Computer Graphics

BON SECOURS COLLEGE FOR WOMEN
DEPARTMENT OF COMPUTER APPLICATIONS

Objective:
MAJOR BASED ELECTIVE- COMPUTER
GRAPHICS
To understand the concepts on basic Graphical Techniques, Raster Graphics, Two Dimensional
and Three Dimensional Graphics
Unit 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.
Unit 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
Grayscale levels– Area fill Attributes – Character Attributes – Bundled Attributes – Inquiry Functions.
Unit 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 – Hodgman Polygon Clipping – Curve Clipping – Text Clipping.
Unit 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
Unit V
3D Geometric and Modeling Transformations: Translation – Scaling – Rotation – Other
Transformations.Visible Surface Detection Methods: Classification of Visible Surface Detection
Algorithm –Backface Detection – Depth-Buffer Method – A-Buffer Method –Scan-Line Method –
Applications of Computer Graphics.
Text Book:
1. Donald Hearn M. Pauline Baker, Computer Graphics C Version, Second Edition,
Pearson Education, 2014.

1. OVERVIEW OF GRAPHICS SYSTEMS
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Definition:
Computer graphics is an art of drawing pictures on computer screens with the help of
programming. It involves computations, creation, and manipulation of data. Computer graphics is a
rendering tool for the generation and manipulation of images.
In other words, we can say that it is a visual representations of data displayed on a monitor. It can
be a series of images (most often called video) or a single image. It is used for making movie, video game,
scientific modeling, design for catalogs and other commercial art.
Classification of Computer Graphics:
Computer graphics as drawing pictures on computers, also called rendering. 2D computer
graphics are usually split into two categories:
1. Vector Graphics
2. Raster graphics
Vector Graphics
Vector graphics is the creation of digital images through a sequence of commands or
mathematical statements.
In Vector graphics lines, shapes, and text are used to create a more complex image.
Vector graphics are made with programs like Adobe Illustrator and Inkscape etc…
Vector graphics image is shown in Fig 1.1.
Raster Graphics
Raster Graphics or Bitmap Image is a dot matrix data structure, representing rectangular grid of
pixels, or points of color.
Raster images are stored in image files with varying formats.
Raster graphics use pixels to make up a larger image.
Raster programs are made by Paintbrushes Adobe Photoshop and Corel Paint Shop Pro.
Sometimes people do use only pixels to make an image. This is called pixel art and it has a very
unique style. Raster image is shown in Fig 1.2.

Fig 1.1 Vector Image Fig 1.2 Raster Image

VIDEO DISPLAY DEVICES:
The primary output device in a graphics system is a video monitor is shown in Fig 1.3. The
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operation of most video monitors is based on the standard cathode-ray tube (CRT) design.
Refresh Cathode-Ray Tubes
● A beam of electrons (cathode rays), emitted by an electron gun, passes through focusing and
deflection systems that direct the beam toward specified positions on the phosphor-coated
screen.
Fig 1.3 computer graphics workstation
The phosphor then emits a small spot of light at each position contacted by the electron beam.
Figure 1.4 Basic design of a magnetic deflection CRT
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.
The primary components of an electron gun in a CRT are the heated metal cathode and a control

grid (Fig.1.5).
Heat is supplied to the cathode by directing a current through a coil of wire, called the filament.
This causes electrons to be 'boiled off" the hot cathode surface. In the vacuum inside the CRT
envelope, the free, negatively charged electrons are then accelerated toward the phosphor coating
by a high positive voltage.

