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Unit-01-Introduction to Computer Graphics
1.1 Introduction
1.2 Image Processing as Picture Analysis
1.3 The advantages of Interactive Graphics
1.4 Representative ses of !omputer Graphics
1." !lassification of Applications
1.# $evelopment of %ard&are and 'oft&are for !omputer Graphics
1.#.1 (utput Technology
1.#.1.1 Architecture of a )ector $isplay
1.#.1.2 Architecture of a Raster $isplay
1.#.1.3 $irect*vie& storage tu+es
1.#.2 Input Technology
1.#.3 'oft&are Technology
1., !onceptual -rame&or for Interactive Graphics
. %istory
1/#30 'utherland -irst Graphics orstation 1/#/0 -irst 'IGGRAP% A!
5arly 1/,67s0 Raster Graphics8 'hading8 Illumination
9ate 1/,67s0 Te:ture apping8 Ray Tracing
5arly 1/;67s0 Realism in Rendering
9ate 1/;67s0 Physically
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he computer is an information processing machine. It is a tool for storing8 manipulating and
correlating data. There are many &ays to communicate the processed information to the
user.
The computer graphics is one of the most effective and commonly used &ays to
communicate the processed information to the user. It displays the information in the form
of graphics o+>ects such as pictures8 charts8 graphs and diagrams instead of simple te:t.
Thus &e can say that computer graphics maes it possi+le to e:press data in pictorial form.
In computer graphics8 pictures or graphics o+>ects are presented as a collection of discrete
picture elements called pi:els. The pi:el is the smallest addressa+le screen element. It is the
smallest piece of the display screen &hich &e can control. The control is achieved +y
setting the intensity and color of the pi:el &hich compose the screen.
5ach pi:el on the graphics display does not represent mathematical point. Rather8 it
represents a region &hich theoretically can contain an infinite num+er of points. -or
e:ample8 if &e &ant to display point P1 &hose coordinates are 4.28 3.; and point P2
&hose coordinates are 4.;8 3.1 then P1 and P2 are represented +y only pi:el 4838 as
sho&n in the -ig. 1.1. In general8 a point is represented +y the integer part of : and integer
part of y8 i.e.8 pi:el int :8 int y.
Fig. 1.1: Pixel display area of 6 x 5
The special procedures determine &hich pi:el &ill provide the +est appro:imation to the
desired picture or graphics o+>ect. The process of determining the appropriate pi:els for
representing picture or graphics o+>ect is no&n as rasterization, and the process of
representing continuous picture or graphics o+>ect as a collection of discrete pi:els is called
scan conversion.
The computer graphics allo&s rotation8 translation8 scaling and performing various
pro>ection on the picture +efore displaying it. It also allo&s to add effects such as hidden
surface removal8 shading or transparency to the picture +efore final representation.
It provides user the control to modify contents8 structure8 and appearance of pictures or
graphics o+>ects using input devices such as a ey+oard8 mouse8 or touch*sensitive panel on
the screen.
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There is a close relationship +et&een the input devices and display devices. Therefore8
graphics devices includes +oth input devices and display devices.
1.2 Image Processing as Picture Analsis
The computer graphics is a collection8 contri+ution and representation of real or imaginary
o+>ects from their computer*+ased models. Thus &e can say that computer graphicsconcerns the pictorial synthesis of real or imaginary o+>ects.
%o&ever8 the related field image processing or sometimes called picture analysis concerns
the analysis of scenes8 or the reconstruction of models of 2$ or 3$ o+>ects from their
picture. This is e:actly the reverse process.
The image processing can +e classified as
o Image enhancement
The image enhancement deals &ith the improvement in the image ?uality
+y eliminating noise or +y increasing image contrast.
o Pattern detection and recognition
Pattern detection and recognition deal &ith the detection and clarification of
standard patterns and finding deviations from these patterns. The optical
character recognition (!R technology is an practical e:ample of pattern
detection and recognition.
o
'cene analysis and computer vision
'cene analysis and computer vision deals &ith the recognition and
construction of 3$ model of scene from several 2 $ images.
The a+ove three fields of image processing proved their importance in many area such as
finger print detection and recognition8 modeling of +uilding8 ships8 automo+iles etc. 8 and
so on.
The t&o field7s computer graphics and image processing of computer processing of picture.
In the initial stages they &ere ?uite separate disciplines.
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'econd image processing8 simple image processing operations are often used in computer
graphics to help synthesi=e the image of a model.
1.! "he advantages o# Interactive Graphics
9et us discuss the advantages of interactive graphics.
