1EEL 5771-001

Introduction to Computer Graphics

PPT1: PRINCIPLES OF COMPUTER GRAPHICS

PRESENTED BY

AKHIL SURABHI

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Display Devices

• A Cathode Ray Tube(CRT) is an electronic tube designed to display the electrical data.

• The basic cathode ray tube consists of four major components namely:Electron GunFocusing anodesHorizontal and vertical deflection platesEvacuated glass tube

• Cathode-ray tube (CRT) architecture

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Display Devices

• CRT FOCUSING & DEFLECTION SYSTEMS: An electron beam produced by an electron gun would have a tendency to spread out In order to form a cone shaped beam. However, the beam that strikes the display screen must be pencil thin and clearly defined. In order to form the electronic beam into correct shape, an electrical or magnetic lens is created.

• There are two kinds of systems available for controlling the path of the electron beam, with a electrostatic system and a magnetic system. In either of the cases, both the

deflections are needed , one to move the beam in the horizontal direction and one to move in the vertical direction.

• PHOSPHOR TYPES: There are various types in phosphor available. Brightness, color and persistence of the illumination depends upon the type of the phosphor used in the CRT screen. Phosphors ranging from less than one microsecond to several seconds. We can briefly categorize it into long persistence phosphor and short persistence phosphor.

• HOW LIGHT IS GENERATED ON SCREEN: A cathode ray tube consists of a vacuum tube that contains

one or more electron guns to excite phosphors on a screen to produce images. The phosphors in CRT ‘s screen are the materials that directly produce photons generated by CRT. These phosphors are struck by incoming electrons from the electron gun, absorb energy and then re-

emitsome or all of that energy in the form of light.

Display Devices 4

• Fluorescence: It is the light emitted when the unstable electrons loose their excess energy while the phosphor is being struck by electrons

• Phosphorescence: is the light given off by the return of the relatively more stable excited electrons to their unexcited state once the electron beam excitation is removed.

• Persistence: It is the time for removal of excitation to the moment when phosphorescence has decayed to 10 percent of the initial light output

• Flicker: This is developed when the eye can no longer integrate the individual light impulses coming from a pixel.

• Refresh rate: A refresh rate in CRT is number of times per second the image is redrawn which is typically 60 times per second for raster displays.

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Display Devices

• Resolution (vertical/horizontal): The resolution is the distance between the two outermost lines divided by the number of lines in a raster. There is a clear dependence between the spot size and achievable resolution.

• Pixel energy distribution function.

• Horizontal scan rate: It is the number of scan lines per second that the circuitry driving a CRT is able to display. The rate is approximately the product of the refresh rate and the number of scan lines. For a given scan rate, an increase in the refresh rate means a decrease in the number of scan lines.

• Bandwidth: The bandwidth of the monitor has to do with which the electron gun can be

turned on or off.

• Picture storage: These are found in analog storage oscilloscopes, which are distinct from solid state digital memory to store the image.

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Display Devices

• Horizontal/vertical trace: The CRT display is divided into grids by vertical and horizontal lines. It is important for accurate measurements, that the trace be perfectly for horizontal.

• Interlacing: It is to produce a picture whose effective refresh rate is closer to 60 than to 30Hz. This technique works as long as adjacent scan lines do in fact display similar information, an image consisting of horizontal lines on alternating scan lines would flicker.

• Picture storage for color and B&W imaged: These are found in analog storage

oscilloscopes, which are distinct from solid state digital memory to store the image.

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Display Devices

• Color displays: The LCs is an alternative to shadow mask CRT, but has the limited color resolution. This technology is extended to work with three colors.

• Delta-delta CRTs:

Three guns and phosphor dots are arranged in triangular (delta) pattern, where the shadow mask allows the electrons from each gun to hit only the corresponding phosphor dots.

• Vector displays: It flickers when the number of primitives in the buffer becomes too large, typically a maximum of a few hundred thousand short vectors.

