unit-1-basics-of-computer-graphics.ppt 7th sem

Basics of
Basics of
Computer Graphics
Computer Graphics

Computer Graphics is about animation (films)
Major driving force now

Computer graphics
• It is the creation and manipulation of graphic
images by means of a computer.
 Computer graphics started as a technique to
enhance the display of information generated
by a computer.
 This ability to interpret and represent
numerical data in pictures has significantly
increased the computer’s ability to present
information to the user in a clear and
understandable form.
 Large amount of data are rapidly converted
into bar charts, pie charts, and graphs.

4
Pixel (picture element)
a pixel is the smallest piece of information in an
image.
 Pixels are normally arranged in a regular 2D
grid, and are often represented using dots or
squares.

5
Pixel (picture element)
 Each pixel is a sample of an original image,
where more samples typically provide a more
accurate representation of the original.
 The intensity of each pixel is variable; in color
systems, each pixel has typically three or four
components such as red, green, and blue, or
cyan, magenta, yellow, and black.

Resolution
• Resolution is the number of rows that appear from
top to bottom of a screen and in turn the number of
pixels or pixel elements that appear from left to right
on each scan line.
• Based on this resolution only the effect of picture
appears on screen.
• In other words greater the resolution greater will be
the clarity of picture. That is resolution value is
directly proportional to clarity of picture.

• Actual resolution is determined by the video controller.
– Most monitors can operate at several different resolutions.
They are
– 640 X 480
– 800 X 600
– 1024 X 768
– 1152 X 864
– 1280 X 1024
• As the resolution increases, image on the screen gets
smaller.

1) Image Resolution: It refers to pixel spacing. In
normal PC monitor it ranges between 25 to 80 pixels per
inch.
2) Screen Resolution: It is the number of distinct pixels in
each dimension that can be displayed.
For example, a computer with a display resolution of
1280 x 768 will produce a maximum of 98,3040 pixels on
a display screen. Each pixel has a unique logical address,
a size of eight bits or more and, in most high-end display
devices, the ability to project millions of different colors.

Text mode
• Text mode is a personal computer display setting
that divides the display screen into 25 rows and
80 columns in order to display text without
images.
• In text mode, each box can contain one
character. Text mode contrasts with graphics
mode, which features an array of pixels instead of
text boxes.
• Text mode is also known as character mode or

Graphics mode
• Graphics mode is a computer display mode
that generates image using pixels.
• Today, most users operate their computer in a
graphics mode opposed to a text mode or
command line environment.

Graphics mode graphics Function
• GRAPHICS.H ,this file contains definitions and explanati
of all the graphic functions and constants. While
GRAPHICS.LIB file contains standard graphic functions.
• InitGraph:
• Initializes the graphics system.
Declaration:
void initgraph(int *graphdriver, int *graphmode, char *pathtodriver);
eg: void initgraph(&gd,&gm,”path of bgi file”);
initgraph(&gd,&gm,"c:turboc3bgi");

Initgraph Arguments:
• *graphdriver: Integer that specifies the graphics driver
to be used.
• *graphmode : Integer that specifies the initial graphics
mode. If *graphdriver = DETECT, initgraph sets
*graphmode to the highest resolution available for the
detected driver.
• pathtodriver : Specifies the directory path where
initgraph looks for graphics drivers (*.BGI) first.

A graphics pipeline
• A graphics pipeline can be divided into three
main parts: Application, Geometry and
Rasterization.

Application
• The application step is executed by the software
on the main processor (CPU), it cannot be divided
into individual steps, which are executed in a
pipelined manner.
• In the application step, changes are made to the
scene as required, for example, by user
interaction by means of input devices or during
an animation.
• The new scene with all its primitives, usually
triangles, lines and points, is then passed on to
the next step in the pipeline.

Geometry
• The geometry step is responsible for the majority of
the operations with polygons and their vertices ,
can be divided into the following five tasks.
• It depends on the particular implementation of how
these tasks are organized as actual parallel pipeline
steps.
object

Rasterization
• Rasterization is the task of taking an image
described in a vector graphics format (shapes)
and converting it into a raster image (pixels or
dots) for output on a video display or printer,
or for storage in a bitmap file format. It refers
to both rasterization of models and
2D rendering primitives such as polygons, line
segments, etc.