Today8 a high ?uality graphics display of personal computer provide one of the most
natural means of communication &ith a computer.
It provides tools for producing pictures not only of concrete8 @real*&orld o+>ects +ut also
of a+stract8 synthetic o+>ects8 such as mathematical surfaces in 4$ and of data that have no
inherent geometry8 such as survey results.
It has an a+ility to sho& moving pictures8 and thus it is possi+le to produce animations &ith
interactive graphics.
ith interactive graphics use can also control the animation +y ad>usting the speed8 the
portion of the total scene in vie&8 the geometric relationship of the o+>ects in the scene to
one another8 the amount of detail sho&n and so on.
The interactive graphics provides tool called motion dnamics. ith this tools user can
move and tum+le o+>ects &ith respect to a stationary o+server8 or he can mae o+>ects
stationary and the vie&er moving around them. A typical e:ample is &al throughs made
+y +uilder to sho& flat interior and +uilding surroundings. In many case it is also possi+le
to move +oth o+>ects and vie&er.
The interactive graphics also provides facility called update dnamics. ith update
dynamics it is possi+le to change the shape8 colour or other properties of the o+>ects +eing
vie&ed.
ith the recent development of digital signal processing $'P and audio synthesis chip
the interactive graphics can no& provide audio feed+ac along &ith the graphical
feed+acs to mae the simulated environment even more realistic.
In short8 interactive graphics permits e:tensive8 high*+and&idth user*computer interaction.
It significantly enhances the a+ility to understand information8 to perceive trends and to
visuali=e real or imaginary o+>ects either moving or stationary in a realistic environment. It
also maes it possi+le to get high ?uality and more precise results and products &ith lo&er
analysis and design cost.
1.$ %epresentative Uses o# Computer Graphics
The use of computer graphics is &ide spread. It is used in various areas such as industry8 +usiness8
government organi=ations8 education8 and entertainment. 9et us discuss the representative uses of
computer graphics in +rief.
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User Inter#aces& ser friendliness is one of the main factors underlying the success and
popularity of any system. It is no& &ell esta+lished fact that graphical interfaces provide
and attractive and easy interaction +et&een users and computers. The +uilt*in graphics
provided &ith user interfaces use visual control items such as +uttons8 menus8 icons8 scroll
+ar etc8 &hich allo&s user to interact &ith computer only +y mouse*clic. Typing is
necessary only to input te:t to +e stored and manipulated.
Plotting o# graphics and chart& In industry8 +usiness8 government and educational
organi=ations8 computer graphics is most commonly used to create 2$ and 3$ graphs of
mathematical8 physical and economic functions in form of histograms8 +ars and pie*charts.
These graphs and charts are very useful for decision maing.
'##ice automation and (es)top Pu*lishing& The destop pu+lishing on personal
computers allo& the use of graphics for the creation and dissemination of information.
any organi=ations does the in*house creation and printing of documents. The destop
pu+lishing allo&s user to create documents &hich contains te:t8 ta+les8 graphs and other
forms of dra&n or scanned images or pictures. This is one approach to&ards the office
automation.
Computer-aided (ra#ting and (esign& The computer*aided drafting uses graphics to
design components and systems electrical8 mechanical8 electromechanical and electronic
devices such as automo+ile +odies8 structures of +uilding8 airplane8 ships8 very large*scale
integrated )9'I chips8 optical systems and computer net&ors.
+imulation and Animation0 se of graphics in simulation maes mathematical models
and mechanical systems more realistic and easy to study. The interactive graphics
supported +y animation soft&are proved their use in production of animated movies and
cartoons films.
Art and Commerce& There is a lot of development in the tools provided +y computer
graphics. This allo&s user to create artistic pictures &hich e:press messages and attract
attentions. 'uch pictures are very useful in advertising.
Process Control& ect to +e dra&n0 2$ or 3$. It can also +e classified according
to ind of picture0 'ym+olic or Realistic. any computer graphics applications are classified +y
the type of interaction. The type of interaction determines the user7s degree of control over the
o+>ect and its image. In controlla+le interaction user can change the attri+utes of the images. Role
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of picture gives the another classification. !omputer graphics is either used for representation or it
can +e an end product such as dra&ings. Pictorial representation gives the final classification to use
computer graphics. It classifies the use of computer graphics to represent pictures such as line
dra&ing8 +lac and &hite8 colour and so on.
