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SYLLABUS
Unit-1: Brief Survey of Computer Graphics – Graphics Systems: Video Display Devices – Types –
Raster-Scan Systems and Random-Scan Systems – Input Devices – Hard-Copy Devices – Graphics
Software
Unit-2​​: Line-Drawing (DDA and Bresenham’s) Algorithms – Circle-Generating (Midpoint)
Algorithm – Ellipse-Generating (Midpoint) Algorithms – Area-Filling (Boundary-Fill and
Flood-Fill) Algorithms - Line Attributes - Color and Grayscale Levels – Character Attributes –
Inquiry Functions
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Basics Transformations
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Clipping Algorithm: Cohen Sutherland Line Clipping, Sutherland Hodgeman Polygon
Clipping Basic Modeling concepts
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Interactive Picture Construction Techniques
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Unit-5 : Viewing Pipeline and Coordinates – Transformation from World to Viewing Coordinates –
Projection Transformations - Matrices - View Volumes - Hidden Surface and Hidden Line
Elimination Methods: Back-Face Detection , Depth-Buffer and A-Buffer Methods – -Wireframe
Methods
1
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Hearn and M
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Baker, 2005, Computer Graphics , C Version,2​nd Edition ,Pearson
Education , New Delhi

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Reference Books

1)
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M
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F
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Ltd
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P
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Ltd
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3) N
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Ltd
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F
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Ltd
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A
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Unit-1: Brief Survey of Computer Graphics – Graphics Systems: Video Display Devices – Types –
Raster-Scan Systems and Random-Scan Systems – Input Devices – Hard-Copy Devices – Graphics
Software

COMPUTER GRAPHICS
1) Brief History of Computer Graphics
1
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It involves computations, creation, and manipulation of data
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Mathematics+ Computer Science+ Art=Computer graphics
2
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Common Graphics Languages
●
●
●
●
●

GKS
DirectX
X
Postscript
OpenGL

4
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● Business presentation graphics​​ − "A picture is worth a thousand words"
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● Weather Maps​​ − Real-time mapping, symbolic representations
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Photo Enhancement​​ − Sharpening blurred photos
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- Non-invasive internal examination
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- Replacing the blueprints
of the past
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Architecture​​ − Construction plans, exterior sketches - replacing the blueprints and
hand drawings of the past
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Training​​ − Flight simulators, computer aided instruction, etc
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Simulation and modeling​​ − Replacing physical modeling and enactments

5
...
The design of geometric models for object shapes, in particular, is often
called computer-aided geometric design (CAGD)
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CAD is also widely used
to produce computer animation for special effects in movies, advertising, technical
manuals
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CAD is mainly used for design of buildings,
automobiles,aircraft,water craft, spacecraft, computer, textiles and many other products
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Presentation graphics is commonly used to summarize financial, statically, mathematical,
Scientific and economic data for research reports, managerial reports
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Computer Art
Computer graphics method are widely used in both fine art & commercial art application
...
A paint brush program that allows artists to paint pictures on the screen of a
video monitor
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Entertainment
Computer graphics methods are now commonly used in making picture, music video &
television shows
...
Music videos
use graphics in several ways
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Computer simulations have become a useful part of mathematical modeling of many natural
systems in physics (computational physics), chemistry and biology, human systems in
economics, psychology, and social science and in the process of engineering new
technology, to gain insight into the operation of those systems, or to observe their behavior
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ex:Training of ship
captains,aircraft,pilots,heavy equipment operations air traffic control personnel
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In contrast with scientific
visualization, information visualization focuses on abstract data sets, such as unstructured
text or points in high-dimensional space, that do not have an inherent 2D or 3D geometrical
structure
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The emphasis is on realistic rendering of volumes, surfaces, illumination sources, and so
forth, perhaps with a dynamic (time) component
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Image Processing
In computer graphics a computer is used to create a picture, Image processing applies
techniques to modify or interpret existing pictures such as photographs and Tv scans
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To apply image processing method we first digitize a photograph or
other picture into an image file
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Medical application also make extensive use of image processing techniques for
picture enhancement in tomography and in simulation of operations
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A major components
of a graphical interface is a window manager that allows a user to display multiple windows
areas
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Cathode Ray Tube
The primary output device in a graphical system is the video monitor
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Basic Operation of a CRT
The basic operation of CRT is shown in figure below:

Electron Gun
The primary components of an electron gun in a CRT are the heated metal cathode and a
control grid
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This causes electrons to be boiled off the hot cathode surface
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The accelerating voltage can be generated with a
positively charged metal coating on the in side of the CRT envelope near the phosphor
screen, or an accelerating anode can be used
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Focusing System

