CU-BCA-SEM-IV-Computer Graphics_Second Draft

BACHELOR OF COMPUTER APPLICATIONS SEMESTER-IV COMPUTER GRAPHICS

CHANDIGARH UNIVERSITY Institute of Distance and Online Learning SLM Development Committee Prof. (Dr.) H.B. Raghvendra Vice- Chancellor, Chandigarh University, Gharuan, Punjab:Chairperson Prof. (Dr.) S.S. Sehgal Registrar Prof. (Dr.) B. Priestly Shan Dean of Academic Affairs Dr. Nitya Prakash Director – IDOL Dr. Gurpreet Singh Associate Director –IDOL Advisors& Members of CIQA –IDOL Prof. (Dr.) Bharat Bhushan, Director – IGNOU Prof. (Dr.) Majulika Srivastava, Director – CIQA, IGNOU Editorial Committee Prof. (Dr) Nilesh Arora Dr. Ashita Chadha University School of Business University Institute of Liberal Arts Dr. Inderpreet Kaur Prof. Manish University Institute of Teacher Training & University Institute of Tourism & Hotel Management Research Dr. Manisha Malhotra Dr. Nitin Pathak University Institute of Computing University School of Business © No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any formor by any means, electronic, mechanical, photocopying, recording and/or otherwise without the prior written permission of the authors and the publisher. SLM SPECIALLY PREPARED FOR CU IDOL STUDENTS 2 CU IDOL SELF LEARNING MATERIAL (SLM)

First Published in 2021 All rights reserved. No Part of this book may be reproduced or transmitted, in any form or by any means, without permission in writing from Chandigarh University. Any person who does any unauthorized act in relation to this book may be liable to criminal prosecution and civil claims for damages. This book is meant for educational and learning purpose. The authors of the book has/have taken all reasonable care to ensure that the contents of the book do not violate any existing copyright or other intellectual property rights of any person in any manner whatsoever. In the event, Authors has/ have been unable to track any source and if any copyright has been inadvertently infringed, please notify the publisher in writing for corrective action. 3 CU IDOL SELF LEARNING MATERIAL (SLM)

CONTENT Unit - 1 Introduction.............................................................................................................. 5 Unit – 2 Video Display Devices Part I................................................................................. 16 Unit – 3 Video Display Devices Part II................................................................................ 37 Unit - 4 Two-Dimensional Graphics Primitives Part I.......................................................... 67 Unit - 5 Two-Dimensional Graphics Primitives Part II ........................................................ 77 Unit - 6 Two-Dimensional Graphics Primitives Part III ....................................................... 95 Unit - 7 Two-Dimensional Viewing .................................................................................. 122 Unit – 8 Two-Dimensional Geometric Transformations Part I ........................................... 138 Unit- 9 Two-Dimensional Geometric Transformations Part II ........................................... 150 Unit - 10 Three-Dimensional Transformations Part I......................................................... 163 Unit - 11 Three-Dimensional Transformations Part II........................................................ 178 Unit - 12 Three-Dimensional Transformations Part III ...................................................... 187 Unit 13 – Three Dimensions Viewing ............................................................................... 208 4 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT - 1INTRODUCTION STRUCTURE 1.0 Learning Objectives 1.1 Introduction 1.2 Computer Graphics 1.2.1 Introduction to Image and Objects 1.2.2 Basic Graphics Pipeline 1.2.3 Bitmap and Vector-Based Graphics 1.3 Applications 1.4 Summary 1.5 Keywords 1.6 Learning Activity 1.7 Unit End Questions 1.8 References 1.0LEARNING OBJECTIVES After studying this unit, you will be able to:  Comprehend the basics of computer graphics.  Differentiate between images and objects.  Elucidate the basic graphics pipeline.  Differentiate between bitmap and vector-based graphics.  Explain the applications of computer graphics. 1.1INTRODUCTION Graphics is defined as any sketch or a drawing or a special network that pictorially represents some meaningful information. Computer graphics deals with generating images with the aid of computers. The term computer graphics has been used in a broad sense to describe \"almost everything on computers that is not text or sound\". Origin of Computer Graphics Years of research and development were made to achieve the goals in the field of computer graphics. In 1950 the first computer driven display was used to generate only simple pictures. 5 CU IDOL SELF LEARNING MATERIAL (SLM)

This display made use of a cathode ray tube similar to the one used in television sets. During 1950’s interactive computer graphics made little progress because the computers of that period were so unsuited to interactive use. These computers were used to perform only lengthy calculations. By the mid -1960’s large computer graphics research projects were under taken at MIT, Bell Telephone Labs and General Motors. Thus, the golden age of computer graphics began. In 1970’s the researches began to bear fruit. What Does it Involve? Computer graphics involves display, manipulation and storage of pictures and experimental data for proper visualization using a computer. It provides methods for producing images and animations (sequence of images). It deals with the hardware as well as software support for generating images. Basically, there are four major operations that we perform in computer graphics:  Imaging: refers to the representation of 2D images.  Modelling: refers to the representation of 3D images.  Rendering: refers to the generation of 2D images from 3D models.  Animation: refers to the simulation of sequence of images over Different Types of Computer Graphics Computer Graphics can be broadly divided into two types, as follows: 1. Non-Interactive Computer Graphics Otherwise known as passive computer graphics, the observer has no control over the image. Familiar examples of this type of computer graphics include the titles shown on TV and other forms of computer art. 2. Interactive Computer Graphics Interactive Computer Graphics involves a two-way communication between computer and user.Here the observer is given some control over the image by providing him/her with an input device for example the video game controller. This helps him/her to signal his request to the computer. The computer on receiving signals from the input device can modify the displayed picture appropriately. To the user it appears that the picture is changing instantaneously in response to his commands. He/She can give a series of commands, each one generating a graphical response from the computer. In this way he maintains a conversation, or dialogue, with the computer. Computer Graphics can be used in digital photography, film, entertainment, electronic gadgets and all other core technologies which are required. It is a vast subject and area in the field of computer science. In most areas, computer graphics is an abbreviation of CG. There are several tools used for implementation of Computer Graphics. 6 CU IDOL SELF LEARNING MATERIAL (SLM)

1.2 COMPUTER GRAPHICS An image is basically representation of a real-world object on a computer. It can be an actual picture display, a stored page in a video memory, or a source code generated by a program. Mathematically, an image is a two - dimensional array of data with intensity or a colour value at each element of the array. Objects are real world entities defined in three – dimensional world coordinates. 1.2.1 Introduction to Image and Objects In computer graphics we deal with both 2D and 3D descriptions of an object. We also study the algorithms and procedures for generation and manipulation of objects and images in computer graphics. Image Representation Image representation is the approximations of the real world displayed in a computer. A picture in computer graphics is represented as a collection of discrete picture elements termed as pixels. A pixel is the smallest element of picture or object that can be represented on the screen of a device like computer 1.2.2 Basic Graphics Pipeline In computer graphics, the graphics pipeline refers to a series of interconnected stages through which data and commands related to a scene go through during rendering process. It takes us from the mathematical description of an object to its representation on the device. The figure shown below illustrates a 3D graphic pipeline 7 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 1.1: A 3D graphic pipeline The real-world objects are represented in world coordinate system. It is then projected onto a view plane. The projection is done from the viewpoint of the position of a camera or eye. There is an associated camera coordinate system whose z axis specifies the view direction when viewed from the viewpoint. The infinite volume swept by the rays emerging from the viewpoint and passing through the window is called as view volume or view pyramid. Clipping planes (near and far) are used to limit the output of the object. The mapping of an object to a graphic device requires the transformation of view plane coordinates to physical device coordinates. There are two steps involved in this process. i. The window to a viewport transformation. The viewport is basically a sub – rectangle of a fixed rectangle known as logical screen. ii. The transformation of logical screen coordinates to physical device coordinates The figures below depict the graphic pipeline and the 2D coordinate transformation to physical device coordinates. Figure 1.2: Sequence of transformation in viewing pipeline Figure 1.3: 2D coordinate system to physical device coordinates transformation. 1.2.3 Bitmap and Vector-Based Graphics Computer graphics can be classified into two categories: 1. Raster or Bitmap graphics 2. Vector graphics.  Bitmap graphics: i. It is pixel based graphics. 8 CU IDOL SELF LEARNING MATERIAL (SLM)

ii. The position and colour information about the image are stored in pixels arranged in grid pattern. iii. The Image size is determined on the basis of image resolution. iv. These images cannot be scaled easily. v. Bitmap images are used to represent photorealistic images which involve complex colour variations. Figure 1.4: (a) An arrow image (b) A magnified arrow image with pixel grid The above figure shows a bitmap arrow image in its actual size and magnified image with pixel grid.  Vector graphics: i. The images in vector graphics are basically mathematically based images. ii. Vector based images have smooth edges and therefore used to create curves and shapes Figure 1.5 (a) A rose image (b) A vector description of leaf of rose  iii. These images are appropriate for precise illustrations but not good for photorealistic images. iv. These images are easily scalable due to their mathematical structure. 9 CU IDOL SELF LEARNING MATERIAL (SLM)

