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Arignar Anna Government Arts & Science College Karaikal, Puducherry (U.T), Affiliated to Pondicherry University Department of Computer Science
COMPUTER GRAPHICS
Paper Code: 249
MODULE - I
Overview of Computer Graphics System: Video Display Devices – Raster Scan Systems – Random – Scan Systems - Graphics Monitors and Workstations – Input Devices – Hardcopy Devices – Graphics Software.
MODULE - II
Output Primitives: Line Drawing Algorithms – Loading the Frame Buffer – Line Function – Circle – Generating Algorithms - Attributes of Output Primitives: Line Attributes – Curve Attributes – Color and Gray scale levels– Area fill Attributes – Character Attributes – Bundled Attributes – Inquiry Functions.
MODULE - III
2D Geometric Transformations: Basic Transformation – Matrix Representations – Composite Transformations – Window to View port Co-Ordinate Transformations - Clipping: Point Clipping – Line Clipping – Cohen-Sutherland Line Clipping – Liang Barsky Line Clipping – Polygon Clipping – Sutherland
- Hodgeman Polygon Clipping – Curve Clipping – Text Clipping.
MODULE - IV
Graphical User Interfaces and Interactive Input Methods: The User Dialogue – Input of Graphical Data – Input Functions – Interactive Picture Construction Techniques – Three Dimensional Concepts: 3D-Display Methods – Three Dimensional Graphics Packages
MODULE - V
3D Geometric and Modeling Transformations: Translation – Scaling – Rotation – Other Transformations. Visible Surface Detection Methods: Classification of Visible Surface Detection Algorithm – Back face Detection – Depth-Buffer Method – A Buffer Method – Scan-Line Method – Applications of Computer Graphics.
Text Book: Donald Hearn M. Pauline Baker, Computer Graphics C Version, 2nd edition, Pearson Education, 2014.
MODULE - I
Overview of Computer Graphics System: Video Display Devices – Raster Scan Systems – Random – Scan Systems - Graphics Monitors and Workstations – Input Devices – Hardcopy Devices – Graphics Software.
Overview of Computer Graphics System
Computer graphics is commonly seen as a computer science branch that deals with the computerized image fusion theory and technology. As simple as a triangle outline, a computer-generated image may represent a scene. The computer has become a powerful tool for producing images quickly and economically.
When a computer is used to create images, the same process is followed as creating images manually. The process’s primary computational steps give a boost to several important computer graphics areas.
Also on computers, the term computer graphics covers almost everything. Here in the computer graphics program’s classroom, we think of computer graphics as drawing images on machines, often known as rendering. The images can be photos, sketches, animations, or pictures of items imagined. Or they may be pictures, we cannot see directly, like internal body parts.
We have put a great deal of our time to develop how computer images can replicate real-world scenes. We want objects on computers not only to look more real, but also their colors to be more realistic and how different materials appear. We can call it “real synthesis of the image.”
The term computer graphics has been used to define “almost everything on the computer, including text or sound.” Generally, the term computer graphics refer to the following things:
Computer representation and manipulation of image data. Various technologies for creating and manipulating images. Computer graphics study is a sub-field of computer science that studies methods for digitally incorporating and manipulating visual content.
The next area of computer graphics that deals with the placement of a triangle is called transformation. Here we can use matrices to get the mapping of a triangle in image space. We can also set up the transformation matrix to control the location and orientation of the displayed image. We can also resize the triangle.
Display controller or video controller Digital memory or frame buffer Television monitor
1. Display controller or video controller- It’s a Memory Buffer and TV Monitor interface. Its task is to pass Frame Buffer’s contents to the monitor. The display controller reads each continuous byte of Memory frame buffer data and converts 0’s and 1’s into appropriate video signals.
In today’s term, the display controller is recognized as a display card, and one of our choices can be a VGA(Video Graphics Array) card with a resolution of 640×480. Display Controller is also capable of displaying the image in colors.
2. Digital memory or frame buffer -This is a place where images and pictures are stored as an array (matrix of 0 & 1, 0 represents darkness, and 1 represents image or picture). It is also called a frame buffer.
In today’s term frame buffer is called V-RAM (video RAM), and it helps to store the image in bit form. It helps to increase the speed of graphics.
3. Television monitor- Monitor helps us to view the display, and they make use of CRT(Cathode ray tube) technology.
Advantages
- Superior Quality.
- More accurate outcomes or products.
- Increased Productivity.
- Lower cost of development.
- Increases the ability to understand information and interpret patterns significantly.
Non- Interactive Computer Graphics
Non-interactive computer graphics are also known as passive computer graphics. It is a type of computer graphics in which the user has no control over the image. The photo is completely controlled by the instructions of the program, not by the user.