Sometimes the electron gun is built to contain the accelerating anode and focusing system within
the same unit. 5
Fig 1.5 Operation of an electron gun with an accelerating anode
Intensity of the electron beam is controlled by setting voltage levels on the control grid, which is
a metal cylinder that fits over the cathode.
A high negative voltage applied to the control grid will shut off the beam by repelling electrons; a
smaller negative voltage on the control grid simply decreases the number of electrons passing
through.
The amount of light emitted by the phosphor coating depends on the number of electrons striking
the screen.
The focusing system in a CRT is needed to force the electron beam to converge into a small spot
as it strikes the phosphor.
Focusing is accomplished with either electric or magnetic fields. Electrostatic focusing is
commonly used in television and computer graphics monitors.
Additional focusing hardware is used in high precision systems to keep the beam in focus at all
screen points.
Deflection of the electron beam can be controlled either with electric fields or with magnetic
fields. Cathode ray tubes are constructed with magnetic deflection coils mounted on the outside of
the CRT envelope.
Two pairs of coils are used, with the coils in each pair mounted on opposite sides of the neck of
the CRT envelope.

One pair is mounted on the top and bottom of the neck and the other pair is mounted on opposite
sides of the neck.
Horizontal deflection is accomplished with one pair of coils, and vertical deflection by the other
pair.
One pair of plates is mounted horizontally to control the vertical deflection, and the other pair is
mounted vertically to control horizontal deflection (Fig 1.6).

Persistence:
Persistence means how long the phosphors continue to emit light after the CRT beam is removed.
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A phosphor with low persistence is useful for animation.
A higher persistence phosphor is useful for displaying highly complex, static pictures.
Fig 1.6 Electrostatic deflection of the electron beam in a CRT
Resolution:
Resolution is the number of pixels contained on a display monitor, expressed in terms of the
number of pixels on the horizontal axis and vertical axis.
It can be also referred as maximum number of points that can be displayed without overlap on a
CRT.
The sharpness of the image on a display depends on the resolution and the size of the monitor.
Aspect ratio:
The ratio of vertical points to the horizontal points necessary to produce length of lines in both
directions of the screen is called the aspect ratio.
An aspect ratio of ¾ means that a vertical line plotted with three points has the same length as a
horizontal line plotted with four points.
Raster-Scan Displays
Common type of graphics monitor employing a CRT is the raster-scan display, based on
television technology.

Fig. 1.7 Raster Scan System displays

In a raster-scan system, the electron beam is swept across the screen, one row at a time from top
to bottom. 7
The electron beam moves across each row, the beam intensity is turned on and off to create a
pattern of illuminated spots.
Refresh Buffer or Frame Buffer
Picture definition is stored in a memory area called the refresh buffer or frame buffer.
Scan Line
The frame buffer 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 at a time is called scan line
(Fig. 1.7).
Pixel
Each screen point is referred to as a pixel or pel or picture element.
Intensity range for pixel positions depends on the capability of the raster system.
In a simple black-and-white system, each screen point is either on or off. So only one bit per
pixel is needed to control the intensity of screen positions.
For a bi-level system, a bit value of 1 indicates that the electron beam is to be turned on at that
position, and a value of 0 indicates that the beam intensity is to be off.
Bitmap
bitmap.
Pixmap
On a black-and-white system with one bit per pixel, the
frame buffer is commonly called a
Systems with multiple bits per pixel, the frame buffer is often referred to as a pixmap.
Refreshing on raster scan displays is carried out at the rate of 60 to 80 frames per second. Refresh
rates are described in units of cycles per second or Hertz.
Using these units, we would describe a refresh rate of 60 frames per second as simply 60 Hz.
Horizontal Retrace
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

of the electron beam.
Vertical Retrace
At the end of each frame the electron beam returns to the top left corner of the screen to begin
the next frame is called vertical retrace.

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Fig 1.8 Interlacing scan lines on a Raster Scan Display
Interlace
Each frame is displayed in two passes using an interlaced refresh procedure.
In the first pass, the beam sweeps across every other scan line from top to bottom.
Then after the vertical retrace, the beam sweeps out the remaining scan lines (Fig 1.8).
Random-Scan Displays
In a random-scan display unit, a CRT has the electron beam directed only to the parts of the
screen where a picture is to be drawn (Fig 1.9).
Random-scan monitors draw a picture one line at a time and for this reason are also referred to as
vector displays or stroke-writing or calligraphic displays.
Refresh rate on a random-scan system depends on the number of lines to be displayed.
Fig. 1.9 Raster Scan System displays
Refresh Display File
Picture definition is now stored as a set of line-drawing commands in an area of memory referred
to as the refresh display file.
It is called the display list, display program, or simply the refresh buffer.
Random-scan displays are designed to draw all the component lines of a picture 30 to 60 times
each second.

