Introduction to Computer Graphics

UNIT 1 : INTRODUCTION TO
COMPUTER GRAPHICS
Prepared By
Prof. Sadia Patka
Assistant Professor
Anjuman College of Engineering and Technology
Department of Computer Science & Engineering
Fifth Semester
Subject: COMPUTER GRAPHICS

OVERVIEW OF
COMPUTER GRAPHICS (CG)

Definition and Importance of Computer Graphics
• The term computer graphics (CG) describes the use of
computers to create and manipulate images.
• Graphics can be two- or three-dimensional
• Computer Graphics is the creation and manipulation of images
or pictures with the help of computers.
• There are two types of computer graphics :
1) Passive Computer Graphics (Non-interactive Computer
Graphics)
2) Active Computer Graphics (Interactive Computer Graphics)

Contd..
• The major product of computer graphics is a picture. With
the help of CG, pictures can be represented in 2D and 3D
space.
• Many applications show various parts of the displayed
picture changing in size and orientation. Such type of
transformations i.e. the pictures can be made to grow,
shrink, rotate and etc. can be achieved through CG.
• The display on them is often too big to be shown in their
entirety. Thus, with the help of CG, a technique called
clipping can be used to select just those parts of the
picture that lie on the screen and to discard the rest.

• CG is in daily use in the field of science, engineering,
medicine, entertainment, advertising, the graphic arts, the
fine arts, business, education etc.
• The electronic industry is more dependent on the
technologies provided by CG such as engineers can draw
their circuit in a much shorter time,
• architects can have alternative solution to design
problems,
• the molecular biologist can display pictures of molecules
and can study on the structure,
• the town planners and transportation engineers use the
computer generated maps which display data useful to
them in their planning work etc.
Contd..

Interactive Computer Graphics
• The Interactive computer graphics (ICG) provides two way
communications between the computer and the user.
• The various applications of ICG are as follows.
• Using ICG system the integrated electronic circuits which are
very complex can be drawn in a much shorter time.
• It is very useful in training of the pilots as they spend much of
their training on the ground at the controls of a flight simulator
and not in a real aircraft.
• There are many tasks that can be made easier & less expensive
by the use of ICG. The effectiveness of the ICG is the speed
with which the user can absorb the displayed information.

Contd..
• The Interactive Graphics display consists of three major
components as follows & shown in Figure 1:
(1) Frame Buffer (2) T.V. Monitor (3)Display Controller
10001101
01101010
00101001
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00111001
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Display Adapter/
Display Controller
Frame Buffer
Video Monitor/
T. V. Monitor
Scan line Data

Contd..
1) Frame Buffer
• The images that are to be displayed are stored in a frame buffer in the form of matrix
of intensity values.
• The frame buffer contains the image stored in binary form as a matrix of 0’s and 1’s
which represent the pixel. 0 indicates the darkness and 1 indicates the image.
• The Frame Buffer holds the set of intensity values for all the screen points.
• The intensity values stored in a Frame Buffer are retrieved and painted on a screen
one row at a time. This row is called as scan line.
2) Display Controller
• The Display Controller passes the contents of frame buffer to the T.V. Monitor.
• Display Controller reads successive bytes of data from the frame buffer & then
converts 0’s and 1’s into the corresponding video signal.
• These signals are fed to the T.V. Monitor.
3) T.V. Monitor
• The T.V. Monitor then produces black and white pattern on the screen.
• The frame Buffer contents are to be modified, in order to represent the new pattern of
pixels or if some changes are to be made on the displayed picture.

GRAPHICS AREAS
The following major areas of computer graphics are:
• Modeling deals with the mathematical specification of
shape and appearance properties in a way that can be stored
on the computer. For example, a coffee mug might be
described as a set of ordered 3D points along with some
interpolation rule to connect the points and a reflection
model that describes how light interacts with the mug.
• Rendering is a term inherited from art and deals with the
creation of shaded images from 3D computer models.
• Animation is a technique to create an illusion of motion
through sequences of images. Animation uses modeling and
rendering but adds the key issue of movement over time,
which is not usually dealt with in basic modeling and
rendering.

Contd..
There are many other areas that involve computer graphics.
• User interaction deals with the interface between input devices
such as mice and tablets, the application, feedback to the user in
imagery, and other sensory feedback.
• Virtual reality attempts to immerse the user into a 3D virtual world.
This typically requires at least stereo graphics and response to head
motion. For true virtual reality, sound and force feedback should be
provided as well.
• Visualization attempts to give users insight into complex
information via visual display.
• Image processing deals with the manipulation of 2D images and is
used in both the fields of graphics and vision.
• 3D scanning uses range-finding technology to create measured 3D
models. Such models are useful for creating rich visual imagery, and
the processing of such models often requires graphics algorithms.
• Computational photography is the use of computer graphics,
computer vision, and image processing methods to enable new ways
of photographically capturing objects, scenes, and environments.