The focusing system is used to create a clear picture by focusing the electrons into a narrow
beam
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Focusing is acomplished with either electric or magnetic fields
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In case of magnetic field, two pairs of coils are used, one for horizontal deflection
and other for vertical deflection
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CRT Screen
The inside of the large end of a CRT is coated with a fluorescent material that gives off
light when struck by electrons
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Then a
part of beam energy is converted into heat energy and the remainder part causes the
electrons in the phospor atom to move up to higher energy levels
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During this period, we see a glowing
spot that quickly fades after all excited electrons are returned to their ground state
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Persistence is defined as the time it take the emitted light from the screen to decay to
one-tenth of its original intensity
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A phosphor with low persistence is useful for
animation ; a high-persistence phosphor is useful for displaying highly complex, static
pictures
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Resolution
The number of points per centimeter that can be used be plotted horizontlly and
vertically
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The resolution of a CRT is depend on
•
•
•

type of phosphor
intensity to be displayed
focusing and deflection system

Aspect Ratio
It is ratio of horozontal to vertical points
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Raster Scan
In a raster scan system, the electron beam is swept across the screen, one row at a time from
top to bottom
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Picture definition is stored in memory area called the ​Refresh Buffer​​ or ​Frame Buffer​​
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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
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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
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•
•

low resolution
expensive

Disadvantages

•

electron beam directed to whole screen

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
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Picture definition is stored as a set of line-drawing commands in an area of memory referred
to as the ​refresh display file​​
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After all the
line-drawing commands are processed, the system cycles back to the first line command in
the list
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A line connects two points
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To draw a line, you need two
points between which you can draw a line
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Advantages
•
•

Produced smooth line drawings
High resolution

Disadvantages
•
•

Designed only for line drawing applications
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Color CRT Monitors
A color CRT monitor displays color picture by using a combination of phosphors that emit
different colored light
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Two basic methods for producing color displays are:
Beam Penetration Method
Random scan monitors use the beam penetration method for displaying color picture
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A beam of
slow electrons excites ony the outer red layer, while a beam of fast electrons penetrates red
layer and excites the inner green layer
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Advantages
•

Less expensive

Disadvantages
•
•

Quality of images are not good as comparatable with other methods
Four colors are allowed only

Shadow Mask Method
Raster scan system are use shadow mask methods to produced a much more range of colors
than beam penetration method
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One phosphor dot
emits a red light, second emits a green light and third emits a blue light
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Disadvantages
•
•
•

low resolution
expensive
electron beam directed to whole screen

•

Full Color System
Color CRTs in graphics systems are designed as RGB monitors
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A RGB color system with
34 bits of storage per pixel is known as full color system or true color system
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The term “flat-panel
display” is actually a misnomer, since thinness is the distinguishing characteristic
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Cathode-ray
tubes cannot be thin because the light is generated by the process of cathodoluminescence
whereby a high-energy electron beam is scanned across a screen covered with an inorganic
phosphor
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For a flat-panel display technology to be successful, it must at least match the basic
performance of a cathode-ray tube by having (1) full color, (2) full gray scale, (3) high
efficiency and brightness, (4) the ability to display full-motion video, (5) wide viewing angle,
and (6) wide range of operating conditions
...
These four attributes are not possible in a
cathode-ray tube
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Unenergized, the crystals direct light through
two polarizing filters, allowing a natural background color to show
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The more the molecules are twisted, the better the contrast and
viewing angle
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LCDs were
then widely used for a myriad of monochrome displays and still are
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3
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Basic input devices include the
● Keyboard
● Mouse
● Digitizer
● Trackball
● Touch Screens
● Light Pens
● Microphones
● Bar code readers
● Joysticks
● Scanners
● Voice Systems