The figure below shows a rose image and vector description of leaf of rose. Figure 1.6 (a) A bitmap image (b) A vector image 1.3 APPLICATIONS Computer graphics finds its application in various areas; some of the important areas are discussed below:  Computer-Aided Design - In engineering and architectural systems, the products are modelled using computer graphics commonly referred as CAD (Computer Aided Design). In many design applications like automobiles, aircraft, spacecraft, etc., objects are modelled in a wireframe outline that helps the designer to observe the overall shape and internal features of the objects. CAD applications are also used in computer animations. The motion of an object can be simulated using CAD.  Presentation graphics: In applications like summarizing of data of financial, statistical, mathematical, scientific and economic research reports, presentation graphics are used. It increases the understanding using visual tools like bar charts, line graphs, pie charts and other displays.  Computer Art: A variety of computer methods are available for artists for designing and specifying motions of an object. The object can be painted electronically on a graphic tablet using stylus with different brush strokes, brush widths and colours. The artists can also use combination of 3D modelling packages, texture mapping, drawing programs and CAD software to paint and visualize any object.  Entertainment: In making motion pictures, music videos and television shows, computer graphics methods are widely used. Graphics objects can be combined with live actions or can be used with image processing techniques to transform one object to another (morphing).  Education and training: Computer graphics can make us understand the functioning of a system in a better way. In physical systems, biological systems, population trends, etc., models make it easier to understand. In some training systems, graphical 10 CU IDOL SELF LEARNING MATERIAL (SLM)

models with simulations help a trainee to train in virtual reality environment. For example, practice session or training of ship captains, aircraft pilots, air traffic control personnel.  Visualization: For analysing scientific, engineering, medical and business data or behaviour where we have to deal with large amount of information, it is very tedious and ineffective process to determine trends and relationships among them. But if it is converted into visual form, it becomes easier to understand. This process is termed as visualization.  Image processing: Image processing provides us techniques to modify or interpret existing images. One can improve picture quality through image processing techniques and can also be used for machine perception of visual information in robotics. In medical applications, image processing techniques can be applied for image enhancements and is been widely used for CT (Computer X-ray Tomography) and PET (Position Emission Tomography) images.  Graphical User Interface: GUI commonly used these days to make a software package more interactive. There is multiple window system, icons, menus, which allows a computer setup to be utilized more efficiently. 1.4SUMMARY  Graphics is defined as any sketch or a drawing or a special network that pictorially represents some meaningful information. Computer graphics deals with generating images with the aid of computers.  Years of research and development were made to achieve the goals in the field of computer graphics. In 1950 the first computer driven display was used to generate only simple pictures. By the mid -1960’s large computer graphics research projects were under taken at MIT, Bell Telephone Labs and General Motors. Thus, the golden age of computer graphics began. In 1970’s the researches began to bear fruit.  Computer graphics involves display, manipulation and storage of pictures and experimental data for proper visualization using a computer. It provides methods for producing images and animations (sequence of images). It deals with the hardware as well as software support for generating images.  Basically, there are four major operations that we perform in computer graphics: i. Imaging: refers to the representation of 2D images. ii. Modelling: refers to the representation of 3D images. iii. Rendering: refers to the generation of 2D images from 3D models. iv. Animation: refers to the simulation of sequence of images over 11 CU IDOL SELF LEARNING MATERIAL (SLM)

 Computer Graphics can be broadly divided into two types - Non-Interactive Computer Graphics and Interactive Computer Graphics.  Computer Graphics can be used in digital photography, film, entertainment, electronic gadgets and all other core technologies which are required. It is a vast subject and area in the field of computer science. In most areas, computer graphics is an abbreviation of CG.  An image is basically representation of a real world object on a computer. It can be an actual picture display, a stored page in a video memory, or a source code generated by a program.  Image representation is the approximations of the real world displayed in a computer.  In computer graphics, the graphics pipeline refers to a series of interconnected stages through which data and commands related to a scene go through during rendering process. It takes us from the mathematical description of an object to its representation on the device.  Computer graphics can be classified into two categories: i. Raster or Bitmap graphics ii. Vector graphics.  Raster or Bitmap graphics is pixel based graphics. The position and colour information about the image are stored in pixels arranged in grid pattern. The Image size is determined on the basis of image resolution. These images cannot be scaled easily. Bitmap images are used to represent photorealistic images which involve complex colour variations.  In Vector graphics the images are basically mathematically based images. Vector based images have smooth edges and therefore used to create curves and shapes. These images are appropriate for precise illustrations but not good for photorealistic images. These images are easily scalable due to their mathematical structure.  Computer graphics finds its application in various areas like Computer-Aided Design, Presentation graphics, Computer Art, Entertainment, Education and training, Visualization, Image processing, Graphical User Interface etc. 1.5 KEYWORDS  CG(Computer Graphics) - Deals with generating images with the aid of computers. The term computer graphics has been used in a broad sense to describe \"almost everything on computers that is not text or sound\". 12 CU IDOL SELF LEARNING MATERIAL (SLM)

 Non-Interactive Computer Graphics - Otherwise known as passive computer graphics, the observer has no control over the image.  Interactive Computer Graphics - Involves a two-way communication between computer and user.  Image - An image is basically representation of a real world object on a computer. It can be an actual picture display, a stored page in a video memory, or a source code generated by a program.  Objects - Objects are real world entities defined in three – dimensional world coordinates. In computer graphics we deal with both 2D and 3D descriptions of an object.Image representation is the approximations of the real world displayed in a computer. A picture in computer graphics is represented as a collection of discrete picture elements termed as pixels.  Pixel - A pixel is the smallest element of picture or object that can be represented on the screen of a device like computer  Graphics pipeline - In computer graphics, the graphics pipeline refers to a series of interconnected stages through which data and commands related to a scene go through during rendering process. It takes us from the mathematical description of an object to its representation on the device.  Bitmap Graphics - Bitmap images are used to represent photorealistic images which involve complex colour variations.  Vector Graphics - The images in vector graphics are basically mathematically based images. Vector based images have smooth edges and therefore used to create curves and shapes 1.6 LEARNING ACTIVITY 1. Analyse yourday-to-day activities and make a list of places where computer graphics is used. ___________________________________________________________________________ ___________________________________________________________________________ 2. .Visit a supermarket and identify areas where interactive and non-interactive computer graphics has been used. ___________________________________________________________________________ ___________________________________________________________________________ 1.7 UNIT END QUESTIONS 13 CU IDOL SELF LEARNING MATERIAL (SLM)