For Example:
Screen savers. Map representation of the data. Graphic elements are used in the text, document, and PDF presentation. Static images are used in mobile applications and websites. Business graphics are used as brochures, business cards, menu of the hotel.
Representation of graphics
We can represent the graphics by following two ways:
- Raster (Bitmap) Graphics
- Vector Graphics 1. Raster Graphics: In raster graphics, the image is presented as a rectangular grid of colored squares.
Raster images are also called bitmap images. Bitmap images are stored as the collection of small individual dots called pixels.
Bitmap images require high resolution and anti-aliasing for a smooth appearance.
For example – Paint, Photoshop, etc.
2. Vector Graphics: In vector graphics, the image is represented in the form of continuous geometric objects: line, curve, etc.
Vector images are not based on pixel pattern. They use mathematical formulas to draw line and curves. The lines and curves can be combined to create an image.
For Example – PowerPoint, Corel Draw, etc.
Fig: Raster (Composition of Paths) Vector (Composition of Pixels)
Horizontal & Vertical Deflection Plates: These plates are used to guide the path of the electron the beam. The plates produce an electromagnetic field that bends the electron beam through the area as it travels. Phosphorus-coated Screen: The phosphorus coated screen is used to produce bright spots when the high-velocity electron beam hits it.
The main element of a video monitor is the Cathode Ray Tube CRT , shown in the following illustration.
The operation of CRT is very simple −
The electron gun emits a beam of electrons cathode rays. The electron beam passes through focusing and deflection systems that direct it towards specified positions on the phosphor-coated screen. When the beam hits the screen, the phosphor emits a small spot of light at each position contacted by the electron beam. It redraws the picture by directing the electron beam back over the same screen points quickly.
There are two ways Random scan and Raster scan by which we can display an object on the screen.
Raster Scan
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.
Picture definition is stored in memory area called the Refresh Buffer or Frame Buffer. This memory area holds the set of intensity values for all the screen points. Stored intensity values are then retrieved from the refresh buffer and “painted” on the screen one row scan line at a time as shown in the following illustration.
Each screen point is referred to as a pixel picture element or pel. 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.
Random Scan /Vector Scan
In this technique, the electron beam is directed only to the part of the screen where the picture is to be drawn rather than scanning from left to right and top to bottom as in raster scan. It is also called vector display, stroke-writing display, or calligraphic display.
Picture definition is stored as a set of line-drawing commands in an area of memory referred to as the refresh display file. To display a specified picture, the system cycles through the set of commands in the display file, drawing each component line in turn. After all the line-drawing commands are processed, the system cycles back to the first line command in the list.
Random-scan displays are designed to draw all the component lines of a picture 30 to 60 times each second.
Application of Computer Graphics
Computer Graphics has numerous applications, some of which are listed below −
Computer graphics user interfaces GUIs − A graphic, mouse-oriented paradigm which allows the user to interact with a computer. Business presentation graphics − "A picture is worth a thousand words".
Disadvantages:
- Only four possible colors
- Time Consuming
2.Shadow – Mask Method: It is used with a raster scan monitor for displaying pictures. It has more range of color than the beam penetration method. It is used in television sets and monitors.
Structure:
- It has three phosphorus color dots at each position of the pixel.
First Dot: Red color Second Dot: Green color Third Dot: Blue color
- It has three different guns. Each for one color.
- It has a metal screen or plate just before the phosphorus screen, named “Shadow-Mask.”
- It also has a shadow grid just behind the phosphorus coated screen with tiny holes in a triangular shape.
Working: A Shadow Mask is a metal plate with tiny holes present inside a color monitor.
A Shadow Mask directs the beam by consuming the electrons so that the beam hits only the desired point and displays a resulting picture.
It has three different guns. These guns direct their beams to shadow mask, which allows them to pass. It is a task of a shadow mask to direct the beam on its particular dot on the screen and produce a picture on the screen.
A Shadow Mask can display a wider range of pictures than beam penetration.
Advantages:
- Display a wider range picture.
- Display realistic images.
- In-line arrangement of RGB color.
Disadvantages:
Difficult to cover all three beams on the same hole. Poor Resolution.
Liquid crystal display (LCD): The LCD depends upon the light modulating properties of liquid crystals. LCD is used in watches and portable computers. LCD requires an AC power supply instead of DC, so it is difficult to use it in circuits. It generally works on flat panel display technology. LCD consumes less power than LED. The LCD screen uses the liquid crystal to turn pixels on or off. Liquid Crystals are a mixture of solid and liquid. When the current flows inside it, its position changes into the desired color.
