1. Computer Graphics
Introduction

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Introduction
Computer Graphics : It involves display manipulation and storage of pictures and experimental data for proper visualization using a computer.
Typically graphics system comprises of the host computers with support of
fast processor,
large memory,
frame buffer
display devices,
input devices,
output devices
interface devices.
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3. Conceptual Framework for Interactive Graphics
Application Model
Application Program
Graphics System
Input Devices
Output devices
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4. Typical Application Areas
GUI
Plotting in business
Office Automation
Desktop Publishing
Plotting in Science and Technology
Web/Commercial/Business publishing and advertisements
CAD/CAM Design(VLSI, Construction, Circuits)
Scientific visualization
Entertainment
Simulation and Simulation Study
Cartography
Multimedia
Virtual reality
Process monitoring
Digital Image processing
Education and Training
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5. GUI – Graphics User Interface
Typical Component used-
Menus
Icons
Cursors
Dialog Boxes
Scroll Bars
Buttons
Valuators
Grids
3-D Interfaces
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Application Packages
Various application package and standards available
Core Graphics
GKS
SRGP
PHIGS, SPHIGS and PEX 3D
OpenGL(With ActiveX and Direct3D)
X11 Based Systems
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GKS- Graphics Kernel System
Developed by ISO and ANSI
SRGP- Simple Raster Graphics Package
PHIGS- Programmers Hierarchical Intaractive Graphics Systems
Various tools and utilities available for web based design include – JAVA, XML, VRML and GIF Animators
Certain compilers with their own graphics libraries, API support and help for programming 2D/3D graphics.
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Display
A graphics display is a drawing area comprised of an array of fine points called pixels (picture elements).
At the heart of a graphics system there is a magic pen,
move at lightning speed to a specific pixel
draw the pixel with a specific color — a red, green, and blue (RGB) vector value.
Computer graphics is about using this pen automatically through programming.
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Object, Model, and Image
A real or imaginary object is represented in a computer as a model, and is displayed as an image.
A model is an abstract description of the object’s shape (vertices) and attributes (colors),
which can be used to find all the points on the object corresponding to the pixels in the drawing area.
Given a model, the application program will control the pen through a graphics library to generate the corresponding image.
An image is simply a 2D array of pixels.
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10. Primitive and Graphics Library
A graphics library provides a set of graphics commands or functions.
bound in C, Java, or other programming languages on different platforms.
specify primitive 2D and 3D geometric models to be digitized and displayed.
Primitive models or simply primitives stand for some simple shapes (such as points, lines, and polygons)
OpenGL is a graphics library; DirectX includes a graphics library Direct3D
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Brief History
1963 Evan Sutherland’s seminal doctoral work “Sketchpad: a man-machine graphical communication system”
1977 3D Core Graphics System by ACM SIGGRAPH Committee
1980’s, hardware expensive & graphics app. programs were few
1985 GKS (the Graphical Kernel System), 2D
1987 MIT’s X lib for windows under UNIX OS
1988 GKS-3D, PHIGS (ANSI and ISO standard); SGI’s GL;
1993 OpenGL (Open standard from SGI)
Since then, OpenGL supported on PC, MAC, Sun work-stations, SGI work-stations, special purpose image generators (ESIG)
Since then, Evolution of advanced GUI’s and graphics environments; Software from low-level, device dependent packages to higher-level device-independent packages
2003 JOGL – Java for OpenGL from Sunmicrosystem
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Cathode Ray Tube (CRT)
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Color CRT
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Type of CRT Display Devices
DVST (Direct View Storage Tube)
Calligraphic or Random Scan Display System
Refresh and Raster Scan Display System
DVST(Direct View Storage Tube)
Storage Tube – It is a CRT with a long persistence phosphor
Provides Flicker – Free Display
No refreshing necessary
A slow moving electron beam draws a line on the screen.
Screen has a storage mesh in which the phosphor is embedded.
Image is stored as a distribution of charges on the inside surface of the screen.
Limited interactive support.
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19. Phosphor Coated Screen
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DVST- Drawbacks
Modifying any part of the image requires redrawing the entire image.
Change in the image requires to generate new charge distribution in the DVST.
Slow process of drawing- typically a few seconds are necessary for a complex image.
Erasing takes approx. 0.5 second. All lines and character must be erased.
No animation possible with DVST.
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21. Calligraphic or Random Scan Display System
Also called vector , stroke, line drawing displays.
Characters are also made of sequence of strokes (or short lines)
Vectored – Electron beam deflected from end- point to end-point.
Random Scan - Order of deflection is dictated by the arbitrary order of the display commands.
Phosphor has short persistence – delay in micro seconds
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22. Calligraphic or Random Scan Display System
Display must be refreshed at regular interval minimum of 30 Hz(fps) for flicker free display.
Refresh Buffer- Memory space allocated to store the display list or display program for the display processor to draw the image.
The display processor interprets the commands in the refresh buffer for plotting.
The display processor must cycle through the display list to refresh the phosphor.
Display program has the commands for point, line and character plotting.
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23. Conceptual Block Diagram Calligraphic Refresh Display I
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24. Conceptual Block Diagram Calligraphic Refresh Display II
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25. Calligraphic or Random Scan Display System
The Display processor sends digital and point coordinate values to the vector display.
The vector generator converts the digital coordinate values to analog voltages for the beam deflection circuits.
The Beam deflection circuits displays the electron beam for writing on the CRT’s phosphor coating.
Recommended refresh rate is Hz.
Scope of animation with segmentation mixture of static and dynamic parts of the picture.
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RASTER DISPLAYS
Store the primitives in a famebuffer, or refresh buffer which is RAM with 1024*1280, or V*H addressable pixels.
Bitmap – array of 1/0 (pixels)
Pixmap- array of gray-scale pixels
Monocrome – Bi-level
Gray Scale – multiple level(1-15)
Color – (R,G,B)
Scan-Conversion(rasterization ) – Objects are converted into discrete pixels in frame buffer.
Aliasing – Jagging or Stair casing of lines/ edges
Anti-Aliasing - Dealing with aliasing
Resolution - # of distingushable lines per inch
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CRT (CATHODE RAY TUBE)
LASER PRINTER (HARD COPY DISPLAY DEVICE)
Framebuffer
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RASTER DISPLAY SYSTEMS
Graphics card:
handle scan-conversion and other advanced graphics functions
Graphics Card (Video Card)
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Frame Buffer(Bit Planes) : RAM with the generated pixmap and attribute ready to display.
Video Controller : refresh the display.
Interlacing (bitmaps), a method of incrementally displaying raster graphics
Interlaced: fine as long as adjacent scan lines display similar information
# of bits for color : Direct(RGB Mode) and indirect(Index Mode)
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Interlacing
A method of encoding a bitmap image such that a person who has partially received it sees a degraded copy of the entire image.
When communicating over a slow communications link, this is often preferable.
Interlacing is supported by the following formats, where it is optional:
GIF interlacing stores the lines in the order 0, 8, 16, ...(8n), 4, 12, ...(8n+4), 2, 6, 10, 14, ...(4n+2), 1, 3, 5, 7, 9, ...(2n+1).
PNG uses the Adam7 algorithm, which interlaces in both the vertical and horizontal direction.
JPEG, JPEG 2000, and JPEG XR (actually using a frequency decomposition hierarchy rather than interlacing of pixel values)
PGF (also using a frequency decomposition)
Interlacing is also known as "progressive" encoding, because the image becomes progressively clearer as it is received. This terminology is different than the interlaced and progressive scan terminology of video encoding.
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