) – linear/vector algebra, geometry & trig.

-advanced graphics advanced calculus, computational geometry, differential geometry, topology, …..

optics (very approximate in ITCS 4120) software engineering and programminghardware engineeringpsychophysics (branch of psychology)

-human visual systemindustrial art & design

©Zachary Wartell

ITCS 4120 subset of these disciplines

ITCS 4120: Lecture Material45% - algorithms45% - math (linear/vector algebra, geometry & trig.)3% - optics3% - hardware engineering3% - psychophysics1% - programming

ITCS 4120: Projects50(?)% - programming (C++, OpenGL, FLTK)50(?)% - deeply understanding Lecture Material

“you don’t really understand it until you’ve implemented it”

©Zachary Wartell

How long has CG been around?

Ivan Sutherland, SketchPad, 1963 MIT

CRT, light-pen, direct-manipulation 2D graphics

©Zachary Wartell

How long has CG been around?

William Fetter, 1960, Boeing Aircraft Co.

“Boeing Man”, human figure simulation, credited with “computer graphics”

©Zachary Wartell

In what way do CG applications differ?

2D versus 3DSpeed – Frames Per Second (FPS)

Realism

vs$$$

1950’s, Whirlwind, $4.5M, 40K adds/s today’s PC: $1K, 2-3B ops/s

CG: 1995, $100K, SGI = 2004, $1K PC©Zachary Wartell

General Interactive Movies Application Games Visual Simulation(time) hours 200 ms 33ms 16 ms

(FPS) 0.0xx 5-15 15-60 60+

Frames Per Second Interactive Graphics

Differences in CG applications: Speed

Speed: Time to compute one image

FASTER

©Zachary Wartell

Realism- more math, more physics → more realism (real-time CG → ray-tracing → radiosity → “rendering equation”)

- display technology & human visual perception (image fidelity, stereopsis, motion parallax)

Differences in across CG applications: Realism

More Photo Realistic

“Cartoon” Movie Special Product Games Vis. Sim. Movies FX Evaluation

©Zachary Wartell

CG: Speed vs. Realism

generally: more realism → less speed

but Moore’s Law continues to reign-price/performance improves 2x every 18 months-since 1995 gaming market driving

graphics hardware

-Nintendo GameCubeTM (ATI)-XboxTM (Nvidia inside)-PC: nVidia Geforce 7900, ATI Radeon X1900

display capability still lags human eye’s precision (but there is substantial and continuing advances)

©Zachary Wartell

What are a CG application’s components?

Eye Brain

Display

Input Device

Body

CG System Software

OS

CG 3D API CG GUI (2D) API

ApplicationSoftware

General Computing Hardware

Graphics Computing Hardware

Image Synthesis

©Zachary Wartell

Image Synthesis Processes

Image Synthesis

Modeling: The process of creating objects of a scene that will berendered by the graphics hardware.

Viewing: Specification of camera and a viewing windowthat determines the part of the world (of objects) that will be includedin the final image.

Rendering: The process that creates an image of the objects withinthe current view, taking into account lighting parameters and materialcharacteristics.

Modeling Viewing Rendering

©Zachary Wartell, K.R. Subramanian

2D Image Synthesis: Coordinate Systems (CS)

2D World2D Models

Model CS World CS

View(2D Window)

World CS

View Transform(2D→2D)

ConvertGeometry to Image

CoordinateTransforms

2D Image

[Display] Device CS(DCS)

- Computation

- Data

©Zachary Wartell

3D Image Synthesis: Coordinate Systems (CS)

3D World3D Models

View(Eye &

Window)View

Transform(3D→2D)

ConvertGeometry to Image

CoordinateTransforms

2D Image


World CS Model CS

World CS

Lights

- Computation

- Data

©Zachary Wartell

Image Data Structures & Display Hardware

Slide 22

Slide 20

Slide 20

So far: CG application components, Image Synthesis, Coordinate Systems. Let’s start with details about:

©Zachary Wartell

2D Image


2D Image



Graphics ComputingHardware


Graphics ComputingHardware

Display

©Larry F. Hodges, Zachary Wartell

Basic Definitions

RASTER: A rectangular array of points or dots (either on physical display or a data structure in memory).

PIXEL (Pel): One dot or picture element of the raster

SCAN LINE: A row of pixels

Raster Displays create display an image by sequentially drawing out the pixels of the scan lines that form the raster.