A. Descriptive Questions Short Questions 1. What is computer graphics? 2. Define pixel. 3. What are the are four major operations that we perform in computer graphics? 4. Define view volume. 5. Define image and object. Long Questions 1. Explain the origin of Computer graphics. 2. Explain how computer graphics is useful in entertainment industry. 3. Which graphic system is better for photorealistic images and why? 4. Differentiate between world coordinates system and camera coordinate system. 5. How is an image is represented mathematically? B. Multiple Choice Questions 1. Where can Computer Graphics be used? a. Digital photography b. Film c. Entertainment d. All of these 2. What does GUI stand for? a. Graphical Under Interface b. Games under initiation c. Graphical User Interface d. Graphic under inspection 3. What takes usfrom the mathematical description of an object to its representation on the device? a. Objects b. Computer graphics c. Basic Graphics Pipeline d. Images 14 CU IDOL SELF LEARNING MATERIAL (SLM)

4. What can Computer graphics be classified into? a. Bitmap and Vector graphics b. Imaging and Animation c. Object and images d. None of these 5. Which images that involve complex colour variations are bitmap images used to represent? a. Clear b. Blurred c. Black and White d. Photorealistic Answers 1-d, 2-c, 3-c, 4-a, 5-d. 1.8REFERENCES References  Steven Harrington, Computer GraphicsMcGraw-Hill  J.D. Foley, A Van Dam, S. K. Feiner and R. L. Phillips, Addision Wesley Computer Graphics Principles and Practice  William M. Newman, Robert F. Sproull Principles of Interactive Computer Graphics Tata McGraw-Hill  J.D. Foley, A. Van Dam, S. K. Feiner, J.F. Hughes and R.L. Phillips, Addision Wesley Introduction to Computer Graphics Textbooks  Donald Hearn, M P. Baker Computer Graphics PHI.  David F. Rogers Procedural elements of Computer Graphics Tata McGraw Hill.  Rajesh K. Maurya Computer Graphics Wiley – India Websites  https://www.graphics.cornell.edu/about/what-computer-graphics  https://www.britannica.com/topic/computer-graphics  https://open.umn.edu/opentextbooks/textbooks/420 15 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT – 2VIDEO DISPLAY DEVICES PART I STRUCTURE 2.0 Learning Objectives 2.1 Introduction 2.2 Display Devices 2.2.1 Refresh Cathode Ray Tube 2.2.2 Raster Scan displays 2.2.3 Random Scan Displays 2.3 Architecture of Raster 2.3.1 Graphics System 2.3.2 Interaction 2.4 Random Scan Monitors 2.5 Summary 2.6 Keywords 2.7 Learning Activity 2.8 Unit End Questions 2.9 References 2.0 LEARNING OBJECTIVES After studying this unit, you will be able to:  Define video display devices.  List the different types of video display devices.  Differentiate between refresh cathode ray tube, raster scan displays and random scan displays.  Explain the architecture of raster. 2.1 INTRODUCTION The display device is an output device used to represent the information in the form of images (visual form). Display systems are mostly called a video monitor or Video display unit (VDU). 16 CU IDOL SELF LEARNING MATERIAL (SLM)

Display devices are designed to model, display, view, or display information. The purpose of display technology is to simplify information sharing. Today, the demand for high-quality displays is increasing. Some popular display devices are as follows: 1. Cathode-Ray Tube(CRT) - A cathode ray tube (CRT) is a specialized vacuum tube in which images are produced when an electron beam strikes a phosphorescent surface.It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images. Most desktop computer displays make use of CRT for image displaying purposes. 2. Colour CRT Monitor -Colour CRT Monitors are similar to CRT . The CRT Monitor display by using a combination of phosphors. The phosphors are different colours. The basic idea behind the colour CRT monitor is to combine three basic colours- Red, Green, and Blue. 3. Liquid crystal display(LCD) LCD stands for Liquid Crystal Display. It is a flat panel display technology, mainly used in TVs and computer monitors, nowadays it is used for mobile phones also. ... In LCD it has backlights that provide light to each pixel. Each pixel has a red, green, and blue (RGB) sub-pixel that can be turned on or off.- 4. Light Emitting Diode(LED) - A LED display is a flat panel display that uses an array of light-emitting diodes as pixels for a video display. Their brightness allows them to be used outdoors where they are visible in the sun for store signs and billboards. 5. Direct View Storage Tubes(DVST)A LED display is a flat panel display that uses an array of light-emitting diodes as pixels for a video display. Their brightness allows them to be used outdoors where they are visible in the sun for store signs and billboards. - 6. Plasma Display - A plasma display is a computer video display in which each pixel on the screen is illuminated by a tiny bit of plasma or charged gas, somewhat like a tiny neon light. Plasma displays are thinner than cathode ray tube ( CRT ) displays and brighter than liquid crystal displays ( LCD ). 7. 3D Display - 3D displays, on the other hand, are designed to simulate depth using stereoscopic vision, presenting two different images so that the viewers' eyes interpret the images as a single 3D image. The displays are two dimensional, but the brain perceives three-dimensional depth. The most common type of 3D display is based on shutter technology, which uses special LCD glasses to synchronize two images. This technology has been used with computers for many years through specialized hardware. Now, it's possible to produce 3D images in higher resolutions with greater refresh rates. 17 CU IDOL SELF LEARNING MATERIAL (SLM)

2.2 DISPLAY DEVICES There are various types of displays like CRT, LCD and Plasma. We will discuss each of these three in brief 2.2.1 Refresh Cathode Ray Tube Figure. 2.1 below illustrates the basic operation of a CRT. A beam of electrons (cathode rays), emitted by an electron gun, passes through focusing and deflection systems that direct the beam towards specified position on the phosphor-coated screen. The phosphor then emits a small spot of light at each position contacted by the electron beam. Because the light emitted by the phosphor fades very rapidly, some method is needed for maintaining the screen picture. One way to keep the phosphor glowing is to redraw the picture repeatedly by quickly directing the electron beam back over the same points. This type of display is called a refresh CRT Figure 2.1 Elements of a CRT screen The primary components of an electron gun in a CRT are the heated metal cathode and a control grid (Figure. 2.1). Heat is supplied to the cathode by directing a current through a coil of wire, called the filament, inside the cylindrical cathode structure. This causes electrons to be “boiled off” the hot cathode surface. In the vacuum inside the CRT envelope, negatively charged electrons are then accelerated toward the phosphor coating by a high positive voltage. The accelerating voltage can be generated with a positively charged metal coating on the inside of the CRT envelope near the phosphor screen, or an accelerating anode can be used, a in fig below . Sometimes the electron gun is built to contain the accelerating anode and focusing system within the same unit. Spots of light are produced on the screen by the transfer of the CRT beam energy to the phosphor. When the electrons in the beam collide with the phosphor coating, they are stopped and there are stopped and their kinetic energy is absorbed by the phosphor. Part ofthe beam energy s converted by friction into heat energy, and the remainder causes electron in the phosphor atoms to move up to higher quantum- energy levels. After a short time, the “excited” phosphor electrons begin dropping back to their stable ground state, giving up their extra energy as small quantum of light energy. What we see on the screen is the combined effect of all the electrons light emissions: a glowing 18 CU IDOL SELF LEARNING MATERIAL (SLM)

