An ISO 9001:2008 Certified Organization PCTI Group Computer Graphics By : Pcti Group

An ISO 9001:2008 Certified Organization

PCTI Group

Computer Graphics

By : Pcti Group

© Copyright PCTI Group 2009Presentation Title | April 10, 2023 | <document classification>

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Session 1:

The Coverage:IntroductionConceptual FrameworkInteractive and PassiveGraphics.


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Computer Graphics

Computer Graphics is the Intermediary between the Application Model[program] and display HARDWARE that effects an output transformation from the objects In the application model to view of the model.


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Conceptual framework for Interactive Graphics:

GraphicsSystem

ApplicationModel

ApplicationProgram

Display Device/PC


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Interactive Graphics:

As per the framework, a computer receivesinput from interaction devices, and outputimages to a display device.The S/W has 3components:1.Application Program: It Creates,Stores,and retrieves from the third Component,which is Graphics System.2.Graphics System: This is responsible for actually producing the picture from the detaileddescriptions.3.Display Hardware: The actual HARDWARE device.


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Passive Graphics

A Computer Graphics Operation thattransforms automatically and Withoutoperator intervention.


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• User Interfaces • Interactive plotting in business,Science and Technology.

• Office automation and E-Publishing.• CAD and CAM application.• Simulation.• Art and Commerce.• Process Control.• Cartography.

Usage of Computer Graphics:


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Display Devices:•Refresh CRT.•Random and Raster Scan Monitor.•Color CRT Monitors.•Direct View Storage Tubes(DVST).•Flat Panel Displays.•Light Emitting Diodes and LCD’s.•Hard Copy Devices.


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The Coverage:

* Refresh CRT.* Deflection.

MAGNETIC

ELECTRONIC DEFLECTION

* Raster and Random ScanDisplays.

Session -2


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Cathode

Control Grid

Focussing Anode

AcceleratingAnode

DisplayScreen.

Electron Beam Path.

Refresh CRT:


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Base

Connector pins

Focussing System

HorizontalDeflectionPlates

Vertical DeflectionPlates

PhosphorScreen

ElectronBeam

Electrostatic deflection of the electron beam in a CRT.


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A Random scan system draws the Component lines of an object in any order Specified.

Random Scan System


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A Raster Scan system displays an Object as a set of discrete points Across each scan lines.

Raster Scan System


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In Some raster scan Systems(TV sets etc.) each frame is displayed into passes using an interlaced refresh procedure.In 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. Interlacing of the scan lines allows us to see the entire screen displayed in one half of the time and used with SLOWER REFRESHING RATES.

With Interlacing , each of the two passes can beaccomplished in 1/60th of a second.which brings the refresh rates nearer to 60 frames/second.This is the effecting Technique for avoiding flicker.

Interlacing


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Session 3:

The Coverage:

•Color CRT.•Shadow Masking.•DVST.•LED.•LCD.


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A CRT Monitors displays color pictures by using a combination of phosphorus that emit different colored light.By this , a range of different color displays with CRT arethe beam penetration method and shadow Masking.

ABeam penetration method has been used with a random scan monitors.Two layers of phosphor,red and green are coated onto the inside of the CRT SCREEN and the displayed Color depends on how far the electron beam penetrates into the phosphor layers.Its an inexpensive way to produce color in random scan monitors and qualities of pictures is not as Good as with other Methods.

Color CRT Monitors


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MagnifiedPhosphor-DoTriangle

screen

green

red

blue

Selection Of shadow Masking

Shadow Masking

Electron Guns


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An alternative method for maintaining a screen image is to store the picture the picture information inside the CRT instead of refreshing the screen. A direct View Storage Tube(DVST) stores the picture information as a charge distribution just behind the phosphor-coated screen.Two Electron guns are used in a DVST.One ,the primary gun, is used to store the picture pattern;the second,the flood gun,maintain the picture display. They Don’t display colors and that selected parts of a picture cannot be erased. To eliminate a picture,the entire screen must be erased and the modified picture redrawn. The erasing and redrawing process can take several seconds for a complex picture.

Direct -View Storage Tubes


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A third type of emissive device is the Light Emitting Diode.A matrix Of diode is arranged to form the pixel positions in the display, and the Picture definitions is stored in a refresh buffer.As in scan line refreshing of a CRT, information is read from the Refresh Buffer and converted to voltage levels that are applied to the diodes to Produce the light patterns in the display.