Pixel

• Pixel - The most basic addressable element in a image or on a display

– CRT - Color triad (RGB phosphor dots)

– LCD - Single color element

• Resolution - measure of number of pixels on a image (m by n)

– m - Horizontal image resolution

– n - Vertical image resolution


Other meanings of resolution

• Dot Pitch [Display] - Size of a display pixel, distance from center to center of individual pixels on display

• Cycles per degree [Display] - Addressable elements (pixels) divided by twice the FOV measured in degrees.

• Cycles per degree [Eye] - The human eye can resolve 30 cycles per degree (20/20 Snellen acuity).



Basic Image Synthesis Hardware (Raster Display)

DisplayProcessor Display

ProcessorMemory

FramebufferVideo

Controller

PeripheralDevices

CPU SystemMemory

System Bus

raster imagesfound here

Raster – Bit Depth

• A raster image may be thought of as computer memory organized as a two-dimensional array with each (x,y) addressable location corresponding to one pixel.

• Bit Planes or Bit Depth is the number of bits corresponding to each pixel.

• A typical framebuffer resolution might be

1280 x 1024 x 8

1280 x 1024 x 24

1600 x 1200 x 24


Displaying Color

• There are no commercially available small pixel technologies that can individually change color.

• spatial integration – place “mini”-pixels of a few fixed colors very close together. The eye & brain spatially integrate the “mini”-pixel cluster into a perception of a pixel of arbitrary color

• temporal integration - field sequential color uses red, blue and green liquid crystal shutters to change color in front of a monochrome light source. The eye & brain temporally integrate the result into a perception of pixels of arbitrary color


CRT Display


Focusing System

Electron Guns

Red Input

GreenInput

Blue Input

Deflection Yoke

Shadow Mask

Red, Blue, and Green

Phosphor Dots

CRT

Electron Gun

•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 phosphor dots.

•When the beam hits a phosphor dot it glows with a brightness proportional to the strength of the beam and how often it is excited by the beam.


•Red, Green and Blue electron guns.

•Screen coated with phosphor triads.

•Each triad is composed of a red, blue and green phosphor dot.

•Typically 2.3 to 2.5 triads per pixel.

FLUORESCENCE - Light emitted while the phosphor is being struck by electrons.

PHOSPHORESCENCE - Light given off once the electron beam is removed.

PERSISTENCE - Is the time from the removal of excitation to the moment when phosphorescence has decayed to 10% of the initial light output.

Color CRT


G R B G

B G R B

G R B G


•Shadow mask has one small hole for each phosphor triad.

•Holes are precisely aligned with respect to both the triads and the electron guns, so that each dot is exposed to electrons from only one gun.

•The number of electrons in each beam controls the amount of red, blue and green light generated by the triad.

Shadow Mask

SHADOW MASK

RedGreen

Blue

Convergence Point

Phosphor Dot Screen

CRITICAL FUSION FREQUENCY

•Typically 60-85 times per second for raster displays.

•Varies with intensity, individuals, phosphor persistence, room lighting.

Frame: The image to be scanned out on the CRT.

•Some minimum number of frames must be displayed each second to eliminate flicker in the image.

Scanning An Image


•Display frame rate 30 times per second

•To reduce flicker at lesser bandwidths (Bits/sec.), divide frame into two fields—one consisting of the even scan lines and the other of the odd scan lines.

•Even and odd fields are scanned out alternately to produce an interlaced image.

•non-interlaced also called “progressive”©Larry F. Hodges, Zachary Wartell

Time

Interlaced Scanning

1/30 SEC

1/60 SEC

FIELD 1 FIELD 2

FRAME

1/60 SEC

1/30 SEC

1/60 SEC

FIELD 1 FIELD 2

FRAME

1/60 SEC

(0,0)

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 — Time needed to get from the end of the current scan line to the start of the next scan line.