spot that quickly fades after all the excited phosphor electrons have returned to their ground energy level. The frequency (or colour ) of the light emitted by the phosphor is proportional to the energy difference between the excited quantum state and the ground state. Different kinds of phosphor are available for use in a CRT. Besides colour, a major difference between phosphors is their persistence: how long they continue to emit light (that is, have excited electrons returning to the ground state) after the CRT beam is removed. Persistence is defined as the time it takes the emitted light from the screen to decay to one-tenth of its original intensity. Lower-persistence phosphors require higher refresh rates to maintain a picture on the screen without flicker. A phosphor with low persistence is useful for animation; a high- persistence phosphor is useful for displaying highly complex, static pictures. Although some phosphor have a persistence greater than 1 second, graphics monitor are usually constructed with a persistence in the range from 10 to 60 microseconds 2.2.2 Raster Scan displays A Raster Scan Display is based on intensity control of pixels in the form of a rectangular box called Raster on the screen. Information of on and off pixels is stored in refresh buffer or Frame buffer. Televisions in our house are based on Raster Scan Method. The raster scan system can store information of each pixel position, so it is suitable for realistic display of objects. Raster Scan provides a refresh rate of 60 to 80 frames per second. Frame Buffer is also known as Raster or bit map. In Frame Buffer the positions are called picture elements or pixels. Beam refreshing is of two types. First is horizontal retracing and second is vertical retracing. When the beam starts from the top left corner and reaches the bottom right scale, it will again return to the top left side called at vertical retrace. Then it will again more horizontally from top to bottom call as horizontal retracing shown in fig: 19 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.2: Raster scan display Raster scan displays: A rectangular array of points or dots. In a raster scan system, the electron beam is swept across the screen, one row at a time from top to bottom. As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots. See the above figure. Horizontal retrace: The return to the left of the screen, after refreshing each scan line.  Vertical retrace: At the end of each frame (displayed in 1/80th to 1/60th of a second) the electron beam returns to the top left corner of the screen to begin the next frame. Figure 2.3:Horizontal and vertical retrace Types of Scanning or travelling of beam in Raster Scan 1. Interlaced Scanning 2. Non-Interlaced Scanning In Interlaced scanning, each horizontal line of the screen is traced from top to bottom. Due to which fading of display of object may occur. This problem can be solved by Non-Interlaced scanning. In this first of all odd numbered lines are traced or visited by an electron beam, then in the next circle, even number of lines are located. For non-interlaced display refresh rate of 30 frames per second used. But it gives flickers. For interlaced display refresh rate of 60 frames per second is used. Advantages: 1. Realistic image 2. Million Different colors to be generated 3. Shadow Scenes are possible. 20 CU IDOL SELF LEARNING MATERIAL (SLM)

Disadvantages: 1. Low Resolution 2. Electron beam coordinated to whole screen not exclusively to those parts of the screen where picture is to be drawn so tedious when the drawn picture estimate is especially not as much as the whole screen 3. Expensive Differentiate between Random and Raster Scan Display: Table 2.1: Random scan vs Raster scan Raster Scanning  In cameras and displays, some time is required to advance the scanning operation to retrace from one line to the next and from one picture to the next. These intervals are called blanking intervals.  In conventional CRT display the electron beam must be extinguished (blanked) during these time intervals. The horizontal blanking time lies between scan lines, and vertical blanking lies between frames (or fields).  The raster structure of 525/59.94 and 625/50 digital video systems, including these blanking intervals. In analog video, sync information is conveyed during the blanking intervals. 21 CU IDOL SELF LEARNING MATERIAL (SLM)

 The horizontal and vertical blanking intervals required for a CRT display are quite large fractions of the line time and frame time: in 525/59.94, 625/50, and 1920 × 1035 systems, vertical blanking occupies 8 percent of each frame period.  Although in principle a digital video interface could omit the blanking intervals and use a clock having a lower frequency than the sampling clock, this would be impractical.  Digital video standards use interface clock frequencies chosen to match the large blanking intervals of typical display equipment.  A digital video interface may convey audio signals during blanking; a digital video tape recorder might record error correction information in these intervals. Figure 2.4: Raster scanning 2.2.3 Random Scan Displays Random Scan System uses an electron beam which operates like a pencil to create a line image on the CRT screen. The picture is constructed out of a sequence of straight-line segments. Each line segment is drawn on the screen by directing the beam to move from one point on the screen to the next, where its x & y coordinates define each point. After drawing the picture. The system cycles back to the first line and design all the lines of the image 30 to 60 time each second. The process is shown in figure 2.5 22 CU IDOL SELF LEARNING MATERIAL (SLM)

Random scan display is the use of geometrical primitives such as points, lines, curves, and polygons, which are all based upon mathematical equation. In a random scan display, a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Random scan monitors draw a picture one line at a time. See the figure 2.6below Figure 2.5: Random Scan display Random-scan monitors are also known as vector displays or stroke-writing displays or calligraphic displays. Advantages: 1. A CRT has the electron beam directed only to the parts of the screen where an image is to be drawn. 2. Produce smooth line drawings. 3. High Resolution Disadvantages: 1. Random-Scan monitors cannot display realistic shades scenes. 23 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.6 Random scan display Refresh rate depends on the number of lines to be displayed.  Picture definition is now stored as a line-drawing commands an area of memory referred to as refresh display file.  To display a picture, the system cycle through the set of commands in the display file, drawing each component line in turn.  Random scan displays are designed to draw all the component lines of a picture 30 to 60 times each second.  Random scan displays have higher resolution than raster systems. 2.3 ARCHITECTURE OF RASTER Raster Scan Display basically employs a Cathode Ray Tube (CRT) or an LCD panel for display. The CRT works just like the picture tube of a television set. Raster Scan Display viewing surface is coated with a layer of arrayed phosphor dots. At the back of the CRT is a set of electron guns (cathodes) that produce a controlled stream of electrons that is called electron beam. The phosphor material emits light when struck by these high-energy electrons. 2.3.1 Graphics System The frequency and intensity of the light emitted depends on the type of phosphor material used and the energy of the electrons. To produce a picture on the screen, these directed electron beams start at the top of the screen and scan rapidly from left to right along the row of phosphor dots. They return to the leftmost position one line down and scan again, and 24 CU IDOL SELF LEARNING MATERIAL (SLM)

repeat this to cover the entire screen. The return of the beam direction to the leftmost position one line down that is called Horizontal Retrace. Figure 2.7: Organization of a raster system Interactive raster-graphics systems typically employ several processing units. In addition to the CPU, a special purpose processor called the video controller or display controller is used to control the operation of the display device. The figure shows the organization of a raster system. The frame buffer can be anywhere in the system memory, and the video controller access the frame buffer to refresh the screen. Video Controller A fixed area of the system memory is reserved for the frame buffer, and the video controller is given direct access to the frame buffer memory. The co-ordinates of the graphics monitor starts at the lower left screen corner. Positive x values increasing to the right and y values increasing from bottom to top. Figure 2.8: Refresh operation of video controller 25 CU IDOL SELF LEARNING MATERIAL (SLM)