Light Emitting Diodes


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Commonly used in small systems ,such as calculators and computers.These non emissive devices produce a picture by Passing polarized light from the surroundings or from an Internal light source through a liquid crystal material that can Be aligned to either block or transmit signals (light).

Liquid Crystal Display


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Session 4:The Coverage:*Introduction of Scan conversion.*Scan about a point.*Scan about a line.


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IntroductionScan Converting About• a POINT.• a LINE.• a CIRCLE.• an ELLIPSE.Side effects of Scan Conversion

Scan Conversion


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Many scan conversion algorithms are implemented in computer hardware or firmware. However a specific graphic algorithm can be implemented in software. The most common used graphicsObjects are the line,the sector,arc,the ellipse,The rectangle and the polygon. * We will assume that all objects lie within the Boundaries of the display device coordinate system.

Introduction


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A mathematical point(x,y) where x and y are the real numbers within an image area, needs to be scan converted to a pixel at location(x’,y’)

Pixel grid

PixelCoordinates Pixel

Coordinates

PixelGrid

x

y

x

y

0.0 1.0 2.0 3.0

1.0

2.0

3.0

0 1 2 3

0

1

2

P1(1.7,0.8)

P2(2.2,1.3)

P3(2.8,1.9)

P1(1.7,0.8)

P2(2.2,1.3)

P3(2.8,1.9)

Scan Converting a point

Scan Converting Point


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A straight line may Be defined by two endpoints and an equation.The two End Points are described by(x1,y1) and (x2,y2).The equation of the line is used to describe the x,y coordinates of all the points that lie between these two endpoints.

x

y

Y

X

(X2,y2)

(X1,y1)

The Straight Line

Scan Converting a Scan Lines


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Session 5:

The Coverage:

*Introduction To Line Drawings:

BRESENHAM’SAlgorithm.

DDA Algorithm


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Bresenham's line algorithms is a highly efficient method for scan -converting lines.It produces mathematically accurate results using only integer addition,subtraction and multiplication by 2,which can be done by simple arithmetic shift operation.

x

y

Xi Xi+1

Yi

Yi+1

P1

t

s

T

S

Scan-ConvertedPoints

True Line

Bresenham's Line Algorithm


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DDA OR DIGITAL DIFFERENTIAL ANALYZER ALORITHM IS AN INCREMENTAL SCAN-CONVERSION METHOD.THIS APPROACH IS CHARACTERIZED BY PERFORMINGCALCULATIONS AT EACH STEP RESULTS FROM THE PRECEDING STEP.SUPPOSE at step I we have to calculated(Xi,Yi) to be point on the line.Since the next POINT on the line is (Xi+1,Yi+1) should satisfy delta y/delta x = m where delta Yi+1 –Yi and deltax = Xi+1 –Xi ,we have Yi+1 = Yi +m.delta XOR Xi+1 = Xi +delta/mThe DDA algorithm is faster than the direct use of line equation since it calculates Point the line with out any floating –point manipulation. However, a floating point addition still needed in determining each successive point.Furthermore, cumulative error due to limited precision in the floating point representation.May cause calculated points to draft away from their true position when the line is Relatively long.

DDA line Algorithm


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Session 6:

The Coverage:

*Scan Conversion of a Circle

*Defining a Circle.


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A Circle is the Symmetrical Figure. Any Circle Generating algo take advantage of the circle’s Symmetry to plot eight points for each value that the algorithm calculates. Eight way symmetry is used by reflecting each calculated points around each 45 degree axis.

x

y

1

23

4

5

6 7

8

12345

1 2 3 4

(X,Y)

(Y,X)(-Y,X)

(-X,Y)

(-x,-y)

(-y,-x) (y,-x)

(x,-y)

Scan Converting a Circle


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x

y

x

y

P=(Xir2

x2

rcosx

y r rcos

P=(r cos , r Sin

Circle defined with a second –egreePolynomial equation.

Circle defined with trigonometric functions

Defining a Circle


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Session: 7

The Coverage:*Scan Conversion of Ellipse.*Side Effects.


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The ellipse , like the circle,shows Symmetry.In the case of an ellipse,how ever,Symmetry is four rather than eight-way. There are two Methods of mathematically Defining an ellipse.

