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TRANSCRIPT
Sun-Jeong Kim
Graphics Systems and Models
2nd Week, 2007
Computer Graphics Applications2
Graphics System
Five major elementsInput device
Processor
Memory
Frame buffer
Output device
A Graphics System
Computer Graphics Applications3
Input Devices
Most graphics systems provide a keyboard and at least one other input device
The mouse, the joystick, and the data tablet
To provide positional information to the system and signals to processor with one or more buttons
Spaceball
Mouse TrackballData Tablet
Joystick Lightpen
Computer Graphics Applications4
Pixels and the Frame Buffer (1)
Almost all graphics systems are raster based
RasterRasterAn array of pixelspixels (picture elements)
Frame bufferFrame bufferA part of memory where the pixels are stored
The core element of a graphics system
Pixels
Computer Graphics Applications5
Pixels and the Frame Buffer (2)
ResolutionResolutionThe number of pixels in the frame buffer
To determine the detail that you can see in the image
DepthDepth or precisionprecision of the frame bufferThe number of bits that are used for each pixel
To determine how many colors can be representedEx) 8 bits per pixel: 28=256 colors, 24 bits (true-color system)
RasterizationRasterization or scan conversionscan conversionConversion of geometric entities (such as lines, circles, and polygons) to pixel colors and locations in the frame buffer
Computer Graphics Applications6
Output Devices (1)
CRT (cathode-ray tube)Refresh rateRefresh rate
The same path is retraced by the beam at a sufficient high rate
Ex) 60 Hz (60 cycles per second)
TriadsTriadsTriangular group of three phosphors (red, green, and blue)
Shadow maskShadow mask
CRT Shadow-Mask CRT
Computer Graphics Applications7
Output Devices (2)
Flat-panel monitorsLight-emitting diodes (LEDs), liquid-crystal displays (LCDs), and plasma panels
Using a two-dimensional grid to address individual light-emitting elements
Projection systemsDigital light projection (DLP)
Hard-copy devicesPrinters and plotters
Generic Flat-Panel Display
Computer Graphics Applications8
Image Formation (1)
There always has been analogous process how image are formed by physical imaging systems
Cameras
Microscopes
Telescopes
Human visual systemRods and cones are light sensors
Rods – monochromatic, night vision
Cones – color sensitiveThree types of cones
Only three values (the tristimulus
values) are sent to the brain The Human Visual System
Computer Graphics Applications9
Image Formation (2)
Elements of image formationObjects
Independent of any viewer and
of any image-formation process
Viewer (camera)To form the image of objects
Light sourcesCamera System
Image Seen by Three Different Viewers
Computer Graphics Applications10
Light and Images
Interaction between light and the surfaces of the object How much light enters the camera
Light = visible spectrumvisible spectrumWavelengths in the range 350~780 nm
Long wavelengths: reds
Short wavelengths: blues
The Electromagnetic Spectrum
Computer Graphics Applications11
Imaging Models
Ray tracingRay tracingOne way to form an image
To follow rays of light from a point source finding which rays enter the lens of the camera
RadiosityRadiosityBased on conservation of energy
Ray Interactions
Computer Graphics Applications12
Imaging Systems
Pinhole camera
ProjectionProjection of point (x, y, z)
Field of viewField of view (angle of viewangle of view)
Pinhole Camera
Side View
Angle of View
dz
xxp −=
dz
yyp −= dzp −=
d
h
2tan2 2−=θ
Computer Graphics Applications13
Synthetic-Camera Model
Conceptual foundation for three-dimensional computer graphics
ProjectorProjectorLine from the center of lens to a point on the object
COPCOP (center of projectioncenter of projection)The center of the lens
Projection planeProjection planeVirtual image plane that are moved in front of the lens
Equivalent views of image formation
Synthetic Camera
Computer Graphics Applications14
Graphics Architectures
Graphics pipelineGeometryGeometry – collection of primitive types and vertices
Vertex processingWorld and view transformations
Projection
Lighting
Clipping and primitive assembly
Rasterization
Fragment processing
Geometric pipeline
Clipping