Two registers are used to store the co-ordinates of the screen pixels. Initially x=0 and y=ymax. The value stored in the frame buffer corresponding to this pixel position is retrieved. And the x value is incremented by 1 and the corresponding y value is retrieved, like that the pixel values are retrieved line by line. Once the last pixel is reached again the registers are reset to initial value to repeat the process. Display Processor The purpose of the display processor or graphics controller is to free the CPU from the graphics chores. In addition to the system memory a separate display processor memory area can also provide. A major task of the display processor is digitizing a picture definition given in an application program into a set of pixel-intensity values for storage in the frame buffer. This digitization process is called scan conversion. Lines and other geometric objects are converted into set of discrete intensity points. Characters can be defined with rectangular grids, or they can be defined with curved outlines. To reduce the memory space required to store the image information, each scan line are stored as a set of integer pairs. One number of each pair indicates an intensity value, and the second number specifies number of adjacent pixels the scan line that is also having same intensity. This technique is called run-length encoding. 2.3.2 Interaction A number of different feedback levels in the image synthesis pipeline can be identified if one takes a new look at the basics of high quality three-dimensional (3-D) raster graphics for CAD. A user interacts with the visible parts of a 3-D model at each of the levels. We provide direct access to graphics objects to support pointing and identification. These are the fundamental actions that underlie every change a user makes. Changing pictures form the key to the architecture. Actual pixels are not needed for interaction. If we take this observation seriously and ruthlessly pare away other elements we get a radical prescription for a graphics architecture. One where the visible surfaces of objects are explicitly identified and without any mandate for a frame buffer. We believe that our research shows that such a machine, which harkens back to the calligraphic roots of graphics displays, can be built. Here on an ongoing project to build such a system. In the past four years the design has been completed, the critical components have been made 26 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.9: Graphical data that are relevant for interaction. and functions simulated in detail. This paper is a description of the complete design and early experiences. The rest of this section presents an outline of the architecture. The major new components follow from the bottom up: first, the display controller comprising the pixel generator (or x-processor) and the shading processor (or Y-processor), and then hidden surface removal. In The system is evaluated in the light of our experience so far and with reference to its antecedents and current alternatives. The functional elements of the display architecture are shown. In our architecture the frame buffer is replaced by a structured list of objects which can be 'pointed' at refresh rate. To this end a powerful VLSI-based hardware block containing a systolic array of processors produces a full colour pixel stream at video refresh rate. This block is fed directly from the structured object list. As a result a selected object can be highlighted or moved instantaneously. The processors are also capable of producing Phong shaded 3-D objects or 2-D textures at this rate. The size of the structured list dependent on the image complexity. For reasonable complex images the size is about the same as a conventional frame buffer, with the advantage that the object list is resolution independent (it does not become larger for higher resolutions). The structured list is also a much more organized data structure and can support more sophisticated operations than a frame buffer. At higher levels of the architecture the objects become more complex (but also fewer - less fragmented) with information about light sources, textures and viewing. Here representations for incremental changes typical of real-time interaction are favoured These requirements appear to be satisfiable in the short term by powerful but off-the-shelf parallel hardware. At the lowest level custom components are needed: these have already been built. 27 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.10: Functional elements of display architecture. the y and x processors are part of the display controller Display Controller The graphics requirements are essentially real-time support of the Phigs+ standard, with Phong shading as the best quality shading method. This degree of realism must be achieved at 50-60 frames per second in an interactive setting where the user is free to alter models, position of the lights and viewpoint. The current state-of-the-art is real-time Gouraud shading. The next hurdle in real-time realism is therefore the familiar Phong illumination equation. The refresh process of a graphics display device is performed by a display controller. In calligraphic systems this module interpreted line drawing instructions collected in a display list and used this to steer the electron beam (both location and intensity). In current raster graphics systems the function of a display controller is reduced to reading of pixel intensity information stored in successive memory locations of a frame buffer and transforming that information into the video signals. In our system architecture the display controller interprets 'area drawing instructions' in the structured object list which describe non overlapping areas on the screen and their colouring information and transforms that into the video signals. The row by row nature of the video signal suggests splitting this scan- conversion process in the horizontal (x) and vertical (Y) direction, This led to a display controller architecture with different types of processing elements (x-processors and Y- processors), and different levels of complexity for the algorithms running on them Uayasinghe91 a]. For each scan line, the intersection of objects with the scan line as well as the colour function along that scanline is calculated by an array of Yprocessors (Le., shading processors), These produce scanline commands which are send to a one-dimensional systolic array of x-processors (Le., the pixel generator). These process and sort the commands and produce a stream of pixel values. 28 CU IDOL SELF LEARNING MATERIAL (SLM)

Pixel Generator The pixels are generated by one one-dimensional systolic array of X-processors per colour. There is no space to introduce the full instruction repertoire of the x-processors here (see appendix A). The repertoire supports smooth shading, i.e. a continuous intensity and continuous derivative of the intensity. Thus, the x-processors generate quadratic interpolated intensities by forward differencing. Higher order interpolation (in fact any higher order) for the purpose of anti-aliasing and advanced illumination models is supported as well. The processors use 12 bit pixel addressing and operate on 36 bit fixed point intensity values. This precision is sufficient for second order forward differencing along the designed maximum span of 4K pixels. For higher order forward differencing, the size of the spans should be limited to assure sufficient accuracy. Commands for a scanline issued by the v- processors enter the x-processor array on one side and travel through the array/currently at a rate of 12 ns per processor. Commands operate on a span of pixels, and results of several commands on a pixel accumulate. Shading Processor The information to drive shading- or V-processors is contained in the structured object list V- processors produce the instructions for the pixel generator. The V-processors operate at the frame refresh rate and go through a complete cycle once every video frame. Their input data are produced at the interaction or animation rate (between 12 and 24 cycles per second). The output goes to the pixel processors operating at the line refresh rate. The task of these processors can also be described as having to change 2-D display information into 1-0 scanline information. The third dimension has been dealt with earlier by projection and hidden surface removal. The geometry can be specified solely in terms of (2- D) display coordinates but (3-~) world coordinates are still needed for the shading calculations. The edges of the surface primitives (triangles or trapezoids) are simple enough to find. Shading (especially Phong shading) and anti-aliasing are more of a challenge and we give an outline of our methods to achieve the high speed necessary. The major cost in Phong shading is the renormalization (via a square root and a division) and exponentiation that has to occur after each interpolation step. Look-up tables can be used for square roots and exponentiation but this costs storage and is not feasible in highly parallel systems such as ours. Another approach to this problem is to recast the Phong shading model, but without lapsing into expensive Gouraud shaders or being unable to deal with all practical situations. Phong shading itself is nothing more (or less) than a very good practical approximation: it is not an end in itself. In [Kuijk89] we introduced a method for quadratic Phong shading via angular interpolation. It has the lowest per pixel cost in time and storage of any method we are aware of. 29 CU IDOL SELF LEARNING MATERIAL (SLM)

We interpolate vectors by rotation rather than by the standard linear interpolation and renormalization. The difference is unimportant provided we remain consistent - both approaches are equally 'wrong' since both ignore perspective projection effects. If either the light source or the viewer are not at infinite distance then we apply an approximation. In the case of diffuse illumination this can be understood intuitively as replacing a surface with a light source near it with a more convex surface with the light source at infinity. A similar approximation exists for specular reflection. Anti-aliasing in the form of exact area integration is applied. Object space hidden surface removal preserves the necessary information on pixel coverage. Where pixel coverage gradually increases along a scanline this is treated as a linear modulation of the quadratic shading function. This results in a cubic expression which is passed on to the pixel generator. Hidden Surface Removal In our architecture, the hidden surface removal (HSR) takes place in object space. This 21f2-D space is the result of a perspective transformation on the 3-D scene so that a simple projection along the Z-axes produces the 2-D image. Hidden surface removal comes down to sorting. Therefore we make use of a pre-sorted representation of the objects and store them in a data structure on a location which reflects the x- and y-position of the object. The pre-sorted representation of the objects does not only reduce the overlap calculations needed for the HSR, but also simplifies the scan conversion process. The data structure in which objects are stored is designed to reduce the search space and to be able to (evenly) distribute the data for a multi-processor implementation. This makes the HSR and other operations which involve identification based on location more efficient. The interactive applications envisioned require incremental picture changes. Known object space HSR algorithmsoperate on a complete scene description and produce the complete set of visible objects. Therefore we defined a set of logical operations on the 2'/.2-D objects so that individual objects can be added and deleted. These operations amongst others involve subtraction, overlap calculation and union of objects. All objects have attributes that influence the shading calculations. The objects that the logical operations produce inherit a logical combination of the attributes of the original objects. This feature allows the system to efficiently make objects invisible or transparent 2.4 RANDOM SCAN MONITORS Random-scan Systems An application program is input and stored in the system memory along with a graphics package. Graphics commands in the program are translated by the graphics package into a display file stored in the system memory. This display file is then accessed by the display processor to refresh the screen. The display processor cycles through each command in the display file program once during every refresh cycle. Sometimes the display processor in a random-scan system is refreshed to as a display processing unit or a graphics controller. 30 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 2.11: Random-scan system Graphic patterns are drawn on a random scan system by directing the electron beam along the component lines of the picture. Lines are defined by the values for their co-ordinate endpoints, and these input co-ordinate values are converted to x and y deflection voltages. A scene is then drawn one line at a time by positioning the beam to fill in the line between specified endpoints. When operated as a random scan unit a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Random scan monitors draws a picture one line at a time and for this reason also called vector display or stoke writing display or calligraphic displays. The component lines of a picture can be drawn and refreshed by a random scan system, in any specified order. A pen plotter operates in a similar way which is an example of random scan hard copy device. Refresh rate on a random scan system depends upon the number of lines to be displayed. Picture definition is now stored as a set of line drawing commands in an area of memory referred to as the refresh display file or simply the refresh buffer. To display a specified picture the system cycle’s through the set of commands in the display file drawing cache component line in turn. After all, line drawing commands have been processed, the system cycle back to the first line command in the list. Random scan displays are design to draw all the component line of the picture 30-60 times per second. High-quality vector systems are capable of handling approximately one lakh short lines at this refresh rate. These systems are designed for line drawing applications and cannot display realistic shaded scenes. Since, picture definition is stored as set of line drawing instructions and not as a set of intensity value for all screen points. Random display generally have higher reduction than raster system. 2.5 SUMMARY  A beam of electrons (cathode rays), emitted by an electron gun, passes through focusing and deflection systems that direct the beam towards specified position on the phosphor-coated screen. The phosphor then emits a small spot of light at each position 31 CU IDOL SELF LEARNING MATERIAL (SLM)