PLOYNOMIAL METHOD OF DEFINING AN ELLIPSE:

The polynomial method of defining an ellipse is given by the (X-h)

When the polynomial method is used to define an ellipse,the valueof x is added From h to a. For each step of x,each value of y is found by evaluating the expression.

Y = b

This method is very efficient,However, because the squares of a and (x-h) must be Found. Then floating point division of (x - h)

2

a

(Y-k)2

b= 1 Where (h,k) ellipse center

a= length of major axis.B= length of minor axis.

2 2

1 - + k

a 2

x - h2

By a And floating point

Multiplication of the square root [1 –(x-h)2 ] By b.

Scan -Converting an Ellipse


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1.ALIASING2.Overstrike

Side Effects of Scan Conversion


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Session: 8

The Coverage:•Transformations.•Transformation Types.•Geometric Transformation.


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Introduction:

The object of 2D Graphics Transformation is to describe there operations in mathematical form suitable for computer processing and how they are used to achieve the Ends of object manipulation and motion.

2D Graphics Transformation


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Transformation Types:

•Geometric Transformation

•Coordinate transformation

•Composite Transformation


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x

y

0

Object

0 x

y

p

p‘

Object

Under This ,An Object in the plane can be considered as set of points.Every object Point p has Coordinates (X,Y) and so the object is the sum total of all of its Coordinate points. If the object is moved to a new Position, it can be regarded as New Object Obj’, all of whose coordinate point P’ can be obtained from the original P by the application of a geometric transformation.

Geometric Transformation


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Session: 9

The Coverage:

*Coordinate Transformation.*Composite Transformation.* Concatenation of matrices.


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X

Y

X’

Y’

P(x,y)(x’,y’)

O

O’

Y

We have two coordinate Systems in the plane.The First System is located at the Origin O and has coordinate axes XY .The Second Coordinate System is located at origin O’ and has Coordinate axes x’y’ .Now each point in the Plane has two coordinate descriptions (x,y) and (x’,y’),depending upon which Coordinate System is used.IT MEANS THE TRANSFORMATION ARISING FROM A TRANSFORMATION APPLIED TO THE FIRST SYSTEM X,Y ,WE CAN SAY THAT A COORDINATE TRANSFORMATION HAS BEEN APPLIED.

Coordinate Transformation


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The More complex geometric and coordinate transformations can be built from the basic transformations by using the process of composition of functions.Here the basic transformation of rotation[displacement of objects Scaling and the reflection can be represented as matrix functions.

Geometric Transformations Coordinate Transformations

R = Cos -Sin

sincos

Cos Sin

sincos

-R

SSX. SY= S

X0

0 SY

SX. SY= S

X0

0 SY

1

1

Composite Transformation


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The advantage of introducing a matrix from for translation is that we can now build complex transformation by multiply the basic matrix transformations.This process is sometimes called concatenation of matrices.We must be able to represent the basic transformations as 3*3 homogeneous coordinate matrices so as to be compatible with the matrix of translation.

Concatenation Of Matrices


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Session: 10

The Coverage:

•Viewing and clipping.

•Window to view port Mapping.


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World coordinate System: Much Like what we see in real lifethrough a small window on the wall or the viewfinder or camera, a computer generated image often depicts a partial view of a large scene.Objects are placed into the scene by modeling transformations to a master coordinate Systemcalled as WORLD COORDINATE SYSTEM. A rectangular window withits edge parallel the axes of the WCS is used to select theportion of the scene for which an image is to be generated.

0 1

1

0World Coordinate System

Viewport

Workstation Window

WorkstationViewport

2D Viewing & Clipping


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Objective: The Objective of window -to -viewport mapping is to convert the world coordinates(wx,wy) of arbitrary point to its corresponding normalized device coordinates(vx,vy).

0

0

wy

wy

wx wx

vy

vy

vy vy1

WINDOW VIEWPORT

Window To View port Mapping


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Session: 11

The coverage:

•Cohen Sutherland algorithm.•Introduction to Interactive Graphics.


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Under this, we divide the LINE CLIPPING PROCESS into two phases:1.Identify those lines which intersects the clipping window and so need to be clipped and,2.Performed the clipping.