Bitmapped Graphics
• There are two basic types of graphics:
– Bitmapped and
– Vector
• Bitmapped graphics are much more common
• Often they are called raster graphics
• When you create a bitmapped graphic you are
basically creating a bunch of colored dots

Bitmapped Graphics, cont.
• The bitmapped graphic is stored as an array of dots, or pixels
• Each pixel gets assigned a specific color
• The more pixels you have, the more detailed the image can
be
– Imagine only have one pixel, all you get is a dot
• Some common bitmap graphics programs are:
– Photoshop
– Paint Shop Pro
– GIMP
– Photo-Paint
– Graphic Converter
• These are paint programs

Exaggerated Example of a Bitmap Image

Vector Graphics
• The second major type of computer graphics
• Vector graphics are created and manipulated using drawing
programs (as opposed to paint programs for bitmapped
graphics)
• Instead of using pixels to describe the image, it describes the
image using shapes
– Circles
– Lines
– Curves
• Also has to store the color of these shapes
• A verbal example would be something like:
– “A yellow circle with a center here and a radius of x, a purple line from
here to here”

Vector Graphics, cont.
• The programs used with vector graphics are drawing
programs
• Some of these programs include:
– Corel Draw
– Adobe Illustrator
– Acrobat
• Most of these programs allow the use of bitmapped
images as part of a vector image
– Does not make them paint programs
– Bitmaps are a type of object (like a circle) that can be
inserted into a vector image

Bitmap vs. Vector Images
• Bitmap and vector images are obviously
different
• Both have strengths and weaknesses
• They don’t manipulate images in the same
way
• They don’t store images in the same way
• The images are edited differently

24
Applications of Computer Graphics
•Computer graphics user interfaces (GUIs) − A
graphic, mouse-oriented paradigm which allows
the user to interact with a computer.
•Business presentation graphics − "A picture is
worth a thousand words".
•Cartography − Drawing maps.
•Weather Maps − Real-time mapping, symbolic
representations.
•Satellite Imaging − Geodesic images.

• Photo Enhancement − Sharpening blurred
photos.
• Medical imaging − MRIs, CAT scans, etc. -
Non-invasive internal examination.
• Engineering drawings − mechanical, electrical,
civil, etc. - Replacing the blueprints of the
past.
• Architecture − Construction plans, exterior
sketches - replacing the blueprints and hand
drawings of the past.
• Art − Computers provide a new medium for
artists.
• Entertainment − Movies and games.
• Simulation and modeling − Replacing physical
modeling and enactments

Type of Display Device
• Type of CRT
– Random-Scan Displays
– Raster-Scan-Displays
• Flat-Panel Displays
– Emissive displays
– Nonemissive displays

Video Display Devices
• Cathode-Ray Tube(CRT)
(cathode ray)

Random-Scan Display
– Vector Display (calligraphic display)
– stored as a set of line-drawing commands in an
area of memory (refresh display file, display list,
display program)
– draw a picture one line at a time

Raster-Scan Displays (1/3)
– Point plotting device : pixel or pel (Picture
Element)
– picture info. for all the screen points is stored
in separate Memory called Frame buffer
(Refresh Buffer)
– one row at a time (scan line) from top to
bottom

Frame Buffer
• A frame buffer is
characterized by size, x, y,
and pixel depth.
• the resolution of a frame
buffer is the number of
pixels in the display. e.g.
1024x1024 pixels.
• Bit Planes or Bit Depth is the
number of bits
corresponding to each pixel.
This determines the color
resolution of the buffer.
Bilevel or monochrome displays
have 1 bit/pixel
8bits/pixel -> 256 simultaneous colors
24bits/pixel -> 16 million simultaneous
colors

• Frame buffer
– Depth of the buffer area, Number of bit planes
– Bitmap: one bit per pixel
– Pixmap: multiple bits per pixel
• Refresh rate
– Above about 24 frame per second
– Unit of refresh rates  Hz
• Ex) 60 frames per second (60Hz)

• Picture definition is stored in memory area called the Refresh
Buffer or Frame Buffer.
• This memory area holds the set of intensity values for all the screen
points. Stored intensity values are then retrieved from the refresh buffer
and “painted” on the screen one row (scan line) at a time as shown in the
following illustration.