contacted by the electron beam. Because the light emitted by the phosphor fades very rapidly, some method is needed for maintaining the screen picture.  In the vacuum inside the CRT envelope, negatively charged electrons are then accelerated toward the phosphor coating by a high positive voltage. The accelerating voltage can be generated with a positively charged metal coating on the inside of the CRT envelope near the phosphor screen, or an accelerating anode can be used.  A rectangular array of points or dots. In a raster scan system, the electron beam is swept across the screen, one row at a time from top to bottom. As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots.In a random scan display, a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Random scan monitors draw a picture one line at a time.  An application program is input and stored in the system memory along with a graphics package. Graphics commands in the program are translated by the graphics package into a display file stored in the system memory.  This display file is then accessed by the display processor to refresh the screen. The display processor cycles through each command in the display file program once during every refresh cycle.  When operated as a random scan unit a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Random scan monitors draws a picture one line at a time and for this reason also called vector display or stoke writing display or calligraphic displays. The component lines of a picture can be drawn and refreshed by a random scan system, in any specified order.  These systems are designed for line drawing applications and cannot display realistic shaded scenes. Since, picture definition is stored as set of line drawing instructions and not as a set of intensity value for all screen points.  The overall aim of our research is to develop a new architecture for an interactive workstation. A novel feature of this architecture is that there is no frame buffer - this was done mainly to improve interactive performance, but one could also argue that if 24 frames per second are needed then one might as well do 60 frames per second and get rid of the frame buffer which becomes a bottle-neck at high update rates. This feature has a number of implications, for example, that the smallest pick primitive becomes a visible surface and not a pixel, and that object space hidden surface removal is required.  It also means that fully shaded pixels that depend on multiple light sources have to be produced every 12 ns or so, depending on resolution. The object space approach makes it possible to perform incremental updates. This reduces the number of 32 CU IDOL SELF LEARNING MATERIAL (SLM)

computations involved on the levels above the rasterization level and thus improves the interactive behaviour of the system.  The two-level implementation of the display controller (x- and Y-processors) makes it possible to scale the system in two ways. The number of Y-processors can be selected to meet the requirements on the maximum image complexity (Le. number of objects). The number of x-processors can be adjusted to accommodate all resolutions (up to 4K pixels per scanline). The current maximum throughput rate of the x-processors is sufficient to support high resolution systems. It can handle the refresh of 2.46 M Phong shaded polygons of 5 x 5 pixels per second (60 x41 K). Since this first version was a low cost design, it is expected that a redesign and a better technology will improve this even further. Besides, the throughput rate can be multiplied by using multiple arrays.  In Random-Scan Display electron beam is directed only to the ares of screen where a picture has to be drawn. It is also called vector displays, as it draws picture one line at time. It can draw and refresh component lines of a picture in any specified sequence. Pen plotter is an example of random-scan displays.  The raster scan monitors make use of the whole screen for displaying the object while in random screen monitors the certain part of the screen is used where the electron beam is projected. Raster scan uses screen points/pixels to draw an image whereas a random scan employs mathematical functions for painting the image.  In random scan, mathematical function is used for image or picture rendering. While in which, for image or picture rendering, raster scan uses pixels.  Random scan monitors are used to draw a picture in one line at a time and are thus also referred to as vector displays. The cathode ray tube when operates as a random scan display device directs the beam of an electron only to those areas of the screen where display or a picture has to be drawn.  Random-scan system mainly designed for Line-drawing applications. The video monitor is the commonly used output device. Bit map frame buffer is always 1 bit per pixel. 2.6 KEYWORDS  Horizontal Retrace - The return of electron beam to the left of the screen after refreshing each scan line.At the end of each scan line, the electron beam returns to the left side of the screen to begin displaying the next scan line. The return to the left of the screen, after refreshing each scan line is called the horizontal retrace.  Vertical Retrace - The return of electron beam to the left top corner of the screen after the completion of each frame.Alternatively referred to as a vertical blanking 33 CU IDOL SELF LEARNING MATERIAL (SLM)

interval or the vertical sync signal, vertical retrace is a measurement of time related to video displays. It represents the amount of time between the end of one frame being drawn, and the beginning of the next frame.  CRT - A cathode-ray tube is a vacuum tube containing one or more electron guns, the beams of which are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms, pictures, radar targets, or other phenomena. A CRT on a television set is commonly called a picture tube.  VDU - An electronic visual display, informally a screen, is a display device for presentation of images, text, or video transmitted electronically, without producing a permanent record. Electronic visual displays include television sets, computer monitors, and digital signage.  LCD - A liquid-crystal display is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly, instead using a backlight or reflector to produce images in colour or monochrome. 2.7 LEARNING ACTIVITY 1. Create a survey about the feelings created byCRT in your olden days. ___________________________________________________________________________ __________________________________________________________________________ 2. Create a session about the raster scan display used in your locality. ___________________________________________________________________________ ___________________________________________________________________________ 2.8 UNIT END QUESTIONS A. Descriptive Questions Short Questions 1. What is CRT? 2. Define LCD. 3. Describe LED? 4. Define DVST. 5. Explain VDU. Long Questions 34 CU IDOL SELF LEARNING MATERIAL (SLM)

1. Explain refresh cathode ray tube. 2. Explain raster scan displays. 3. Describe about random scan displays 4. Explain graphic systems. 5. Explain random scan monitors. B. Multiple Choice Questions 1. What are Random scan and Raster scan techniques? a. Techniques to display an image on the screen b. Line Drawing Techniques c. Polygon Drawing Techniques d. None of these 2. Which is best suited for a smooth line drawing on the screen? a. Random Scan Display Algorithm b. Raster Scan Display Algorithm c. Both a. and b. d. None of these 3. Which is best suited for a realistic shaded image drawing on the screen? a. Random scan display algorithm b. Raster scan display algorithm c. Both Random scan and raster scan display. d. None of these 4. Which is correct in accordance with the Random Scan Display Algorithm? a. It is best suited for line drawing algorithm. b. It has a high resolution. c. It has an electron beam which strikes only that part of the screen where the drawing is needed. d. All of these 5. Which are the types of scanning or travelling of beam in a raster scan display 35 technique? a. Interlaced Scanning CU IDOL SELF LEARNING MATERIAL (SLM)