Scanning


Device CS(alternate conventions)

(0,0)

NTSC – ? x 525, 30f/s, interlaced (60 fld/s)PAL – ? x 625, 25f/s, interlaced (50 fld/s)HDTV – 1920 x 1080i, 1280 x 720pXVGA – 1024x768, 60+ f/s, non-interlacedgeneric RGB – 3 independent video signals and synchronization signal, vary in resolution and refresh rategeneric time-multiplexed color – R,G,B one after another on a single signal, vary in resolution and refresh rate

Example Video Formats


Calligraphic/Vector CRT

older technologyvector file instead of framebufferwireframe engineering drawings flight simulators: combined raster-vector CRT

P0

P1

P0

P1

Line (P0,P1)Video

Controller

©Zachary Wartell

Flat-Panel Displays

©Zachary Wartell

Flat-Panel

Emissive Non-Emissive

LED

CRT(90°deflected)

Plasma

Thin-Filmelectroluminescent

LCD DMD

Active-Matrix(TFT)

Passive-Matrix

Flat-Panel Displays (Plasma)

©Zachary Wartell

Flat-Panel


LED

CRT(90°deflected)

Plasma


LCD DMD

Active-Matrix

Passive-Matrix

ToshibaTM, 42”, Plasma HTDV$4,500 (circa 2005)

Flat-Panel Displays (LED)

©Zachary Wartell

Flat-Panel


LED

CRT(90°deflected)

Plasma


LCD DMD

Active-Matrix

Passive-Matrix

BarcoTM “Light Street” (LED)

Flat-Panel Displays (DMD)

©Zachary Wartell

Flat-Panel


LED

CRT(90°deflected)

Plasma


LCD DMD

Active-Matrix

Passive-Matrix

Digital Micro-mirror (DMD)

4 μm

LCD


• Liquid crystal displays use small flat chips which change their transparency properties when a voltage is applied.

• LCD elements are arranged in an n x m array call the LCD matrix

• Level of voltage controls gray levels.• LCDs elements do not emit light, use backlights

behind the LCD matrix

LCD Components


Small fluorescent tubes

Diffuser

Linear Polarizer

LCD Module Color

Filter

Linear Polarizer

Wavefront distortion

filter

LCD Resolution


LCD resolution is occasionally quoted as number of pixel elements not number of RGB pixels.

Example: 3840 horizontal by 1024 vertical pixel elements = 4M elements

Equivalent to 4M/3 = 1M RGB pixels

"Pixel Resolution" is 1280x1024

dot pitch

LCD


• Passive LCD screens– Cycle through each

element of the LCD matrix applying the voltage required for that element.

– Once aligned with the electric field the molecules in the LCD will hold their alignment for a short time

• Active LCD (TFT)– Each element contains

a small transistor that maintains the voltage until the next refresh cycle.

– Higher contrast and much faster response than passive LCD

– Circa 2005 this is the commodity technology

LCD vs CRT


flat & Lightweight

low power consumption

always some light

pixel response-time (12-30ms)

view angle limitations

resolution interpolation required

heavy & bulky

strong EM field & high voltage

true black

better contrast

pixel response-time not noticeable

inherent multi-resolution support

Recall our generic CG box…..



ProcessorMemory

FramebufferVideo

Controller

PeripheralDevices

CPU SystemMemory

System Bus

Framebuffer


• A frame buffer may be thought of as computer memory organized as a two-dimensional array with each (x,y) addressable location corresponding to one pixel.

• Bit Planes or Bit Depth is the number of bits corresponding to each pixel.

• A typical frame buffer resolution might be

640 x 480 x 16

1280 x 1024 x 24

1920 x 1600 x 24

1-Bit Memory: Monochrome Display(Bit-map Display)


Electron Gun

1 bit 2 levels

3-Bit Color Display


3

red

green

blue

COLOR: black red green blue yellow cyan magenta white

R G B

0 0 0

1 0 0

0 1 0

0 0 1

1 1 0

0 1 1

1 0 1

1 1 1

black red green blue yellow cyan magenta white

True Color Display


24 bitplanes, 8 bits per color gun. 224 = 16,777,216

Green

Red

Blue

N

N

N

Color-Map Lookup Table


01000

011

67

100110100001

0

67

255

10011010 0001

R G B

RED

GREEN

BLUE

Pixel displayedat x', y'

Pixel inbit mapat x', y'

0 x0

y

xmax

maxy

Bit map Look-up table Display

extends the number of colors that can be displayed by a given number of bit-planes.

Fig. 4.LUT Video look-up table organization. A pixel with value 67 (binary 01000011) is displayed on the screen with the red electron gun at 9/15 of maximum, green at 10/15, and blue at 1/15. This look-up table is shown with 12 bits per entry. Up to 24 bits per entry are common.