Raster Displays (Bitmap)
• Intensity for each pixel depends on the size of
frame buffer
– ex) Black & White system
one bit per pixel is needed
the frame buffer is commonly called
Bitmap

Raster Displays (Pixmap)
– With multiple bits per pixel, we can display gray-
scale or color pictures
the frame buffer is commonly called pixmap
Ex) Size of Frame Buffer when N=3, with 512 X 512
Size of Frame buffer = 3 X 512 X 512 = 3 X 256k = 768k

unit-1-basics-of-computer-graphics.ppt 7th sem

Flat Panel Display
What does Flat Panel Display mean?
A flat panel display is a television, monitor or other
display appliance that uses a thin panel design instead
of a traditional cathode ray tube (CRT) design.
These screens are much lighter and thinner, and can
be much more portable than traditional televisions and
monitors. They also have higher resolution than older
models.

LED display
Light-emitting diode (LED)
• An LED display is a flat panel display,
which uses an array of light-emitting
diodes as pixels for a video display.
• In recent years they have also become commonly used in destination
signs on public transport vehicles, as well as variable-message signs on
highways.
• LED displays are capable of providing general illumination in addition to
visual display.

• The first true all-LED flat panel television screen
was possibly developed, demonstrated and
documented by James P. Mitchell in 1977.
•

• The LED is a PN-junction diode which emits light when
an electric current passes through it in the forward direction.
In the LED, the recombination of charge carrier takes place.
• The electron from the N-side and the hole from the P-side are
combined and gives the energy in the form of heat and light.
The LED is made of semiconductor material which is
colourless, and the light is radiated through the junction of
the diode.
• The LEDs are extensively used in segmental and dot matrix
displays of numeric and alphanumeric character.
• The several LEDs are used for making the single line segment
while for making the decimal point single LED is used.

Working of LED
• The working of the LED depends on the quantum theory.
• The quantum theory states that when the energy of electrons decreases
from the higher level to lower level, it emits energy in the form of photons.
• The energy of the photons is equal to the gap between the higher and
lower level.

Working of LED
• The LED is connected in the forward biased, which
allows the current to flows in the forward direction.
• The flow of current is because of the movement of
electrons in the opposite direction.
• The recombination shows that the electrons move
from the conduction band to valence band and they
emits electromagnetic energy in the form of
photons.
• The energy of photons is equal to the gap between
the valence and the conduction band.

Applications of Light Emitting Diodes
•LED is used as a bulb in the homes and industries
•The light emitting diodes are used in the motorcycles and cars
•These are used in the mobile phones to display the message
•At the traffic light signals led’s are used.
Advantages of LED’s
•The cost of LED’s is less and they are tiny.
•By using the LED’s the electricity is controlled.
•The intensity of the LED differs with the help of the microcontroller.
•The LED are available which emits light in the different colors like red, yellow,
green and amber.
Disadvantages of LED
•The LED consume more power as compared to LCD, and their cost is high. Also,
it is not used for making the large display.

Liquid-crystal display
(LCD)
• It is combination of two states of matter, the solid and
the liquid.
• LCD uses a liquid crystal to produce a visible image.
• Liquid crystal displays are super-thin technology display
screen that are generally used in laptop computer
screen, TVs, cell phones and portable video games.
• LCD’s technologies allow displays to be much thinner
when compared to cathode ray tube (CRT) technology.

Simple facts that should be considered while making an LCD:
• The basic structure of LCD should be controlled by changing the
applied current.
• We must use a polarized light.
• Liquid crystal should able be to control both of the operation to
transmit or can also able to change the polarized light.