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Raster-Scan Systems

• Architecture of raster scan systems

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Raster-Scan Systems

• Refresh operation from frame buffer:

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GPU PowerGPU Power

• Architecture of the GPU:

• Applications of the GPU: 1) GPU cluster2) Mathematica includes built-in support for CUDA and OpenGL GPU execution.3) MATLAB acceleration4) Molecular modeling on GPU

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Graphics Workstations

• Graphics work stations: A workstation specially configured for graphics works such as image manipulation, bitmap graphics applications. Such work requires powerful CPU and a higher resolution display.

A Graphics workstation is very similar to a CAD workstation and given the typical specifications of personal computers currently available in 1999. The distinctions are very blurred and are more likely to depend on availability of specific software than any detailed hardware requirements.

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Graphical Input

• Graphics input devices1) Mouse2) Track ball3) Light pen4) Data tablet5) Joystick6) Space ball

• Principles of 2D and 3D input devices

The present invention relates to a three-dimensional input device which allows a user to enter all six degrees of freedom, three translational coordinates and three rotational coordinates, simply, independently, and in an intuitive manner.

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Input Devices

• Graphics input devices– Keyboard– Mouse– Function dials– Joystick– Graphics tablet

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Input Devices

• Polhemus device: Polhemus technology delivers full 6DOF motion tracking, measuring both position and orientation, and our proprietary AC electro magnetic technology requires no line-of-sight. Because of this, our sensors have the capability to be embeddable, and our motion trackers are the clear choice for the leaders in healthcare simulation, including ultra sound simulators.

• Data glove: A data glove also called as a wired glove is an input device for human computer interaction worn like a glove.

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Input Devices

• Digitizing: It is a representation of object, image, sound and document or a signal by a discrete set of points or samples. This representation is called digital representation or more specifically a digital image for the object and digital form for the signal.

• Scanner types:1) Flatbed scanners: Bundled with Adobe Photoshop • Entry level• Mid-level• High level2) Transparency scanners: Used in scanning thinnest of images3) Handheld scanners: used for their probability and low price4) Drum scanners: used for producing color separations for high-end printing

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Input Devices

• Principles of touch panels: A touch screen is an input device normally layered on the top of an electronic and visual display of an information processing system. A user can give input or control the information processing system through simple or multi-touch gestures by touching the screen with a special pen and or with one or more fingers

• Optical touch panel: It is relatively modern development in touchscreen technology, in which two or more image sensors are placed around the edges (mostly the corners) of the screen. Infrared back lights are placed in the camera's field of view on the other side of the screen

17• Electric touch panels: The touch sensitive surface is an extremely durable and flexible glass

or polymer touch response surface

• Acoustical touch panels:

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Input Devices

• Light pen: A light pen is a computer input device in the form of alight-sensitive wand used in conjunction with a computer's CRT display. It allows the user to point to displayed objects or draw on the screen in a similar way to a touchscreen but with greater positional accuracy.

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Voice recognizer: In computer science and electrical engineering, speech recognition is the of spoken words into text. It is also known as “Automated speech recognition”.

Input Devices

20Hard-Copy Devices

• Hard copy devices: In information handling, a hardcopy is a permanent reproduction or a copy in the form of a physical object, of any media suitable for direct use by a person, of displayed transmitted data.

– Dot matrix printer: Dot matrix printing or impact matrix printing is a type of computer printing which uses a print head that moves back and forth, or in an up and down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a typewriter.

– Laser printer: A non-impact high-resolution printer which uses a rotating disk to reflect laser beams to form an electrostatic image on a selenium imaging drum. The developer drum transfers toner from the toner bin to the charged areas of the imaging drum, which then transfers it onto the paper into which it is fused by heat.

Hard-Copy Devices 21

⁻ Ink-jet printer: a high-speed typing or printing process in which charged droplets of ink issuing from nozzles are directed onto paper under computer control.

⁻ Electrostatic printer: A process (such as xerography) for printing or copying in which electrostatic forces are used to form the image (as with powder or ink) directly on a surface.

⁻ Thermal printer: Thermal printing (or direct thermal printing) is a digital printing process which produces a printed image by selectively heating coated thermal paper as it is commonly known, when the paper passes over the thermal print head.