All lines fall into one of the following clipping categories:1.Visible:Both endpoints of the line within window2.Not Visible:The line definitely lies outside the window.This will occur if the line from(x1,y1)to(x2,y2)satisfies any one of the following four inequalities. X1,X2>Xmax y1,Y2>ymin X1,X2<Xmin Y1,Y2<Ymin 3.Clipping Candidate: The line is neither 1 or 2.

Cohen Sutherland Algorithm


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Pictorial View: Coheb Sutherland Algorithm


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There are commonly interactive graphics devices are as follows:

1.Key-Board.2.TOUCH PANELS.3.Light Pen.4.Graphics Tablet.5.Joystick.6.Mouse.8.Voice System.



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Session: 12

The Coverage:•Interactive Graphics Techniques.

* Introduction of GKS.


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Several techniques are used to aid the effectiveconstruction of pictures.

These are:•Constraints.•Grids.•Gravity Field.•Rubber Band Method.•Sketching.•Dragging.•Inking and painting.

Interactive Graphical Technique


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GKS(GRAPHICS KERNEL SYSTEM) was developed in to need for a standardized method of developing program.It represents a standard graphics interface with consistent syntax.Furthermore,GKS was designed so that it may be bound by means of subroutines to most common prog.Languages such as ,C,FORTRAN77,PASCAL, and BASIC.

Graphical Kernel System

Introduction:


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Session: 13

The Coverage:•GKS primitives.•GKS AS programming Language.


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The graphics kernel System is based on four basic primitives:

•POLYLINE

•POLYMARKER

•FILL AREA

•TEXT

GKS primitive attributes


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Syntax:

POLYLINE(n,x,y)

POLIMARKER(N.X,Y)

FILL AREA(N,X,Y)where n = number of data points.

X= X array.Y = Y array.

TEXT (X,Y,”String)

Primitive basics:


Computer Graphics


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SESSION - 1


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Index• Introduction of Computer and Graphic• Introduction of Computer Graphic• Area of Computer Graphic

• General• Special

• Types of Computer Graphic• Passive Graphics• Interactive graphics

• View of Interactive GraphicsL1-1


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Introduction of Computer and Graphic

• Computer: -• Hardware• Software

• Graphics:- • Images• Animation• Picture• Movies and figures,

e.t.c

L1-2


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Introduction of Computer Graphic

The Object which is lies between the different Coordinates. Computer Graphics is the Intermediary between the Application Model[program] and display HARDWARE that effects an output transformation from the objects In the application model to view of the model.

L1-3


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Area of Computer Graphic

• General

• Special

L1-4


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General

• Industry• Medical• Business• Government• Education and training• Entertainment• Defense• Home• Agriculture

L1-5


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Special

• Mathematical

• Ele. Industry

• Statistical

• Finance

• Government

• Defense

• Art and Design

L1-6


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Types of Computer Graphic

• Passive Graphic

• Interactive Graphic

L1-7


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Passive Graphics

A Computer Graphics Operation that transforms automatically and Without operator intervention.

L1-8


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As per the framework, a computer receives input from interaction devices, and output images to a display device. L1-9


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The S/W has 3 components:

1) Application Program: It Creates, Stores, and retrieves the input.

2) Application Model: It is a combination of object, data and relationship.

3) Graphics System: This is responsible for actually producing the picture from the detailed descriptions.

L1-1 0


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Conceptual framework forInteractive Graphics:

GraphicsSystem

ApplicationModel

ApplicationProgram

Display Device/PC

L1-11


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View of Interactive Graphics

• Geometric Graphic: -» Explicit Declaration» Select Criteria for insertion.

• NonGeometric Graphics: -» Implicit Declaration» Simple way of Insertion.

L1-12


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Summary

L1-13


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• Introduction of Computer and Graphic• Introduction of Computer Graphic• Area of Computer Graphic

• General• Special

• Types of Computer Graphic• Passive Graphic• Interactive graphic

– Application Model– Application programming– Computer Graphic

• View of Interactive Graphic

L1-14


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Questions

L1-15


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Question 1.

What do you mean by Computer Graphics? State its classification and outline the differences among these along with their application areas.

L1-16


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Question 2.

What are the various types of Computer Graphics? And where they are used?

L1-17


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Question 3.

Explain the Framework of Interactive Graphics?

L1-18


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SESSION - 2


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Index•Advantages of Computer Graphics.

•Usage of Computer Graphics.

•Overview of Display Devices.