b. Non- Interlaced Scanning c. Spiral Scanning d. All of these Answers 1-a, 2-a, 3-b, 4-d, 5-c 2.9 REFERENCES References  Murtha, T., S. A. Lenway, and J. A. Hart. (2001). Managing New Industry Creation. Stanford, CA: Stanford University Press.  Young, R. (2005). Survival of the Fittest: Managing the Peaks and Valleys of Supply/Demand. Presented at the 7th Annual DisplaySearch U.S. FPD Conference, Austin, Texas  Wood, C. (1992). The Bubble Economy: Japan's Extraordinary Speculative Boom of the '80s and the Dramatic Bust of the '90s. New York: Atlantie Monttrly Press. Textbooks  Castellano, J. A. (2005). Litluid GoLd: The Story of Liquid Crystal Displays and the Creation of an Industry. Hackensack, N.J.: World Scientific.  Hutchison, M. M. (1998). The Political Economy of Jaltanese Monetary Poiic_ri Cambridge: MIT Press.  Johnstone, B. (i999). We Were Buning: Jaltanese Entrepreneurs and the Forging oJ the Electonic Age. Boulder, CO: Basic Books. Websites  http://news.softpedia.com/news/The-transition-to-TFl-LCD-could-cut-downprices-on- cell-phones- 1 645. shtml.  http://sharpworld.c om/corp orute I ec o I rcpoft / 2005pdfi sharp09e. pd f .  https://www.thiyagaraaj.com/tutorials/computer-graphics/overview-of-graphics- system/3-architecture-and-components-of-raster-scan-systems-random-scan-systems 36 CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT – 3VIDEO DISPLAY DEVICES PART II STRUCTURE 3.0 Learning Objectives 3.1 Introduction 3.2 Colour CRT-Monitors 3.3 Colour Generating Techniques 3.4 Direct View Storage Tube 3.5 Flat Panel Display 3.6 Graphics Monitors 3.7 Workstations 3.8 Summary 3.9 Keywords 3.10 Learning Activity 3.11 Unit End Questions 3.12 References 3.0 LEARNING OBJECTIVES After studying this unit, you will be able to:  Explain the various types of flat panel displays.  Illustrate the concept of colour CRT monitors.  Explain the colour generating techniques.  Describe about graphic monitors. 3.1 INTRODUCTION Video display device means an electronic device with a viewable screen of 4 inches or larger that contains a tuner that locks on to a selected carrier frequency and is capable of receiving and displaying television or video programming via broadcast, cable, or satellite. Video display device includes, but is not limited to, a direct view or projection television whose display technology is based on cathode ray tube (CRT), plasma, liquid crystal (LCD), digital light processing (DLP), liquid crystal on silicon (LCOS), silicon crystal reflective display (SXRD), light emitting diode (LED), or similar technology. 37 CU IDOL SELF LEARNING MATERIAL (SLM)

Video display device means an electronic device with an output surface that displays or is capable of displaying moving graphical images or visual representations of images sequences or pictures that show a number of quickly changing images on a screen to create the illusion of motion. Video display device includes a device that is an integral part of the display and cannot easily be removed from the display by the consumer and that produces the moving images on the screen. A “video display device” may use a cathode-ray tube (CRT), liquid crystal display (LCD), gas plasma, digital light processing, other image projection technology or imaging display technologies. Video display device means an electronic device with an output surface that displays, or is capable of displaying, moving graphical images or a visual representation of image sequences or pictures, showing a number of quickly changing images on a screen in fast succession to create the illusion of motion, including, if applicable, a device that is an integral part of the display, in that it cannot be easily removed from the display by the consumer, that produces the moving image on the screen. A video display device may use, but is not limited to, a cathode ray tube (CRT), liquid crystal display (LCD), gas plasma, digital light processing, or other image projection technology. Video display device means a device that has an output surface having a viewable area greater than four inches when measured diagonally that displays moving graphical images or a visual representation of image sequences or pictures. It shows a number of quickly changing images on a screen in fast succession to create the illusion of motion, including but not limited to a device that is an integral part of the display that cannot be easily removed from the display by the consumer and that produces the moving image on the screen and includes technology using a cathode ray tube, liquid crystal display, gas plasma, digital light processing, or other type of image projection technology. 3.2 COLOR CRT-MONITORS A CRT monitor displays colour pictures by using a combination of phosphors that emit different-coloured light. The two basic techniques for producing colour displays with a CRT are  Beam-penetration method  The shadow-mask method. Beam Penetration Method The Beam-Penetration method has been used with random-scan monitors. In this method, the CRT screen is coated with two layers of phosphor, red and green and the displayed color depends on how far the electron beam penetrates the phosphor layers. This method produces 38 CU IDOL SELF LEARNING MATERIAL (SLM)

four colors only, red, green, orange and yellow. A beam of slow electrons excites the outer red layer only; hence screen shows red color only. A beam of high-speed electrons excites the inner green layer. Thus screen shows a green color. Figure 3.1: Beam penetration method Advantages: 1. Inexpensive Disadvantages: 1. Only four colors are possible 2. Quality of pictures is not as good as with another method. Used with random scan monitors 1. Two Layers of Phosphor is used Red and Green 2. The displayed colour depends on how far the electron beam penetrates into the phosphoric layers 3. Only 4 colours are possible Red, Green, Orange, Yellow 4. Intensity is based on the Speed of the beam Shadow Masking Method  Shadow Mask Method is commonly used in Raster-Scan System because they produce a much wider range of colors than the beam-penetration method.  It is used in the majority of color TV sets and monitors. Construction A shadow mask CRT has 3 phosphor color dots at each pixel position.  One phosphor dot emits Red light  Another emits Green light 39 CU IDOL SELF LEARNING MATERIAL (SLM)

 Third emits Blue light This type of CRT has 3 electron guns, one for each color dot and a shadow mask grid just behind the phosphor coated screen. Shadow mask grid is pierced with small round holes in a triangular pattern. Figure 3.2 shows the delta-delta shadow mask method commonly used in color CRT system. Figure 3.2: Shadow masking method Figure 3.3: Shadow mask CRT 40 Working Triad arrangementsare red, green, and blue guns. CU IDOL SELF LEARNING MATERIAL (SLM)

The deflection system of the CRT operates on all 3 electron beams simultaneously; the 3 electron beams are deflected and focused as a group onto the shadow mask, which contains a sequence of holes aligned with the phosphor- dot patterns. When the three beams pass through a hole in the shadow mask, they activate a dotted triangle, which occurs as a small color spot on the screen. The phosphor dots in the triangles are organized so that each electron beam can activate only its corresponding color dot when it passes through the shadow mask. Inline Arrangement Another configuration for the 3 electron guns is an Inline arrangement in which the 3 electron guns and the corresponding red-green-blue color dots on the screen, are aligned along one scan line rather of in a triangular pattern. This inline arrangement of electron guns in easier to keep in alignment and is commonly used in high-resolution color CRT's. Figure 3.4: Triad and in-line arrangements of red, green and blue electron guns of CRT for colour monitors Advantages 1. Realistic image 2. Million different colors to be generated 3. Shadow scenes are possible Disadvantages 1. Relatively expensive compared with the monochrome CRT. 2. Relatively poor resolution 3. Convergence Problem The features of shadow mask method are listed below. 41 CU IDOL SELF LEARNING MATERIAL (SLM)

1. Used in Raster Scan Systems 2. Produces wider range of colours than beam penetration method 3. Each pixel position has three phosphor dots 4. This type of CRT possess 3 electron guns one for each dot 5. Shadow mask grid placed just behind the screen. 6. Colour Variations i. Varying the intensity levels of the three electron beams 7. 24 bits of storage per pixel 8. Arrangements – i. Delta-Delta Method ii. In-Line Method Delta-Delta Method Figure 3.5: Delta-Delta method  Commonly used in colour CRTs.  Mask holds the series of holes aligned with phosphor dot patterns (triangular pattern).  Beam pass through the hole in the mask & activate the dot triangle which appears as a colour spot. In-Line Method 42 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.6: In-Line method  Three Electron guns, the tri-colour dots in the screen are aligned along one scan line instead of triangular shape  Commonly used in high resolution colour CRTs 3.3 COLOR GENERATING TECHNIQUES Colour vision is a very complicated biological and psychological phenomenon. It can be described inmany different ways, including by physics, by subjective observation, or by the tri-stimulus representationcommonly used in computers The Physical Description of Colour As we noted previously, light has a wavelength (), which can be measured accurately, and anenergy or intensity. Lasers produce light of one particular wavelength, but generally visible light is adistribution of energy into a band of wavelengths. Figure3.1 shows a distribution of light which we would perceive as red in colour along with the distribution of energy found in sunlight, which we perceive as light yellow. The wavelength range of the visible spectrum is approximately from 400 to 700 nano-meters. 43 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.7: Colour as an energy distribution In the eye we have just three distinct 'cone' cells for detecting light energy. These respond to a band of wavelength centred around red (600), green (560) and blue (440); respectively. The bands overlap, so, for example green light excites all three types. The consequence of this is that each type of cell may be excited similarly from very different energy distributions. Any distribution of wavelengths will be perceived by us as a single colour, but two entirely different distributions of intensities could be perceived as the same colour. Subjective Observation of Colour Two colours are said to be equivalent when an observer says that they are equivalent. Selecting three pure light sources (R, G, B) and mixing them together while varying their respective intensities, one may be able to create a large number of colours. Each colour satisfies the following linear combination: X = r*R + g*G + b*B where r, g, b are intensities of the red, green and blue light sources. Not all colours can be matched in this way. However, by adding one of the pure colours to an unknown, unmatchable colour, we can make a match. This is in effect subtracting a colour from the mix X + r*R = g*G + b*B or X + g*G = r*R + b*B 44 CU IDOL SELF LEARNING MATERIAL (SLM)