-ig. 1.2
1. (evelopment o# ard/are and +o#t/are #or Computer Graphics
The development of hard&are of computer graphics involves the development of input and output
device technology. Therefore8 in all development of computer graphics involves the development
in three fields0
1. (utput technology
2. Input technology and
3. 'oft&are technology
1..1 'utput "echnolog
-ig. 1.3 sho&s the historical development in the output technology. In early days of computer the
hardcopy devices such as teletype printer and line printer &ere in use &ith computer driven !RT
displays. In mid fifties command and control !RT display consoles &ere introduced. The more
display devices developed in mid*si:ties and in common use until the mid*eighties8 are called
vector8 stroe8 line dra&ing or calligraphic displays. The term vector is used as a synonyms for
lineB a stroe is a short line8 and characters are made of se?uence of such stroes.
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-ig. 1.3
1..1.1 Architecture o# a ector (ispla
-ig. 1.40 )ector 'can !RT
As sho&n in -ig. 1.4 vector scan !RT display directly traces out only the desired lines on !RT i.e
If &e &ant a line connection point A &ith point < on the vector graphics display. e simply drive
the +eam deflection circuitry &hich &ill cause +eam to go directly from point A to
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-ig. 1."0 Architecture of a vector display
In vector displays +eam is deflected from end point to end point8 hence this techni?ue is also calledrandom scan. e no& as +eam8 stries phosphor it emits light.
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ig. 1.& %aster +can C%"
In this method8 the hori=ontal and vertical deflection signals are generated to move the +eam all
over the screen in a pattern sho&n in the -ig. 1.,.
%ere8 the +eam is s&ept +ac forth from left to right across the screen. hen the +eam is moved
from the left to right8 it is (D. The +eam (--8 &hen it is moved from right to left as sho&n +ydotted line in -ig. 1.,
hen the +eam reaches the +ottom of the screen8 it is made (-- and rapidly retraced +ac to the
top to start again. A display produced in this &ay is called raster scan display. Raster scanning
process is similar to reading different lines on the page of a +oo. After completion of scanning of
one line8 the electron +eam files +ac to the start of ne:t line and process repeats. In the raster scan
display8 the screen images is maintained +y repeating scanning the same image. This process is
no&n as re#reshing o# screen.
ector +can (ispla %aster +can (ispla
1. In vector scan display the +eam is
moved +et&een the end points of the
graphics primitives
1. In raster scan display the +eam is moved all
over the screen one scan line at a time8 from top
to +ottom and then +ac to top.
2. )ector display flicers &hen the
num+er of primitives in the +uffer
+ecomes too large.
2. In raster display8 the refresh process is
independent of the comple:ity of the image.
3. 'can conversion is not re?uired. 3. Graphics primitives are specified in terms of
their endpoints and must +e scan converted into
their corresponding pi:els in the frame +uffer.
4. 'can conversion hard&are is not
re?uired.
4.
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". )ector display dra&s a continuous
and smooth lines
". Raster display can display mathematically
smooth line8 polygons and +oundaries of
curved primitives only +y appro:imating them
&ith pi:els on the raster grid.
#. !ost is more. #. !ost is lo&.
,. )ector display only dra&s lines
and characters.
,. Raster display has a+ility to display areas
filled &ith solid colors or patterns.
1..1.! (irect-vie/ storage tu*es
In last si:ties8 the direct*vie& storage tu+e $)'T &as introduced in the display technology. The
direct*vie& storage tu+es $)'T give the alternative method of maintaining the screen image. A
$)'T uses the storage grid &hich stores the picture information as a charge distri+ution >ust
+ehind the phosphor*coated screen.
The -ig. 1.; sho&s the general arrangement of the $)'T. It consists of t&o electron guns0 a
primary gun and a flood gun.
ig. 1.3& Arrangement o# (+"
A primary gun stores the picture pattern and the flood gun maintains the picture display. A primary
gun produces high speed electrons &hich strie on the storage grid to dra& the picture pattern. As
electron +eam stries on the storage grid &ith high speed8 it nocs out electrons from the storage
grid eeping the positive charge. The noced out electrons are attracted to&ards the collector. The
net positive charges on the storage grid is nothing +ut the picture pattern. The continuous lo&
speed electrons from flood gun pass through the control grid and are attracted to the positive
charged areas of the storage grid. The lo& speed electrons then penetrate the storage grid and strie
the phosphor coating &ithout affecting the positive charge pattern on the storage grid. $uring thisprocess the collector >ust +ehind the storage grid smooth out the flo& of flood electrons.
Advantages o# (+"
1. Refreshing of !RT is not re?uired.
2.