COMPUTER GRAPHICS APPLICATION
Almost any field can make some use of computer graphics, but the major
consumers of computer graphics technology include the following
industries:
• Video games increasingly use sophisticated 3D models and rendering
algorithms.
• Cartoons are often rendered directly from 3D models. Many traditional 2D
cartoons use backgrounds rendered from 3D models, which allows a
continuously moving viewpoint without huge amounts of artist time.
• Visual effects use almost all types of computer graphics technology.
Almost every modern film uses digital compositing to superimpose
backgrounds with separately filmed foregrounds. Many films also use 3D
modeling and animation to create synthetic environments, objects, and even
characters that most viewers will never suspect are not real.
• Animated films use many of the same techniques that are used for visual
effects, but without necessarily aiming for images that look real.
• CAD/CAM stands for computer-aided design and computer-aided
manufacturing. These fields use computer technology to design parts and
products on the computer and then, using these virtual designs, to guide the
manufacturing process. For example, many mechanical parts are designed
in a 3D computer modeling package and then automatically produced on a
computer-controlled milling device.

Contd..
• Simulation can be thought of as accurate video gaming. For example, a
flight simulator uses sophisticated 3D graphics to simulate the experience
of flying an airplane. Such simulations can be extremely useful for initial
training in safety-critical domains such as driving, and for scenario training
for experienced users such as specific fire-fighting situations that are too
costly or dangerous to create physically.
• Medical imaging creates meaningful images of scanned patient data. For
example, a computed tomography (CT) dataset is composed of a large 3D
rectangular array of density values. Computer graphics is used to create
shaded images that help doctors extract the most salient information from
such data.
• Information visualization creates images of data that do not necessarily
have a “natural” visual depiction. For example, the temporal trend of the
price of ten different stocks does not have an obvious visual depiction, but
clever graphing techniques can help humans see the patterns in such data.
• 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.

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 2 shown below
illustrates 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.

Contd..
Figure 2: A 3D graphic pipeline

Contd..
• 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.
1) The window to a viewport transformation. The
viewport is basically a sub – rectangle of a fixed
rectangle known as logical screen.
2) The transformation of logical screen coordinates to
physical device coordinates.

Contd..
Figure 3 (a): Sequence of transformation in viewing pipeline
Figure 3 (b): 2D coordinate system to physical device coordinates
transformation

Cathode Ray Tube (CRT)
• The most common graphics output device is the video
monitor which is based on the standard cathode ray tube
(CRT) design. Figure 4 illustrates the basic operation of a
CRT.
Figure 4: Cathode Ray Tube (CRT)

Contd..
• As shown in above figure, it consists of electron gun, focusing
system, deflection plates and a phosphor-coated screen.
• Electron gun is the primary component of a CRT. When the
heat is supplied to the electron gun by directing a current, a
beam of electrons emitted by an electron gun, passes through
focusing and deflection systems that direct the beam toward
specified positions on the phosphor-coated 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.
• There are two pairs of deflection plates - Horizontal
deflection plates and vertical deflection plates.
• One pair of plates is mounted horizontally to control the
vertical deflection, and the other pair is mounted vertically to
control horizontal deflection.

Contd..
• The beam passes between the two pairs of deflection plates
and positioned on the 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.
• In CRT monitors there are two techniques of displaying
images:
1) Raster scan displays
2) Random scan displays

Raster Scan Displays
Figure 5: Raster Scan Display Figure 6: Horizontal and Vertical
Retrace

Raster Scan Systems
Figure 7: Architecture of a simple raster system

Contd..
Figure 8: Architecture of a raster system

Raster Scan Display Processor
• Figure 9 shows one way to set up the organization of a raster system
containing a separate display processor, sometimes referred to as a
graphics controller or a display coprocessor.
Figure 9: Architecture of a raster-graphics system with a
display processor

Random Scan Display/ Vector-Scan
Display/ Calligraphic Displays
Figure 10: Random Scan Display

Random-Scan Systems/ Random-Scan Display
Processor
Figure 11: Architecture of a simple random scan system

HARD COPY DEVICES
• Printers
• Plotters
INPUT DEVICES FOR OPERATOR INTERACTION
• Keyboards
• Mouse
• Trackball and Spaceball
• Joysticks
• Data Glove
• Digitizers
• Touch Screens
• Light pen
• Voice Systems
• Image Scanners

Introduction to Computer Graphics

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