Pseudo-Color: 28 x 24 Color Map LUT


0

1

2

3

254

255

RED GREEN BLUE

256 colors chosen from a palette of 16,777,216.

Each entry in the color map LUT can be user defined.

Could be used to define 256 shades of green or

64 shades each of red, blue, green and white,

etc.

Recall our generic CG box…..



ProcessorMemory

FramebufferVideo

Controller

PeripheralDevices

CPU SystemMemory

System Bus

Display Processor

©Larry F. Hodges, Zachary Wartell, K.R. Subramanian

Synonyms: Graphics Controller, Display Co-Processor, Graphics Accelerator, or GPU

Specialized hardware for rendering graphics primitives into the frame buffer.

b

a

Line(a,b)

a

b

Pixels: P0,0, P1,1, P2,2, P3,2, …. P7,7

Block-Pixel Copy(bitblt)

Scan-Conversion

Display Processor (2)


• Fundamental difference among display systems is how much the display processor does versus how much must be done by the graphics subroutine package executing on the general-purpose CPU.

NvidiaTM GTX 285(2009)GPU 1400M trans. 240 shader processors @ 1400Mhz1GB memory 21.4 B pix./sDisplay

Processor

CPUCPU

Video Controller


Cycles through the frame buffer, one scan line at a time. Contents of the memory are used the control the CRT's beam intensity or color.

X address

Y address

Pixel value(s)

Raster scan generator

Data

Horizontal and vertical deflection signals

Intensity or color

Linear address

Set or increment

Set or decrement

M e m o r y

Framebuffer

=

RAMDAC

Single Frame Buffer & Animation

Framebuffer

VideoController

GraphicsProcessor

problem with one object

problem with multiple objects

GraphicsProcessor

VideoController

©Zachary Wartell

(Front)

(Back)

(Back)

Double Buffer & Animation

GraphicsProcessor

VideoController

Frame Buffer 0

Frame Buffer 1(Front)

©Zachary Wartell

page flipping

Projectors


• Use bright CRT, LCD or DMD screens to generate an image which is sent through an optical system to focus on a (usually) large screen.

• Full color obtained by having separate monochromatic projector for each of the R,G,& B color channels

Advantages/Disadvantages of Projection Display


• Very large screens can provide large FoV and can be seen by several people simultaneously.

• Image quality can be fuzzy and somewhat dimmer than conventional displays.

• Sensitivity to ambient light.• Delicate optical alignment.

Displays in Virtual Reality


• Head-Mounted Displays (HMDs)– The display and a position tracker are

attached to the user’s head

• Head-Tracked Displays (HTDs)– Display is stationary, tracker tracks the

user’s head relative to the display.– Example: CAVE, Workbench, Stereo monitor

3D Display


binocular vision & stereopsis – a strong depth cue in physical world

3D Display – must generate at least two different images simultaneously, one per eye. The two images mimic the geometric differences seen in the physical world

volumetric display – pixels physically (or optically) spread over real 3D volume

stereoscopic display – two planar images. Optically channel left image to left eye and right image to right eye. Used in HMD, HTD, and regular displays.

-auto-stereoscopic versus wearing glasses

-commodity products available ($100 for LCD 3D glasses)

”wavefront” display – (in practice a hologram) a single planar display surface. Uses holographic optics to create full (omni-directional) wavefronts of light emanating from the virtual 3D world. [Interactive holography still in pure research phase – MIT, 3” partial-parallax hologram]

Before leaving displays, lets briefly discuss:

• Light

• Eye

- Physiology

- Functionality

• Color

- Perceptually based models

Color and Vision (Brief)

Light & Vision

© Kessler , Watson, Hodges, Ribarsky

• Vision is perception of electromagnetic energy (EM radiation).

• Humans can only perceive a very small portion of the EM spectrum:

Wavelength (nm)

Gamma X UV Infra Radar FM TV AM AC

Violet Blue Green Yellow Red 400 500 600 700

ciliary muscle

Eye Structure

• The eye can be viewed as a dynamic, biological camera: it has a lens, a focal length, and an equivalent of film.