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Hard-Copy Devices

• Principles of 3D printing: 1. Manufacturing complexity is free2. Variety is free3. No assembly required4. Zero lead time5. Unlimited design space6. Zero skill manufacturing7. Compact, portable manufacturing8. Less waste by product9. Infinite shades of materials

• Types of 3D printers:1. Stereo lithography(SLA)2. Fused deposition modeling (FDM)3. Selective Laser Sintering (SLS)4. Selective laser melting (SLM)5. Electronic Beam Melting (EBM)6. Laminated object manufacturing (LOM)

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Graphics Software

• Overview of graphics software systems:There are two broad classifications for computer-graphics software: special purpose packages

and general programming packages. Special-purpose packages are designed for nonprogrammers who want to generate pictures, graphs, or charts in some application area without worrying about the graphics procedures that might be needed to produce such displays. The interface to a special purpose package is typically a set of menus that allows users to communicate with the programs in their own terms. Examples of such applications include artist’s painting programs and various architectural, business, medical, and engineering CAD systems. By contrast, a general programming package provides a library of graphics functions that can be used in a programming language such as C, C++, Java, or Fortran.

• Various coordinate systems:To generate a picture using a programming package, we first need to give the geometric

descriptions of the objects that are to be displayed. These descriptions determine the locations and shapes of the objects. If coordinate values for a picture are given in some other reference frame (spherical, hyperbolic, etc.), they must be converted to Cartesian coordinates before they can be input to the graphics package.

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Graphics Software

• Types of graphics functions:A general-purpose graphics package provides users with a variety of functions for creating and

manipulating pictures. These routines can be broadly classified according to whether they deal with graphics output, input, attributes, transformations, viewing, subdividing pictures, or general control.

Interactive graphics applications make use of various kinds of input devices, including a mouse, a tablet, or a joystick. Input functions are used to control and process the data flow from these interactive devices. The following are the types of graphic functions:

– Control functions– I/O functions– Modeling functions– Viewing transformations– Attributes selection– Object rendering– Output primitives

25Sample Program

•A sample graphics program in any language (OpenGL is recommended):•The following code defines a two-dimensional, straight-line segment with integer, Cartesian endpoint coordinates (180, 15) and (10, 145)#include // (or others, depending on the system in use) void init (void) { glClearColor (1.0, 1.0, 1.0, 0.0); // Set display-window color to white. glMatrixMode (GL_PROJECTION); // Set projection parameters. gluOrtho2D (0.0, 200.0, 0.0, 150.0); }void lineSegment (void) {glClear (GL_COLOR_BUFFER_BIT); // Clear display window. glColor3f (1.0, 0.0, 0.0); // Set line segment color to red. glBegin (GL_LINES); glVertex2i (180, 15); // Specify line-segment geometry. glVertex2i (10, 145); •glEnd ( ); •glFlush ( ); // Process all OpenGL routines as quickly as possible.

26} void main (int argc, char** argv) { glutInit (&argc, argv); // Initialize GLUT. glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); // Set display mode. glutInitWindowPosition (50, 100); // Set top-left display-window position. glutInit (&argc, argv); // Initialize GLUT. glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); // Set display mode. glutInitWindowPosition (50, 100); // Set top-left display-window position. glutInitWindowSize (400, 300); // Set display-window width and height. glutCreateWindow ("An Example OpenGL Program"); // Create display window. init(); // Execute initialization procedure. glutDisplayFunc (lineSegment); // Send graphics to display window. glutMainLoop ( ); // Display everything and wait. }

Sample Program

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REFERENCES

http://www.cs.utexas.edu/~fussell/courses/cs324e2003/hear50265_ch02.pdf

https://en.wikipedia.org/wiki/Cathode_ray_tube

http://www.moreprocess.com/devices/architecture-and-working-of-a-cathode-ray-tube-crt

https://reference.wolfram.com/language/ref/ComputerGraphics.html

http://overunity.com/