High-quality vector systems are capable of handling approximately 100,000 "short" lines at this
refresh rate.
Random-scan systems are designed for line-drawing applications and cannot display realistic
shaded scenes.

Color CRT Monitors
A CRT monitor displays colour pictures by using a combination of phosphors that emit different-
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colored light. By combining the emitted light from the different phosphors, a range of colors can be generated.
The two basic techniques for producing color displays.
1. Shadow-mask method.
2. Beam-Penetration Method
Beam-Penetration Method
In beam-penetration method two layers of phosphor, usually red and green, are coated onto the
inside of the CRT screen.
The displayed color depends on how far the electron beam penetrates into the phosphor layers.
A beam of slow electrons excites only the outer red layer.
A beam of very fast electrons penetrates through the red layer and excites the inner green layer.
At intermediate beam speeds, combinations of red and green light are emitted to show two
additional colors, orange and yellow.
Shadow-mask method
Shadow-mask methods are commonly used in raster scan systems because they produce wider
range of colors than the beam penetration method.
A shadow-mask CRT has three phosphor color dots at each pixel position.
One phosphor dot emits a red light, another emits a green light, and the third emits a blue light.
This type of CRT has three electron guns, one for each color dot, and a shadow-mask grid just
behind the phosphor-coated screen.
Types of Shadow-mask:
There are two types of shadow mask
1. Delta – delta Shadow mask
2. Inline shadow mask

Fig 1.10 Operation of a delta-delta, shadow mask CRT

Delta –delta shadow mask method are used in color CRT systems. Three electron beams are deflected
and focused, which contains a series of holes aligned with the phosphor dot patterns
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(Fig 1.10).
When three beams pass through a hole in the shadow mask, they activate a dot triangle color spot
on the screen.
Another arrangement for the electron gun is an in-line arrangement in which the three electron
guns and the corresponding red-green-blue color dots on the screen are aligned in one scan line
instead of triangular pattern.
These in line arrangement of electron guns are used in high resolution color CRT.
Full Color System or True Color System
An RGB color system with 24 bits of storage per pixel is generally referred to as a full-color
system or a true-color system.
Direct-View Storage Tubes
It stores the picture information inside the CRT instead of refreshing the screen. Two electron
guns are used in a DVST.
1. Primary Gun
2. Flood Gun
The primary gun is used to store the picture pattern. The second, the flood gun, maintains the
picture display. The DVST has both advantages and disadvantages compared to refresh CRT.
Advantages
No refreshing is needed; very complex pictures can be displayed at very high resolutions without
flicker.
Disadvantages
They do not display color and that selected parts of a picture cannot be erased.
To eliminate a picture section, the entire screen must be erased. Erasing and redrawing process
can take several seconds for a complex picture.
Flat-Panel Displays
The term flat-panel display refers to a class of video devices that have reduced volume, weight,
and power requirements compared to a CRT.
A significant feature of flat-panel displays is that they are thinner than CRTs, and we can hang
them on walls or wear them on our wrists.