• A simple diagram of the eye's structure:

retina

lens

cornea

© Wartell

suspensory ligments

iris

pupil

Eye: The Lens

• The lens must focus (accommodation) on directly on the retina for perfect vision:

• But age, genetic factors, malnutrition and disease can unfocus the eye, leading to near- and farsightedness:

FarsightedNearsighted


Eye: The Retina

• The retina functions as the eye's "film".

• It is covered with cells sensitive to light. These cells turn the light into electrochemical impulses that are sent to the brain.

• There are two types of cells, rods and cones


Retina

The Retina: Cell Distribution


20,000

100,000

60,000

180,000

140,000

cones

rods

Blind spot

Num

bers

of r

ods

or c

ones

pe

r m

m2

Temporal periphery

Fov

ea

Opt

ic d

isk

Nasal

periphery

(Right Eye)

20,000

100,000

60,000

180,000

140,000

cones

rods

Blind spot

Num

bers

of r

ods

or c

ones

pe

r m

m2

Temporal periphery

Fov

ea

Opt

ic d

isk

Nasal

periphery

(Right Eye)“Blind Spot Trick”

The Retina: Rods


• Sensitive to most visible frequencies (brightness).

• About 120 million in eye.

• Most located outside of fovea, or center of retina.

• Used in low light (theaters, night) environments, result in achromatic (b&w) vision.

• Absorption function:

400 700nm

The Retina: Cones


• R cones are sensitive to long wavelengths (nm), G to middle nm, and B to short nm.

• R: 64%, 32% G, 2% B• About 8 million in eye.• Highly concentrated in fovea, with B cones more

evenly distributed than the others (hence less in fovea).

• Used for high detail color vision (CRTs!), so they will concern us most.

The Retina: Cones


• The absorption functions of the cones are:

400 700

B G R445 nm 535 nm

575 nm

Color Constancy


• If color is just light of a certain wavelength, why does a yellow object always look yellow under different lighting (e.g. interior/exterior)?

• This is the phenomenon of color constancy.

• Colors are constant under different lighting because the brain responds to ratios between the R, G and B cones, and not magnitudes.

Vision: Metamers


• Because all colors are represented to the brain as ratios of three signals it is possible for different frequency combinations to appear as the same color. These combinations are called metamers. This is why RGB color works!

• Example – [Goldstein,pg143] mix 620nm red light with 530nm green light matches color percept of 580 nm yellow

BG

R

1.05.0 8.0

BG

R

1.05.0 8.0

530 + 620 580

Sensitivity vs Acuity


• Sensitivity is a measure of the dimmest light the eye can detect.

• Acuity is a measure of the smallest object the eye can see.

• These two capabilities are in competition.– In the fovea, cones are closely packed. Acuity

is at its highest, sensitivity is at its lowest (30 cycles per degree).

– Outside the fovea, acuity decreases rapidly. Sensitivity increases correspondingly.

Eye Versus 1280 x 1024 Display


28° 1280 pixel = 640 cycles

33 cm

Pictured: 22.8 c/d (cycles/degree_ with Vres=600/x → 26.25→ 20/26.25 vision (Snellen acuity)Widescreen at 60° → 20/56.25 vision

66 cm

Input Devices


Logical Devices

• Locator, to indicate a position and/or orientation

• Pick, to select a displayed entity

• Valuator, to input a single value in the space of real numbers

• Keyboard/String, to input a character string

• Choice, to select from a set of possible actions or choices

Locator Devices: Tablet, Mouse, Trackball, Joystick, Touch Panel, Light Pen

Keyboard devices: Alphanumeric keyboard (coded - get single ASCII character, unencoded - get state of all keys - more flexible)

Valuator Devices: Rotary dials (Bounded or Unbounded), Linear sliders

Choice Devices: Function keys

Locator Devices


degrees of freedom

2 DOF (mouse)

3 DOF (mouse+wheel), 3-space position tracker, mouse with rotation

6 DOF: 3-space position and orientation tracker

isotonic, isometric, elastic

controller order (differential mapping of physical to virtual movement)

0th order – position

1st order – velocity

2nd order – acceleration

SpaceballTM

Revisions

Revision 1.1 – updated slide 75 on metamers, updated eye diagram slide 68Revision 1.2 – added double buffer slides

Introduction to Computer Graphics: ITCS 4120/5120 Dr. Zachary Wartell Revision 1.2 2/16/07 Copyright...

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