» Monitors» Tubes» CRT’s» Random and Raster Scan


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Advantages of Interactive Graphics

• Most Efficient way of communication

• Expressive way of presentation

• Interactive C.G


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• Dynamic way of Picturing and fast processing.

• Update Dynamically

• High quality


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• User Interfaces • Interactive plotting in business,Science and Technology.

• Office automation and E-Publishing.

• Computer-aided and Design

Usage of Computer Graphics:


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•Simulation and animation for scientific visualization and entertainment.

•Art and Commerce.•Process Control.•Cartography.


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Overview of Display Devices.

• Monitors– Tubes

• Printers


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Monitors

• Tubes– Refresh CRT.

• Random and Raster Scan Monitor.

• Color CRT Monitors.


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Tubes• Refresh CRT: - The Primary Device in a graphic system is a

video monitor. The operation of most video monitors is based on the standard cathode-ray tube (CRT) design, but several other technologies exist and solid-state monitors may eventually predominate.


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Refresh CRT:

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.

Figure: Basic Design of a magnetic-deflection CRT


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Operation of an electron gun with an acceleration anode

The focusing system in a CRT is needed to force the electron beam to converge into a small spot as it strikes the phosphor.


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Electrostatic deflection of the electron beam in a CRT

Figure 2.4: Electrostatic deflection of the electron beam in a CRT

Spots of light are produced on the screen by the transfer of the CRT beam energy to the phosphor.


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Intensity distribution of phosphor spot on a CRT screen

• Different kinds of phosphors are available• Besides color, a major difference between

phosphors is their persistence:– how long they continue to emit light

(excited electrons)– Persistence is defined as the time it

takes the emitted light from the screen to decay to one-tenth of its original intensity.


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1. the intensity distribution of a spot on the screen. The intensity is greatest at the center of the spot, and decreases with a Gaussian distribution out to the edges of the spot. This distribution corresponds to the cross-sectional electron density distribution of the CRT beam.

2. Another property of video monitors is aspect ratio. The ratio of vertical points to horizontal points necessary to produce equal-length lines in both directions on the screen. An aspect ratio of 3/4 means that a vertical line plotted with three points has the same length as a horizontal line plotted with four points.


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Random-ScanWhen operated as 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. Random-scan monitors draw a picture one line at a time and for this reason are also referred to as Vector Display.


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Architecture of Random Scan System

System Bus

I/O DEVICES

CPUSystemMemory

Display Processor

Monitor


92

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.Picture definition is stored in a memory area called the refresh buffer or frame buffer. This memory area holds the set of intensity values for all the screen points.

Raster Scan System


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Architecture of Raster Scan System

System Bus

I/O DEVICES

CPUSystemMemory

Display Processor

Monitor

DisplayProcessor

Memory

SystemMemory

VideoController


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Random-Scan and Raster-Scan

• Random-Scan: » Electron Beam directed only to the parts of the

screen where a Picture is drawn.» 60 Frames Per Second» A pen plotter operates in a similar way.» Example: Hard-Copy Device.

• Raster-Scan:» Based Upon Television technology» Electron beam is swept across the Screen, one row

at a time from top to bottom.» Each Pixel is Plotted into the Pixel.» Example: Printer


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In Some raster scan Systems(TV sets etc.) each frame is displayed into passes using an interlaced refresh procedure.In 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. Interlacing of the scan lines allows us to see the entire screen displayed in one half of the time and used with SLOWER REFRESHING RATES.

With Interlacing , each of the two passes can beaccomplished in 1/60th of a second.which brings the refresh rates nearer to 60 frames/second. This is the effecting Technique for avoiding flicker.

Interlacing


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Questions


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Question 1.

What are Raster-Scan Graphic Systems? How does Raster-Display Processor play an important role in its functioning? Explain.


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Question 2.

Write a short note on 1) i) Random scan monitors2) ii) Raster scan monitors


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Question 3.

Explain the working of CRT ? What are the primary components of CRT?

What are the needs of CRT refreshing?


Lecture - 3


101

Index• Color CRT.

• Shadow CRT

• DVST(Direct-View Storage Tubes)

• Shadow Masking

• Flat Panel Display

• LED(Light Emitting Diode)

• LCD


102

A

Color CRT Monitors A CRT Monitors displays color pictures by using a combination of phosphorus that emit different colored light.

A range of different color displays with CRT are the beam penetration method and shadow Masking.