Current uses for flat-panel displays include small TV monitors, calculators, pocket video games,
laptop computers, etc.,
There are two categories:
⮚ Emissive displays or Emitters
⮚ Non emissive displays or non emitters

1. Emissive displays or Emitters
The emissive displays devices that convert electrical energy into light. Plasma panels, thin-film
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electroluminescent displays and light emitting diodes are examples of emissive displays.
Plasma panels:
▪ It is also called gas –discharge displays, are constructed by filling the region between two glass
plates with mixture of gases, usually includes neon.
▪ A series of vertical conducting ribbons is placed on one glass panel, and set of horizontal ribbons
is built into other glass panel.
▪ Firing voltage is applied to a pair of horizontal and vertical conductors, the gas at the intersection
of two conductors break down into glowing plasma of electrons and ions.
▪ Picture definition is stored in a refresh buffer, and the firing voltages are applied to refresh the
pixel positions 60 times per second. Alternating current methods are used to provide faster
application of firing voltages and brighter displays.
Disadvantages:
Plasma panel only applicable for monochromatic devices, but systems have been developed for
displaying color and grayscale.
Thin-Film Electroluminescent Displays:
▪ The construction of Thin-Film Electroluminescent Displays is similar to plasma panel.
▪ But the difference is that the region between the glass plates is filled with a phosphor such as
Zinc sulphide doped with manganese, instead of gas.
▪ When high voltage is applied to a pair of electrodes, electrical energy is absorbed by manganese
atoms then release the spot of light similar to plasma panel.
▪ It is more powerful than plasma panel and produce good color and gray scale.
LED (Light –emitting diode):
▪ A matrix of diodes is arranged to form the pixel positions in the display, and picture definition is
stored in a refresh buffer.
▪ Information is read from the refresh buffer and converted to voltage that is applied to the diodes
into light pattern in the display.

2. Non emissive displays or non emitters
Non emissive displays use optical effects to convert sunlight or light from some other source into
graphics patterns.
Example: LCD
▪ Liquid-crystal displays (LCDS) are commonly used in small systems, such as calculators and
portable, laptop computers.
▪ Each pixel of an LCD consists of a layer of molecules aligned between two transparent electrodes
with light polarizer.

▪ Passive-matrix LCD is an LCD technology that uses a grid of vertical and horizontal conductors
comprised of Indium Tin Oxide (ITO) to create an image. 12
▪ Another method for constructing LCD is to place a transistor at each pixel position, using thin
film transistor technology. The transistors are used to control the voltage at pixel locations are
called active matrix displays.
RASTER-SCAN SYSTEM:
In raster graphics, in addition to the central processing unit, or CPU, a special-purpose processor,
called the video controller or display controller, is used to control the operation of the display device.
Organization of a simple raster system in shown in Fig.1.11.
Fig 1.11 Architecture of a simple raster system
Video Controller
Fig 1.12 Architecture of raster system with a fixed portion of the system memory
A fixed area of the system memory is reserved for the frame buffer. So the video controller is
given direct access to the frame-buffer memory (Fig 1.12).
Frame-buffer locations, and the corresponding screen positions, are referenced in Cartesian
coordinates. The coordinate origin is defined at lower left screen corner.
▪ Then the first quadrant of a two dimensional system, positive x values increasing to the right and
positive y values increasing from bottom to top.
▪ Scan lines are labeled from ymax at the top of the screen to 0 at the bottom, each scan line screen

pixel positions are labeled from 0 to xmax.

▪ There are two registers are used to store the coordinates of the screen pixels.
▪ Initially, the x register is set to 0 and the y register is set to ymax.
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▪ The value stored in the frame buffer for this pixel position is then retrieved and used to set the
intensity of the CRT beam.
▪ Then the x register is incremented by 1, and the process repeated for the next pixel on the top
scan line.
▪ In high quality system, two frame buffers are provided, one for refreshing other for filling
intensity values.
Raster-Scan Display Processor
A raster system containing a separate display processor, sometimes referred to as a graphics
controller or a display coprocessor (Fig 1.13).
Scan Conversion
▪ 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.
▪ Display processors are also designed to perform a number of additional operations.
▪ These functions include generating various line styles (dashed, dotted, or solid), displaying color
areas, and performing certain transformations and manipulations on displayed objects.
Fig 1.13 Raster Graphics System with Display Processor
Run Length Encoding
▪ Intensity information is to store each scan line as a set of integer pairs.
▪ One number of each pair indicates an intensity value, and the second number specifies the

number of adjacent pixels on the scan line.
▪ This technique, called run-length encoding.
Cell Encoding
It is another approach to encode the raster as a set of rectangle areas called cell encoding.