Keyboard
The keyboard is the most common input device for entering numeric and alphabetic data in
to a computer system by pressing a set of keys which are mounted on the keyboard, which is
connected to computer system
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● Punctuation Keys - comma, period, semicolon, and so on
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● Application:Used to enter Text string,Short cuts to many function
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Mouse
● A mouse is a small device that a computer user pushes across a desk surface in order
to point to a place on a display screen and to select one or more actions to take from
that position
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● Hand held box used to position the screen cursor
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Generally there are 2 or 3 buttons used for operations like recording of the
cursor positions or invoking of a function
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The z-mouse is an example of this
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These tablets may also be used to capture data
or handwritten signatures
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The image generally does not appear on the tablet itself but, rather, is
displayed on the computer monitor
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● Some tablets are intended as a general replacement for a mouse as the primary
pointing and navigation device for desktop computers
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The tip of the light pen contains a light-sensitive element which, when placed
against the screen, detects the light from the screen enabling the computer to
identify the location of the pen on the screen
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Touch Screen
● A touchscreen is a display which can detect the presence and location of a touch
within the display area
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Touchscreens can also sense other passive objects,
such as a stylus
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The ability to interact directly with a display
typically indicates the presence of a touchscreen
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First, it enables one to interact with what is
displayed directly on the screen, where it is displayed, rather than indirectly with a
mouse or touchpad
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Such displays can be
attached to computers or, as terminals, to networks
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Image Scanners
● A scanner is a device that optically scans images, printed text, handwriting, or an
object, and converts it to a digital image
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Hand-held scanners, where the device is moved by hand, have
evolved from text scanning "wands" to 3D scanners used for industrial design,
reverse engineering, test and measurement, orthotics, gaming and other applications
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● Modern scanners typically use a charge-coupled device (CCD) or a Contact Image
Sensor (CIS) as the image sensor, whereas older drum scanners use a photomultiplier
tube as the image sensor
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Other
types of scanners are planetary scanners, which take photographs of books and
documents, and 3D scanners, for producing three-dimensional models of objects
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Due to increasing resolution and new features
such as anti-shake, digital cameras have become an attractive alternative to regular
scanners
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Such equipment involves the use of speech
recognition processes, and can replace or supplement other input devices
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● Speech recognition (also known as automatic speech recognition or computer speech
recognition) converts spoken words to machine-readable input (for example, to key
presses, using the binary code for a string of character codes)
...
Confusingly, journalists and
manufacturers of devices that use speech recognition for control commonly use the
term Voice Recognition when they mean Speech Recognition
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Joysticks are often used to
control video games, and usually have one or more push-buttons whose state can
also be read by the computer
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● The joystick has been the principal flight control in the cockpit of many aircraft,
particularly military fast jets, where centre stick or side-stick location may be
employed
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Miniature

finger-operated joysticks have been adopted as input devices for smaller electronic
equipment such as mobile phone
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The user rolls the ball with the thumb, fingers, or the
palm of the hand to move a cursor
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Before the advent of the touchpad, small trackballs
were common on portable computers, where there may be no desk space on which to
run a mouse
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The trackball was invented
by Tom Cranston and Fred Longstaff as part of the Royal Canadian Navy's DATAR
system in 1952, eleven years before the mouse was invented
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● When mice still used a mechanical design (with slotted 'chopper' wheels interrupting
a beam of light to measure rotation), trackballs had the advantage of being in contact
with the user's hand, which is generally cleaner than the desk or mousepad and
doesn't drag lint into the chopper wheels
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Most trackballs
now have direct optical tracking which follows dots on the ball
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Some have a scroll wheel like most mice, but the most
common type is a “scroll ring” which is spun around the ball
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4
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Basic output devices include the

•
•
•

Monitors
Printers
Plotters

Output Device - Printer
Printers are the most commonly used output devices for producing hard copy output
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Unlike a regular printer, the
plotter can draw continuous point-to-point lines directly from vector graphics files or
commands
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Plotters were the first type of printer that could print with
color and render graphics and full-size engineering drawings
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They are most frequently used for CAE
(computer-aided engineering) applications, such as CAD (computer-aided design)
and CAM (computer-aided manufacturing)
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Apen moves along the arm
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Acombination of the two thus provides movement along the
horizontal and vertical axes
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This is called a flat-bed plotter
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The drum rotates while the pen
moves laterally along a fixed rail
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● To draw clear and high-qualit diagrams, a plotter needs high-quality pens with special
inks of different colors
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A plotter is more software-dependent than any other peripheral, and needs much more
instructions than printer for producing output
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Many of the plotters now available in the market are desktop models that can
be used with PCs
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) as well as for engineering drawings
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These
computer graphics may be clip art,web graphics,logos,headings,backgrounds,digital photos or
other kind of digital images
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Types:(1)Programming package(2)Application package