Beam penetration method has been used with a random scan monitors.


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Two layers of phosphor: RedGreen

Its an inexpensive way to produce color in random scan monitors and qualities of pictures is not as Good as with other Methods.


104

Shadow Masking


105

• the intensity levels of the three electron beams.• Red• Green

• The color we see depends on the amount of excitation of the red, green, and blue phosphors.

• A white (or gray) area is the result of activating all three dots with equal intensity. Yellow is produced with the green and red dots only, magenta is produced with the blue and red dots, and cyan shows up when blue and green are activated equally.


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• Color graphics systems can be designed to be used with several types of CRT display devices.– inexpensive home-computer systems and video

games– Example: - TV set and an RF (radio-frequency)

modulator. – These display devices still require that the

picture information be combined.• High-quality raster-graphics systems have 24 bits

per pixel in the frame buffer, allowing 256 voltage settings for each electron gun and nearly 17 million color choices for each pixel.


107

Maintaining a screen image is to store the picture the picture information inside the CRT.

Picture information as a charge distribution just behind the phosphor-coated screen.

Two Electron guns are used in a DVST: - I. Primary gun is used to store

the picture pattern.II.The flood gun,maintain the

picture display.

Direct -View Storage Tubes


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They Don’t display colors and that selected parts of a picture cannot be erased.

To eliminate a picture,the entire screen must be erased and the modified picture redrawn.


109

Flat-Panel Displays

• A class of video devices that have reduced volume, weight, and power requirements compared to a CRT.

• Feature of flat-panel displays: -– thinner than CRTs– Example: - pocket notepads and small TV monitors,

calculators, pocket video games, laptop computers, advertisement boards in elevators, etc.

– We can separate flat-panel displays into two categories:• emissive displays: - devices that convert electrical

energy into light.• Non emissive displays: -Use optical effects to

convert sunlight or light from some other source into graphics patterns. Example: liquid-crystal device.


110

Basic design of a plasma-panel display device


111

Basic design


112

Light-emitting Diode (LED)

• A matrix of diodes is arranged to form the pixel positions in the display, and picture definition is stored in a refresh buffer.

• The refresh buffer and converted to voltage levels that are applied to the diodes to produce the light patterns in the display.


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• Liquid-crystal displays (LCDs) are commonly used in small systems, such ' as calculators, portable, laptop computers.

• These non-emissive devices produce a picture by passing polarized light from the surroundings or from an internal light source through a liquid-crystal material that can be aligned to either block or transmit the light.

Liquid-crystal Displays (LCD’s)


114

A hand calculator with an LCD screen


115

The light-twisting, shutter effect used in the design of most liquid-

crystal display devices


116

Question


117

Question -1Give the advantages and

disadvantages of hard copy displays, DVST displays, vector refresh displays and raster displays. Suggest an application area for which each class of device is best suited.


118

Question – 2Why is the electron beam allowed to overscan? Also discuss about the technique which involves splitting a raster-scan pattern into separate patterns.


119

Question – 3What are Raster-Scan Graphic Systems? How does Raster-Display Processor play an important role in its functioning? Explain.


120

Question - Differentiate the working principles of

LCD and Plasma Panel Displays.


SESSION – 4


122

INDEX

• Hard Copy Device • Laser Printer• Ink – Jet Printer.• Electrostatic device Place

• Pen Plotter.


123

Hard Copy Device• We can obtain hard-copy output for our

images in several formats.• To put images on film, we can simply

photograph a scene displayed on a video monitor.

• 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.

• A line printer is an example of an impact device, with the typefaces mounted on bands, chains, drums, or wheels.


124

A picture generated on a dot-matrix printer showing how the density of the dot patterns can be varied to produced light and dark areas


125

Laser Printer• Laser beam creates a

charge distribution on a rotating drum coated with a photoelectric material.

• Toner is applied to the drum and then transferred to paper.

• examples of desktop laser printers with a resolution of 360 dots per inch.


126

INK – JET METHOD

• Ink-jet methods produce output by squirting ink in horizontal rows across a roll of paper wrapped on a drum.

• The electrically charged ink stream is deflected by an electric field to produce dot-matrix patterns.

• A desktop ink-let plotter with a resolution of 360 dots per inch.


127

Electrostatic Device Places• An electrostatic device places- a

negative charge on the paper, one complete row at a time along the length of the paper. Then the paper is exposed to a toner The toner is positively charged and so is attracted to the negatively charged areas, where it adheres to produce the specified output.

