Computer Graphics Introduction
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. 1/13/2011 2
Conceptual Framework for Interactive Graphics Input Devices Application Model Application Program Graphics System Output devices 1/13/2011 3
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 1/13/2011 4
GUI Graphics User Interface Typical Component used- Menus Icons Cursors Dialog Boxes Scroll Bars Buttons Valuators Grids 3-D Interfaces 1/13/2011 5
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 1/13/2011 6
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. 1/13/2011 7
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. 1/13/2011 8
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. 1/13/2011 9
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 1/13/2011 10
Brief History 1963 Evan Sutherland s seminal doctoral work Sketchpad: a manmachine 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 1/13/2011 11
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Cathode Ray Tube (CRT) 1/13/2011 13
Color CRT 1/13/2011 14
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Type of CRT Display Devices 1. DVST (Direct View Storage Tube) 2. Calligraphic or Random Scan Display System 3. Refresh and Raster Scan Display System DVST(Direct View Storage Tube) 1. Storage Tube It is a CRT with a long persistence phosphor 2. Provides Flicker Free Display 3. No refreshing necessary 4. A slow moving electron beam draws a line on the screen. 5. Screen has a storage mesh in which the phosphor is embedded. 6. Image is stored as a distribution of charges on the inside surface of the screen. 7. Limited interactive support. 1/13/2011 17
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Phosphor Coated Screen 1/13/2011 19
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. 1/13/2011 20
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 endpoint. Random Scan - Order of deflection is dictated by the arbitrary order of the display commands. Phosphor has short persistence delay in 10-100 micro seconds 1/13/2011 21
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. 1/13/2011 22
Conceptual Block Diagram Calligraphic Refresh Display I 1/13/2011 23
Conceptual Block Diagram Calligraphic Refresh Display II 1/13/2011 24
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 40-50 Hz. Scope of animation with segmentation mixture of static and dynamic parts of the picture. 1/13/2011 25
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 1/13/2011 26
LASER PRINTER (HARD COPY DISPLAY DEVICE) CRT (CATHODE RAY TUBE) Framebuffer 1/13/2011 27
RASTER DISPLAY SYSTEMS Graphics Card (Video Card) Graphics card: handle scan-conversion and other advanced graphics functions 1/13/2011 28
Frame Buffer(Bit Planes) : RAM with the generated pixmap and attribute ready to display. Video Controller : refresh the display. Interlaced: fine as long as adjacent scan lines display similar information # of bits for color : Direct(RGB Mode) and indirect(index Mode) 1/13/2011 29
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