Overview of Graphics System

Overview of graphics system

Chapter 2

Basic Graphics System

Refresh Cathode-Ray Tube

Electron Gun

Focusing System

Horizontal Deflection

Plates

Vertical Deflection

Plates

Phosphor-Coated Screen

Electron Bean

Refresh Cathode-Ray Tube

o Focusing system o Electrostatic focusing o Positively charged metal cylinder

o Deflection of electron beam o Persistence

o How long phosphors continue to emit light o Low persistence is useful for animation

o Resolution o Number of points per centimeter can be

plotted horizontally and vertically

Refresh Cathode-Ray Tubeo Intensity distribution of a phosphor spot

o Adjacent spots appear distinct: 60% o Spot size also depends on intensity

o Deflection of electron beam o Resolution of a CRT depends

o Type of phosphor o Intensity to be displayed o Focusing and deflection system

o Aspect ratio o The ratio of vertical points to horizontal points

necessary to produce equal-length lines

Video Display Devices

o Raster-scan displays o Random-scan displays o Color CRT Monitors o Direct-view storage tubes o Flat-panel displays o Three-dimensional viewing devices o Stereoscopic and virtual-reality systems

Raster-Scan Display

The electron beam is swept across the screen, one row at

a time from top to bottom

Raster-Scan Displayo Frame buffer (refresh buffer)

Picture definition is stored in the memory areao Pixel Picture each screen point is referred as pixel or pelo Scan lineo Pixmap (bitmap) Picture for black-and-white system with o

ne bit per pixel, the frame buffer is called a bitmap. For systems with multiple bits per pixel the frame buffer is called a pixmap

o Refreshing (60 - 80 frames/sec) o Horizontal retrace o Vertical retrace o Interlacing each frame is displayed in two passo Scan conversion

Interlaced refresh

Random-Scan Display

A CRT has the electron beam directed only to the parts of the screen where the picture is to be drawndraw a picture one line.

Random-Scan Display

o Random-scan (vector, stroke-writing, calligraphic) displays o Draw a picture one line at a time

o Refresh rate o Depends on the number of lines to be displayed

o Picture definition o A set of line-drawing commands o Refresh display file

o Designed for line drawing applicationso Can not display realistic shaded scenes

Color CRT Monitors

o Beam-penetration method o Used with random-scan monitorso Two layers of phosphor: red and green o The displayed color depends on how far the electron

beam penetrates into the phosphor layers. o Only four colors are possible: red, green, orange, and

yellow.

Color CRT Monitors

o Shadow-mask method o Three phosphor color dots at each pixel position o Three electron guns o Color variations: Varying the intensity levels of the

three electron beams o Full-color (true-color) system: 24 bits of storage per

pixel

Direct-View Storage Tubes

o Store the picture information inside the CRT o A charge distribution just behind the phosphor-

coated screen o Two electron guns: primary gun and flood gun

o Advantage o Very complex pictures can be displayed at very high

resolutions

o Disadvantages o Do not display color o Selected parts of a picture cannot be erased

Flat-Panel Displays

o Video devices have reduced o volume, o weight, and o power requirements

o compared to a CRT. o A significant feature - thinner than CRT o Classified into two categories:

o Emissive displays o Nonemissive displays

Three-Dimensional Viewing Devices

o Three-dimensional display system o Reflects a CRT image from a vibrating, varifocal mirror. o The mirror changes focal length to match the depth of poi

nts in a scene. o Genisco SpaceGraph System

o Project objects into a 25X25 X25 cm3 volume o Applications

o Medical o Geological o Molecules

Stereoscopic and Virtual-Reality Systems

o Stereoscopic view o Present a different view to each eye of an

observer o Need to obtain two views (left and right) of

a scene o Shutter glasses o Infrared synchronizing emitter

o Head-mounted displays o Two LCD displays o Tracking devices o Earphone

Raster-Scan Systems

Architecture of a simple raster graphics system

CPUCPUSystem System

MemoryMemoryVideo Video

ControllerControllerMonitorMonitor

System BusSystem Bus

I/O Devices

Raster-Scan Systems

A fixed area of system reserved for frame buffer

CPUCPUSystem System

MemoryMemoryVideo Video

ControllerControllerMonitorMonitor

System BusSystem Bus

I/O Devices

Frame Frame bufferbuffer

Video Controllero Coordinate system

o Frame-buffer locations are referenced in Cartesian coordinates.