• A color electrostatic printer/plotter is shown in Figure 2.19. Electro thermal methods use heat in a dot- matrix print head to output patterns on heat-sensitive paper.


128

Pen Plotter

• A pen plotter has one or more pens mounted on a carriage, or crossbar, that spans a sheet of paper.

• Pens with varying colors and widths are used to produce a variety of shadings and line styles. Wet-ink, ball-point, and felt-tip pens are all possible choices for use with a pen plotter.

• Plotter paper can lie flat or be rolled onto a drum or belt. Crossbars can be either moveable or stationary, while the pen moves back and forth along the bar.


129

Question


130

Question -1

Write a short note on hard copy devices.


131

Question -2

Discuss the detailed of DVST.


SESSION - 5


133

INDEX

• Introduction• Scan-converting a Point• Scan-converting a Straigh Line


134

INTRODUCTION – Converting binary values stored.

• pixel-on

• pixel-off information.

– More Complex graphics objects

• Points

• Lines

• Circles

• Ellipses.


135

• Human users with fast

• Memory-efficient routines

• The process of representing continuous graphics objects as a collection of discrete pixels is called scan conversion

• Many scan-conversion algorithms are implemented in computer hardware or firmware.

• The most commonly used graphics objects are line, the sector, the arc, the ellipse, the rectangle and the polygon.


136

Scan - Converting a Point• A mathematical point (x, y) where x and y are real

numbers. x’ = Floor(x) and y’ = Floor(y), x’ < x < x’ + 1 and y’ < y < y’ + 1 are mapped to pixel (x’ y’).

• Here we scan convert (x, y)

x’ = Floor(x + 0.5) and y’ = Floor(y + 0.5).


137

Scan - Converting a Straight Line

• The two endpoints are described by (x1, y1) and (x2, y2).

• Using the equation of a straight line, y = mx + b where m = Δy/Δx

and b = the y intercept,• Interactive graphics is a graphics system in which

the user dynamically controls the presentation of graphics models.


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THE LINE


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Direct Use Of Line Equation1) First scan-convert P1 and P2 to pixel coordinates

(x’1, y’1) and (x’2, y’2), respectively;

2. then set m = (y’2 - y’1) / (x’2 - x’1) and

b = y’1 –mx’1.

2. If |m| > 1, then for every integer value of y between and excluding y’1 and y’2 calculate the corresponding value of x using the equation and scan-convert (x, y).

• While this approach is mathematically sound, it involves floating-point computation


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Example


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E1. The endpoints of a given line are (0, 0) and (6, 18).

Compute each value of y as x steps from 0 to 6 and plot the

results.An equation for the line was not given.

(y = mx + b) • y = 3x +b: 0 = 3(0) + b. Therefore, b = 0, so

the equation for the line is y = 3x


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E2. What steps are required to plot a line whose slope is

between 0o and 45o using the slope-intercept equation

1. Compute dx: dx = x2 - x1.

2. Compute dy: dy = y2 – y1.

3. Compute m: m = dy/dx.4. Compute b: b = y1 – m x1.


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5. Set (x, y) equal to the lower left-hand endpoint and set xend equal to the largest value of x. If dx < 0, then x = x2, y = y2, and xend = x1. If dx > 0, then x = x1, y = y1, and xend = x2.

6. Test to determine whether the entire line has been drawn. If x > xend, stop.

7. Plot a point at the current (x, y) coordinates.


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8.Increment x: x = x + 1.9.Compute the next value of y from the

equation y = mx + b.10. Go to step 6.


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Use pseudo-code to describe the steps that are required to plot a line whose slope is between 45o and –45o (i.e., [m] > 1) using the

slope-intercept equation.• Presume y1 < y2 for the two endpoints (x1 , y1) and (x2, y2):

• int x = x1, y = y1;

• float xf, m = (y2 – y1)/(x2 - x1), b = y1 = mx1;

• Set Pixel (x, y);• while (y < y2); y++;

• xf = (y – b)/m; x = Floor(xf + 0.5);

• Set Pixel (x, y);}


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Question


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Question -1

How is the point displayed on the graphics scale?

Documents

An ISO 9001:2008 Certified Organization PCTI Group Computer Graphics By : Pcti Group