RANDOM SCAN SYSTEMS
The organization of simple random scan system is shown in Fig 1.14.
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▪ An application program is input and is stored in the system memory.
▪ Graphics commands in the application 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 in a random-scan system is referred to as a display processing unit or a
graphics controller.
Fig 1.14 Architecture of simple Random Scan System
GRAPHICS MONITORS AND WORKSTATIONS
▪ Graphics systems are designed as small general-purpose computer systems with graphics
capabilities.
▪ Full-color systems that are designed specifically for graphics applications.
▪ High-definition graphics monitor used in applications such as air traffic control, simulation,
medical imaging, and CAD.
▪ This system has a diagonal screen size of 27 inches, resolutions ranging from 2048 by 1536 to
2560 by 2048, with refresh rates of 80 Hz or 60 Hz non interlaced.
▪ Workstation refers to any computer device or program that makes a computer capable of
displaying and manipulating pictures.

Fig 1.15 General Purpose Computer System that can be used for Graphics Application
For example, laser printers and plotters are graphics devices because they permit the computer to
output pictures.

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1.16 Computer Graphics Workstations
INPUT DEVICES
Keyboard
▪ The keyboard helps in inputting the data to the computer.
▪ The layout of the keyboard is like that of traditional typewriter, although there are some
additional keys provided for performing some additional functions.
▪ Keyboards are of two sizes 84 keys or 101/102 keys, but now 104 keys or 108 keys keyboard is
also available for Windows and Internet.
Fig 1.17 Keyboard
Mouse
▪ Mouse is most popular Pointing device.
▪ It is a very famous cursor-control device. It is a small palm size box with a round ball at its base
which senses the movement of mouse and sends corresponding signals to CPU on pressing the
buttons.
▪ Generally, it has two buttons called left and right button and scroll bar is present at the mid.
Mouse can be used to control the position of cursor on screen, but it cannot be used to enter text
into the computer.
Advantages
⮚ Easy to use
⮚ Not very expensive

⮚ Moves the cursor faster than the arrow keys of keyboard
Joystick
▪ Joystick is also a pointing device, which is used to move cursor position on a monitor screen.
▪ It is a stick having a spherical ball at its both lower and upper ends.

▪ The lower spherical ball moves in a socket
▪ The joystick can be moved in all four directions. 16
▪ It is mainly used in Computer Aided Designing (CAD) and playing computer games.
Fig 1.18 Joystick Fig 1.19 Light pen
Light Pen
▪ Light pen is a pointing device, which is 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 light pen's tip is moved over the monitor screen and 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 ball, 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 and a square.
Fig 1.20 Track Ball Fig 1.21 Scanner
Scanner

▪ Scanner is an input device, which works more like a photocopy machine.
▪ It is used when some information is available on a paper and it is to be transferred to the hard
disc of the computer for further manipulation.
▪ Scanner captures images from the source which are then converted into the digital form that can
be stored on the disc.
▪ These images can be edited before they are printed.

Digitizer
▪ Digitizer is an input device, which converts analog information into a digital form.
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▪ Digitizer can convert a signal from the television 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 because it converts graphics and pictorial
data into binary inputs.
Fig 1.22 Digitizer
Bar Code Readers
▪ Bar Code Reader is a device used for reading bar coded data. Bar coded data is generally used in
labelling goods, numbering the books, etc.
▪ It may be a hand-held scanner or may be embedded in a stationary scanner.
Fig 1.23 Barcode Readers
▪ Bar Code Reader scans a bar code image, converts it into an alphanumeric value, which is then
fed to the computer to which bar code reader is connected.
HARD COPY DEVICES
▪ To a obtain hard-copy output for our images in several formats.