For Example: TFT(Thin Film Transistor)
Advantages:
- Produce a bright image
- Energy efficient
- Completely flat screen
Disadvantages:
- Fixed aspect ratio & Resolution
- Lower Contrast
- More Expensive
Light Emitting Diode (LED): LED is a device which emits when current passes through it. It is a semiconductor device. The size of the LED is small, so we can easily make any display unit by arranging a large number of LEDs. LED consumes more power compared to LCD. LED is used on TV, smartphones, motor vehicles, traffic light, etc. LEDs are powerful in structure, so they are capable of withstanding mechanical pressure. LED also works at high temperatures.
Advantages:
- The Intensity of light can be controlled.
- Low operational Voltage.
- Capable of handling the high temperature.
Disadvantages:
More Power Consuming than LCD.
Advantages:
- Wall Mounted
- Slim
- Wider angle
Disadvantages:
- Phosphorus loses luminosity over time.
- It consumes more electricity than LCD.
- Large Size
3D Display: It is also called stereoscope display technology. This technology is capable of bringing depth perception to the viewer. It is used for 3D gaming and 3D TVs.
For Example: Fog Display, Holographic Display, Retina Display Etc.
Advantages:
Impressive Picture Quality High Definition Motion Communicates
Disadvantage:
Expensive Binocular Fusion
Input Devices
Following are some of the important input devices which are used in a computer −
Keyboard Mouse
Joy Stick Light pen Track Ball Scanner Graphic Tablet Microphone Magnetic Ink Card Reader(MICR) Optical Character Reader(OCR) Bar Code Reader Optical Mark Reader(OMR)
Keyboard
Keyboard is the most common and very popular input device which helps to input data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.
Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.
The keys on the keyboard are as follows −
S.No Keys & Description
Typing Keys
These keys include the letter keys (A-Z) and digit keys (09) which generally give the same layout as that of typewriters.
Numeric Keypad
It is used to enter the numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
The function of the joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing (CAD) and playing computer games.
Light Pen
Light pen is a pointing device similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube.
When the tip of a light pen is moved over the monitor screen and the pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.
Track Ball
Track ball is an input device that is mostly used in notebook or laptop computer, instead of a mouse. This is a ball which is half inserted and by moving fingers on the ball, the pointer can be moved.
Since the whole device is not moved, a track ball requires less space than a mouse. A track ball comes in various shapes like a ball, a button, or a square.
Scanner
Scanner is an input device, which works more like a photocopy machine. It is used when some information is available on paper and it is to be transferred to the hard disk of the computer for further manipulation.
Scanner captures images from the source which are then converted into a digital form that can be stored on the disk. These images can be edited before they are printed.
Digitizer
Digitizer is an input device which converts analog information into digital form. Digitizer can convert a signal from the television or camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at.
Digitizer is also known as Tablet or Graphics Tablet as it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for fine works of drawing and image manipulation applications.
Microphone
Microphone is an input device to input sound that is then stored in a digital form.
The microphone is used for various applications such as adding sound to a multimedia presentation or for mixing music.
Magnetic Ink Card Reader (MICR)
MICR input device is generally used in banks as there are large number of cheques to be processed every day. The bank's code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable.
Optical Mark Reader (OMR)
OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked.
It is specially used for checking the answer sheets of examinations having multiple choice questions.
Output Devices
An output device is a component of hardware or the main physical part of a computer that can be touched and seen. An output device is an electromechanical device.
“The Computer gives instructions and data from input devices and processes it and returns the result called as output.”
For Example: Printer, Plotter, Monitor, Projector etc.
Printers:
A printer is a peripheral device which is used to represent the graphics or text on paper. The quality is measured by its resolution. The resolution of any printer is measured in dot per inch (dpi).
The printer usually works with the computer and connected via a cable. In present, many digital device support printer features so that we can use Bluetooth, Wi-fi, and cloud technology to print.
Types of Printers
Some types of printers are:
Impact Printers Non-impact Printers
Impact Printers
In impact printers, there is a physical contact established between the print head, ribbon, ink-cartridge, and paper.
The printers hit print head on an ink-filled ribbon than the letter prints on the paper. Impact printers are works like a typewriter.
Impact printers print the characters by striking them on the ribbon, which is then pressed on the paper.
Characteristics of Impact Printers are the following −
Very low consumable costs Very noisy Useful for bulk printing due to low cost There is physical contact with the paper to produce an image
These printers are of two types −
Character printers Line printers
Character Printers
Character printers are the printers which print one character at a time.
These are further divided into two types:
Dot Matrix Printer(DMP) Daisy Wheel
Dot Matrix Printer
In the market, one of the most popular printers is Dot Matrix Printer. These printers are popular because of their ease of printing and economical price. Each character printed is in the form of pattern of dots and head consists of a Matrix of Pins of size (57, 79, 97 or 99) which come out to form a character which is why it is called Dot Matrix Printer.