or X + b*B = r*R + g*G The representation of colours as a mixture of three components is called the tri-stimulus representation, and is very commonly used in monitors and other active colour devices. The pure colours used are red green and blue, and are referred to as the additive primary colours The Standard Additive Linear System (CIE) A linear system is a mathematical model of a system based on the use of a linear operator. Linear systems typically exhibit features and properties that are much simpler than the nonlinearcase. As a mathematical abstraction or idealization, linear systems find important applications in automatic control theory, signal processing, and telecommunications. For example, the propagation medium for wireless communication systems can often be modeled by linear systems. Matching allows us to determine an rgb representation of any colour, even though the scales include negative numbers. The scales use depend on the wavelengths of the sources for matching and are not standard. In order to create a manageable standard system, a committee of scientists devised the CIE Chromaticity Diagram, in which colours are specified by a linear combination of three light sources normalised to the positive range [0..1] to avoid any negative values. The three principal colours would normally require a three dimensional diagram, but by using further normalisation a two dimensional diagram is produced. Suppose a colour is defined by COLOUR = r + g + b where r, g, and b. If we divide both sides of this equation with (r+g+b) and get: x = r/(r+g+b) the normalised red component, y = g/(r+g+b) the normalised green component z = b/(r+g+b) the normalised blue component and x + y + z = 1 So, knowing two of the three normalised colour components (x,y) the third one can be determined, i.e. z=1-x-y. All normalised colour values can now be shown on a two-dimensional figure of diagram 3.2. 45 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.8: CIE diagram The horseshoe shaped curve represents the visible pure colours with their approximate physical wavelength running from 380 to 780 nm. We can see that just below 500 nm the red component is zero and the blue and green are approximately equal which would correspond to the colour cyan. The straight part of the diagonal line on the right represents the condition that x+y=1 which means that the blue component is zero. The straight line at the bottom is a combination of red and blue, which has no equivalent single wavelength colour. It is called the magenta line. The usefulness of this diagram is that it is based on a linear additive system and the addition of colour components can be done graphically. Graphical Manipulation of Colour Parameters The figurebelow shows a CIE diagram. The whitepoint (x=y=z=1/3) has equal strength of all three basiccomponents. Pure colours, around the edge of thehorseshoe, are called pure or fully saturated colours. 46 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.9: Colour Computations Ifwe take a pure colour, say 595 nm on the diagram, theline connecting this point and the white point containsall the possible colours which can be achieved byadding white to this pure colour. If we extend this lineand on the other side it hits the curve at another purecolour point (485 nm in this case), which is called thecomplement because mixing the two makes white.Saturation, or the degree of purity, of a givencolour point can also be determined graphically. Thewhite point is completely unsaturated (has no colour).The ratio of distances between the colour and the whitepoint and the pure colour and the white point gives ussaturation: saturation = |W-U| / |W-P| The saturation is always taken as 1 on the horseshoe (fully saturated) and zero at the white point. If weconsider a colour on the diagram at point [0.2, 0.3, 0.5] we can see that this ratio is approximately equal to0.4. This tells us the white content of the point. We can also determine a pure colour by considering theline through the point and the white point. From the slope of the line we can calculate that it cuts the y axisat [0, 0.25, 0.75]. This point is not in the visible region of the CIE diagram. The nearest pure colour will beseen to be around [0.04, .26, .736]. The complement of this colour can be found by determining the colourwhich when added to it will produce white. This will be on the z=0 line, and so we have that [0.04, .26,0.736] + [r,g,0] = [k,k,k] Solving for r and g we have first k = .736, whence 0.04 + r = 0.736, so r = 0.696and g = 0.476. If we normalise these points we get [0.6, 47 CU IDOL SELF LEARNING MATERIAL (SLM)

0.4, 0.0] as shown on the diagram. Notice that thenormalisation on the diagram gives a weighting to the colour coordinates. Since on the diagram the linejoining a colour and its complement always goes through the white point, it is always possible to find alinear combination of the two that produces white. It does not mean that adding the co-ordinates andnormalising produces white. Subtractive Colour Representation Paints and printing ink absorb colour reflecting only part of the incident light. For this reason they are called subtractive primaries The three principal colours of paints are magenta (purple), cyan (pale blue) and yellow. These three can be created by combining the additive colour primaries. Magenta is red and blue, cyan is blue and green, and yellow is red and green. Black is created by a blend of the three subtractive primaries, but is usually also used in colour printing for convenience. It reflects none of the incident light. White paint (or paper) reflects all the incident light and so does not change its colour. Black and white paints can be blended to produce different shades of grey. With grey and red paint you may make brown, and a milliard other colours which have no equivalents in the preceding systems. Paints are much richer than colours produced by red/green/blue lights. Figure 3.4 indicates how the different, pure basic colours are generated by the additive e (monitor) and subtractive (printer) colour systems. Figure 3.10: Colour Mixing Each circle represents one basic additive (R,G,B), or subtractive (M,C,Y) colour. The other regions indicate pure colours generated by two basic colour addition or subtraction, respectively. The centre colour (three addition or subtraction) in the additive system is white, while it is black in the subtractive system (all colours are absorbed). The two systems show additive or subtractive complementary colours in the same region; i.e., red + cyan light makes white while red + cyan paint makes black. 48 CU IDOL SELF LEARNING MATERIAL (SLM)

Practical Colours Approximately 128 different hues may be distinguished by the human eye. For each hue around 20 to 30 different saturation values may be seen as different colours. The eye is capable of distinguishing between 60 and 100 different brightness levels. If we multiply these three numbers, we get approximately 350,000 different colours. 24 bits provides us over 1.6 million colour shades, however, the eye is very sensitive to differences and under some circumstances small differences can be detected by it. Practical Colour Displays Color is an effective way of conveying information and it has important uses in tasks where identification, coding and response times are important. When a transformation is necessary from the CIE standard colour chart to the colour produced on a specific display device, we must express the primary colours of the display device by x and y quantities. Good quality monitors will be calibrated for the CIE colour chart. For example, a colour CRT monitor may have the following primary colour sources: Table 3.1: Practical colour displays These three points define a triangle on the CIE chromaticity diagram, as shown in the figure below. Only the points inside this triangle may be reproduced by the display device. 49 CU IDOL SELF LEARNING MATERIAL (SLM)

Figure 3.11: Display colours Colour Spaces and Transformation of Colours There are many different ways of representing colour, and often they can be expressed as linear combinations of each other. For example, the transformation from computer colour intensities R,G,B (expressed in the range from 0.0 to 1.0) may be done by the matrix The pure red on the monitor has representation of [1.0, 0, 0] which then produces the correct CIE values of [0.628, 0.346, 0.026] for the monitor. In order to find out how to represent a known CIE colour on the display, we have to invert the matrix and then right multiply it with the vector [x,y,z]. One useful colour space is called the HSI (Hue, Saturation and Intensity) space. It is of interestsince it is thought to correspond more closely to our perception of colour than the RGB space wehave been discussing.Note that, every colour in the RGB system is made up of a white component whose magnitude isthe minimum out of r g and b, and a pure colour defined by the ratio of the two non-zero colourswhen the white component has beensubtracted. 50 CU IDOL SELF LEARNING MATERIAL (SLM)