▪ For presentations or archiving, we can send image files to devices or service bureaus that will
produce 35-mm slides or overhead transparencies.
▪ We can put our pictures on paper by directing graphics output to a printer or plotter.
▪ The quality of the pictures obtained from a device depends on dot size and the number of dots
per inch, or lines per inch, that can be displayed.

Printers
Printer is the most important output device, which is used to print information on paper.
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There are two types of printers:
1 Impact Printers
2 Non-Impact Printers
▪ These printers use non-Impact technology such as ink-jet or laser technology.
▪ These printers provide better quality of O/P at higher
speed. There are two types:
1. Ink-Jet Printer
2. Laser Printer

Ink-Jet Printer:
▪ It prints characters by spraying patterns of ink on the paper from a nozzle or jet.
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▪ It prints from nozzles having very fine holes, from which a specially made ink is pumped out to
create various letters and shapes.
Laser Printer:
▪ It is a type of printer that utilizes a laser beam to produce an image on a drum.
▪ This is also the way copy machines work. Because an entire page is transmitted to a drum before
the toner is applied, laser printers are sometimes called page printers.
GRAPHICS SOFTWARE
There are two general classifications for graphics software:
General Programming Packages
A general graphics programming package provides an extensive set of graphics functions that can
be used in a high-level programming language, such as C or FORTRAN.
Example: Generating picture components straight lines, polygons, circles, and other figures.
Special-Purpose Applications Packages
Application graphics packages are designed for nonprogrammers, so that users can generate
displays without worrying about how graphics operations work.
Example: Artist’s painting programs and various business, medical, and CAD systems
Coordinate Representations
▪ Coordinate values for a picture are converted to Cartesian coordinates before they can be input to
the graphics package.
▪ Different Cartesian reference frames are used to construct and display a scene.
Modeling Coordinates
▪ We can construct the shape of individual objects, such as trees or furniture, in a scene within
separate coordinate reference frames called modeling coordinates, or sometimes local coordinates
or master coordinates.
World Coordinates
Once individual object shapes have been specified, we can place the objects into appropriate
positions within the scene using a reference frame called world coordinates.
Graphics Functions

▪ A general-purpose graphics package provides users with a variety of functions for creating and
manipulating pictures.
▪ The basic building blocks for pictures are referred to as output primitives. They include character
strings and geometric entities, such as points, straight lines, curved lines, filled areas (polygons,
circles, etc.).

▪ Attributes are the properties of the output primitives. It includes intensity and color
specifications, line styles, text styles, and area-filling patterns. 20
Geometric Transformations
To change the size, position, or orientation of an object within a scene using
geometric transformations.
Modeling Transformations
It is used to construct a scene using object descriptions given in modeling coordinates
Viewing Transformations
▪ Viewing transformations are used to specify the view that is to be presented and
the portion of the output display area that is to be used.
▪ Pictures can be subdivided into component parts, called structures or
segments or objects, depending on the software package in use
▪ Interactive graphics applications use various kinds of input devices, such as a
mouse, a tablet, or a joystick.
Software Standards
▪ The primary goal of standardized graphics software is portability.
▪ When packages are designed with standard graphics functions, software can he
moved easily from one hardware system to another and used in different
implementations and applications.
Graphical Kernel System (GKS)
▪ It is the first graphics software standard by the International Standards Organization
(ISO).
▪ It is also includes in the American National Standards Institute (ANSI).
PHIGS (Programmer's Hierarchical Interactive Graphics standard)
▪ It is the second software standard to be developed and approved by the
standards organizations.It is an extension of GKS.
PHIGS Workstations
▪ Workstation refers to a computer system with a combination of input and output
devices that is designed for a single user.

▪ In PHIGS and GKS, however, the term workstation is used to identify
various combinations of graphics hardware and software.
▪ A PHIGS workstation can be a single output device, a single input device, a
combination of input and output devices, a file, or even a window displayed on
a video monitor.

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