overview of graphics system
TRANSCRIPT
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Overview of graphics system
Chapter 2
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Basic Graphics System
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Refresh Cathode-Ray Tube
Electron Gun
Focusing System
Horizontal Deflection
Plates
Vertical Deflection
Plates
Phosphor-Coated Screen
Electron Bean
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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
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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
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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
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Raster-Scan Display
The electron beam is swept across the screen, one row at
a time from top to bottom
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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
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Interlaced refresh
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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.
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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
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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.
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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
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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
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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
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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
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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
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Raster-Scan Systems
Architecture of a simple raster graphics system
CPUCPUSystem System
MemoryMemoryVideo Video
ControllerControllerMonitorMonitor
System BusSystem Bus
I/O Devices
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Graphics Process: Geometric Modeling
3D Geometric
Models
3D Geometric
Modelsrenderingrendering
3D Scanning
Interactive Geometric Modeling
Model Libraries
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Graphics Process: 3D Animation
3D Animation Definition
3D Animation Definition
renderingrendering
Model design
Motion Computation
Motion Capture
Dynamic Deformations
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Graphics Process:Texturing
Texture Information
Texture Information
renderingrendering
Scanned Images
Computed Images
Painted Images
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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
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Graphics Process: Image Storage and Display
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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)
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Coordinate Representations
Modeling Coordinates
World Coordinates
Normalized Coordinates