DDA Algorithm
Digital Differential Analyzer (DDA) algorithm is the simple line generation algorithm which
is explained step by step here
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Step 2​​ − Calculate the difference between two end points
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If dx > dy, then you need more steps in x coordinate; otherwise in y
coordinate
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Xincrement = dx / (float) steps;
Yincrement = dy / (float) steps;
Step 5​​ − Put the pixel by successfully incrementing x and y coordinates accordingly and
complete the drawing of the line
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The big
advantage of this algorithm is that, it uses only integer calculations
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For example, as shown in the following illustration, from position (2, 3) you need to choose
between (3, 3) and (3, 4)
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At sample position Xk+1,Xk+1, the vertical separations from the mathematical line are
labelled as dupperdupper and dlowerdlower
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This simple decision is based on the difference between the two pixel positions
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dx(dlower−dupper)=dx(2dydx(xk+1)−2yk+2b−1)dx(dlower−dupper)=dx(2dydx(xk+1)−2yk+
2b−1)
=2dy
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yk+2dy+2dx(2b−1)=2dy
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yk+2dy+2dx(2b−1)
=2dy
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yk+C=2dy
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yk+C
So, a decision parameter PkPk for the ​k​th step along a line is given by −
pk=dx(dlower−dupper)pk=dx(dlower−dupper)
=2dy
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yk+C=2dy
...
yk+C
The
sign
of
the
decision
parameter PkPk is
the
same
as
of dlower−dupperdlower−dupper
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that

Remember, the coordinate changes occur along the x axis in unit steps, so you can do
everything with integer calculations
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xk+1−2dx
...
xk+1−2dx
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So −
pk+1=pk+2dy−2dx(yk+1−yk)pk+1=pk+2dy−2dx(yk+1−yk)
Where, Yk+1–YkYk+1–Yk is either 0 or 1 depending on the sign of PkPk
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Step 2​​ − Plot the point (x0,y0)(x0,y0)
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For m > 1, find out whether you need to increment x while incrementing y each time
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Mid-Point Algorithm
Mid-point algorithm is due to Bresenham which was modified by Pitteway and Van Aken
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Now you need to decide whether to put the next point at E or N
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If the intersection point Q is
closest to the point N then N is considered as the next point; otherwise E
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If the intersection point Q of
the line with the vertical line connecting E and N is below M, then take E as the next point;
otherwise take N as the next point
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There are two popular
algorithms for generating a circle − ​Bresenham’s Algorithm​​ and ​Midpoint Circle
Algorithm​​
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Let us discuss the algorithms in detail −
The equation of circle is X2+Y2=r2,X2+Y2=r2, where r is radius
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Instead, we have to choose the
nearest pixel position to complete the arc
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This can be decided by the decision parameter ​d​
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●

If d > 0, then S(X+1, Y-1) is to be chosen as the next pixel
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Set P=0 and Q=R
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Step 3​​ − Repeat through step-8 while X < Y
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Step 5​​ − Increment the value of P
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Step 7​​ − Else Set Y = Y + 1, D = D + 4(X-Y) + 10
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Draw Circle Method(X, Y, P, Q)
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Call Putpixel (X - P, Y + Q)
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Call Putpixel (X - P, Y - Q)
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Call Putpixel (X - Q, Y + X)
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Call Putpixel (X - Q, Y - X)
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)
f​(​x​,​ y​)​ ​=​ x​2​ ​+​ y​2​ ​-​ r​2​ ​=​ ​0
f​(​x​i​ ​-​ ​1​/​2​ ​+​ e​,​ y​i​ ​+​ ​1​)
​=​ ​(​x​i​ ​-​ ​1​/​2​ ​+​ e​)2​​ ​+​ ​(​y​i​ ​+​ ​1​)2​​ ​-​ r​2

​=​ ​(​x​i​-​ ​1​/​2​)2​​ ​+​ ​(​y​i​ ​+​ ​1​)2​​ ​-​ r​2​ ​+​ ​2​(​x​i​ ​-​ ​1​/​2​)​e ​+​ e​2
​=​ f​(​x​i​ ​-​ ​1​/​2​,​ y​i​ ​+​ ​1​)​ ​+​ ​2​(​x​i​ ​-​ ​1​/​2​)​e ​+​ e​2​ ​=​ ​0

Let​ d​i​ ​=​ f​(​x​i​ ​-​ ​1​/​2​,​ y​i​ ​+​ ​1​)​ ​=​ ​-​2​(​x​i​ ​-​ ​1​/​2​)​e ​-​ e​2
Thus​,

If​ e ​<​ ​0​ ​then​ di ​>​ ​0​ so choose point S ​=​ ​(​x​i​ ​-​ ​1​,​ y​i​ ​+​ ​1​)
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Step 4​​ − Determine the symmetry points in other seven octants
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X = X + X​C​, Y = Y + Y​C
Step 6​​ − Repeat step-3 through 5 until X >= Y

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