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(isadvantages o# (+"
1. They do not display colors and are availa+le &ith single level of line intensity.
2. 5rasing re?uires removal of change on the storage grid. Thus erasing and redra&ing process
taes several seconds.
3. 'elective or part erasing of screen is not possi+le.
4. 5rasing of screen produces unpleasant flash over the entire screen surface &hich prevents its use
of dynamic graphics applications.
". It has poor contrast as a result of the comparatively lo& accelerating potential applied to the
flood electrons.
#. The performance of $)'T is some &hat inferior to the refresh !RT.
In early seventies the ine:pensive raster graphics displays &ere developed. Raster displays store
the display primitives such as lines8 characters solid and filled patterns in a refresh +uffer in
terms of their corresponding pi:els.
1..2 Input "echnolog
Input technology has also improved greatly over the years. Dum+er of input devices &ere
developed over the years. These devices are punch cards8 light pens8 ey+oard8 ta+les8 mouse and
scanners.
1..! +o#t/are "echnolog
9ie output and input technology there is a lot of development in the soft&are technology.
In early days lo& level soft&are &ere availa+le. (ver the years soft&are technology moved
from lo& level to device dependent and then to device independent pacages.
The device independent pacages are high level pacages &ith can drive a &ide variety of
display and printer devices. As a need for the device independent pacage standardi=ation
is made and specifications are decided.
The first graphics specification to +e officially standardi=ed &as GE' the Graphical
Eernel 'ystem. GE' supports the grouping of logically related primitives such as lines8
polygons8 and character strings and their attri+utes in collected form called segments.
In 1/;;8 a 3$ e:tension of GE'8 +ecame an official standard8 as did a much more
sophisticated +ut even more comple: graphics system called P%IG' Programmer7s
%ierarchical Interactive Graphics 'ystem.
P%IG'8 as its name implies8 supports nested hierarchical grouping of 3$ primitives8 called
structures.
In P%IG'8 all primitives are su+>ected to geometric transformations such as scaling8
rotation and translation to accomplish dynamic movement. P%IG' also supports a data+ase
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of structures the programmer may edit and modify. P%IG' automatically updates the
display &henever the data+ase has +een modified.
1. Conceptual rame/or) #or Interactive Graphics
The -ig. 1./ sho&s the high level conceptual frame&or for interactive graphics. It consists of
input and output devices8 graphics system8 application program and application model. A computer
receives input from input devices8 and outputs images to a display device. The input and output
devices are called the hard&are components of the conceptual frame&or. There are three soft&arecomponents of conceptual frame&or.
These are0
Application odel
Application Program and
Graphic 'ystem
ig. 1.4& Conceptual #rame /or) #or interactive graphics
Application 5odel& The application model captures all the data and o+>ects to +e pictured on the
screen. It also captures the relationship among the data and o+>ects. These relationships are stored
in the data+ase called application data+ase8 and referred +y the application programs.
Application program& It creates the application model and communicates &ith it to receive and
store the data and information of o+>ect7s attri+utes. The application program also handles user
input. It produces vie&s +y sending series of graphics output commands to the graphics system.
The application program is also responsi+le for interaction handling. It does this +y event handling
loops.
Graphics +stem& It accepts the series of graphics output commands from application program.
The output commands contain +oth a detailed geometric description of &hat is to +e vie&ed and
the attri+utes descri+ing ho& the o+>ects should appear. The graphics system is responsi+le for
actually producing the picture from the detailed descriptions and for passing the user7s input to the
application program for processing.
1.3 +ummar
!omputer graphics is one of the most e:citing and rapidly gro&ing computer field. It is also an
e:tremely effective medium for communication +et&een human +eings and computers. It is one of
the most effective and commonly used &ay to communicate the processed information to the user.
ainly this unit deals &ith the image processing as picture analysis8 advantages of interactive
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graphics8 representative uses of computers graphics. !lassification of applications and
development of hard&are and soft&are for computer graphics.
1.4 "erminal 6uestions
1. $iscuss on topic image processing as picture analysis.
2. 9ist the advantages of interactive graphics.
3. 5:plain the representative uses of computer graphics.
4. 5:plain the classification of use of computer graphics.
". 5:plain the development of hard&are and soft&are for computer graphics.
#. 5:plain the architecture of a vector display.
,. 5:plain the architecture of a raster display.
;. Give the comparison +et&een vector scan display and raster scan display.
/. Give historical development of output technology.
16. rite a short note on
a. Input technology
+. + 'oft&are technology
11. ith a neat +loc diagram e:plain the conceptual frame&or of interactive graphics.