o Coordinate origin o Lower left screen corner o Upper left screen corner

o Refresh operations of video controller o Top-to-bottom, left-to right o x register ( initial value = 0) o y register (initial value = ymax)

Video Controller

Raster-scan GeneratorRaster-scan Generator

X X RegisterRegister

Pixel Pixel RegisterRegister

Frame BufferFrame Buffer

Y Y RegisterRegister

Memory AddressMemory Address

Horizontal and Vertical Deflection Voltages

Intensity

Raster-Scan Display Processor

o Display processor (graphics controller, display coprocessor) o To free the CPU from the graphics chores o Digitize a picture definition into a set of

pixel-intensity values o Scan conversion: The digitization process

is called. o Straight-line segments o Curved lines and polygon outlines o Characters

Raster-Scan Display Processor

CPUCPUDisplay Display

ProcessorProcessor

Video Video ControllerController

MonitorMonitor

System BusSystem Bus

I/O Devices

System System MemoryMemory

Display Processor Display Processor MemoryMemory

Frame Frame bufferbuffer

Raster-Scan Display Processor

o Display processor functions o Generating various line styles o Displaying color areas o Performing certain transformations o Manipulations on display objects

o Run-length encoding o Reduce memory requirements o Organizing the frame buffer as a linked list o Store a scan line as a set of integer pairs

o An intensity value o The number of adjacent pixels with the same intensity

Random-Scan SystemsGraphics commands are translated into a display file stored in the system memory

CPUCPUSystem System

MemoryMemoryDisplay Display

ProcessorProcessorMonitorMonitor

System BusSystem Bus

I/O Devices

Advanced 3D Graphics Architecture

Object DatabaseObject

Database

Geometric Transformation

Engine

Geometric Transformation

Engine

Clipping perspective

scaling

Clipping perspective

scaling

Lighting Model

Calculator

Lighting Model

Calculator

Shading Rasterizer

Shading Rasterizer

Frame buffer

Video Controler

Video Controler

Input/Output Devices

o Input Devices o Keyboards o Mouse/3D mouse o Digitizer o Trackball and Spaceba

llo Joystickso Image scanner o Data Glove o Touch panelso Light pens

o Output Devices o Color graphics

display/Head mounted display

o Photo-realistic color printer o Film recorder o Video output (Video tape,

LD recorder)o Pen plotter

Graphics Software

o Classificationo General programming packageo Special-purpose applications package

o Standards Independent of any languageo GKS - Graphics Kernel System (ISO) o PHIGS - Programmer’s Hierarchical Interactive

Graphics Standard (extension of GKS) PHIGS+o Language Binding defined for particular programming

languageo OpenGL SGI (Silicon Graphics Inc.) o Direct 3D Microsofto Animation Packages

o ALIAS/WAVEFRONT (SGI) o 3D Studio Max o Maya

o VR Packages o Division o Sense 8 o VRML

Graphics Process: Overview

3D Geometric Models

3D Geometric Models

renderingrendering

Texture InformationTexture

Information

Image Storage and Display

Image Storage and Display

3D animation definition

3D animation definition

Graphics Process: Geometric Modeling

3D Geometric

Models

3D Geometric

Modelsrenderingrendering

3D Scanning

Interactive Geometric Modeling

Model Libraries

Graphics Process: 3D Animation

3D Animation Definition

3D Animation Definition

renderingrendering

Model design

Motion Computation

Motion Capture

Dynamic Deformations

Graphics Process:Texturing

Texture Information

Texture Information

renderingrendering

Scanned Images

Computed Images

Painted Images

Graphics Process: Rendering

3D Geometric Models

3D Geometric Models

Texture InformationTexture

Information

Image Storage and Display

Image Storage and Display

3D animation definition

3D animation definition

rendering

Transformation Clipping

Perspective

Image Generation

Graphics Process: Image Storage and Display

Coordinate Representations

o Modeling coordinates: (xmc, ymc, zmc) o Any floating-point values

o World coordinates: (xwc, ywc, zwc) o Any floating-point values

o Normalized coordinates: (xnc, ync, znc) o 0 < xnc < 1, 0 < ync < 1, 0 < znc < 1

o Device coordinates: (xdc, ydc) o Integers within the range (0,0) to (xmax, ymax)

Coordinate Representations

Modeling Coordinates

World Coordinates

Normalized Coordinates