Advantages of an LCD’s:
•LCD’s consumes less amount of power compared to CRT and LED
•LCDs are of low cost
•Provides excellent contrast
•LCD’s are thinner and lighter when compared to cathode ray
tube and LED
Disadvantages of an LCD’s:
•Require additional light sources
•Range of temperature is limited for operation
•Low reliability
•Speed is very low
Applications of Liquid Crystal Display
•Liquid crystal thermometer ,Optical imaging, Used in the medical
applications

Plasma Display Panel (PDP)
• A plasma display panel (PDP) is a type of flat panel
display common to large TV displays 30 inches (76 cm) or
larger.
• They are called "plasma" displays because they use
small cells containing electrically charged ionized gases,
which are plasmas.
• Plasma displays are thinner than cathode ray tube
( CRT ) displays and brighter than liquid crystal
displays ( LCD).

Touch Screen
• A touch screen is a computer display screen that
is also an input device. The screens are sensitive
to pressure; a user interacts with the computer
by touching pictures or words on the screen.
• There are three types of touch screen
technology:
 Resistive
 Surface wave
 Capacitive

Output primitives
• The Primitives are the simple geometric
functions that are used to generate various
Computer Graphics required by the User.
Some most basic Output primitives are point-
position(pixel), and a straight line.
• Line , polygon , marker , text

LINE ATTRIBUTES
• A straight-line segment can be displayed with
three basic attributes: color, width, and style.
• Line color is typically set with the same
function for all graphics primitives, while line
width and line style are selected with separate
line functions.
• Additionally, lines may be generated with
other effects, such as pen and brush strokes.

To set line type attributes in a PHICS application
program, a user invokes the function
setLinetype (It)
where parameter I t is assigned a positive integer
value of 1,2,3, or 4 to generate lines that are,
respectively, solid, dashed, dotted, or dash-dotted.

Functions Of graphics.h
• C graphics using graphics.h functions can be
used to draw different shapes, display text in
different fonts, change colors and many more.
• Using functions of graphics.h in Turbo C
compiler you can make graphics programs,
animations, projects, and games.
• You can draw circles, lines, rectangles, bars
and many other geometrical figures. You can
change their colors using the available
functions and fill them.

void circle(int x, int y, int radius);
Circle function is used to draw a circle with center (x,y)
and third parameter specifies the radius of the circle. The
code given below draws a circle.
void closegraph();
closegraph function closes the graphics mode, deallocates
all memory allocated by graphics system and restores the
screen to the mode it was in before you called initgraph.

Virtual Reality
• Virtual reality (VR) means experiencing things through
our computers that don't really exist.
• A believable, interactive 3D computer-created world that you can
explore so you feel you really are there, both mentally and
physically.
Putting it another way, virtual reality is essentially:
• Believable: You really need to feel like you're in your virtual world
and to keep believing that, or the illusion of virtual reality will
disappear.

• Interactive: As you move around, the VR world needs to
move with you. You can watch a 3D movie and be
transported up to the Moon or down to the seabed—but it's
not interactive in any sense.
• Computer-generated: Only powerful machines, with realistic
3D computer graphics, are fast enough to make believable,
interactive, alternative worlds that change in real-time as we
move around them.
• Explorable: A VR world needs to be big and detailed enough
for you to explore.
• Immersive: To be both believable and interactive, VR needs
to engage both your body and your mind. Paintings by war
artists can give us glimpses of conflict, but they can never
fully convey the sight, sound, smell, taste, and feel of battle.

Types of VR System
 Windows on World(WoW)
– Also called Desktop VR.
– Using a conventional computer monitor to display the
3D virtual world.
 Immersive VR
– Completely immerse the user's personal viewpoint
inside the virtual 3D world.
– The user has no visual contact with the physical world.
– Often equipped with a Head Mounted Display (HMD).
57

Types of VR System(Cont’d)
 Telepresence
– A variation of visualizing complete computer
generated worlds.
– Links remote sensors in the real world with the senses of a
human operator. The remote sensors might be located on a
robot. Useful for performing operations in dangerous
environments.
58

Types of VR System(Cont’d)
 Mixed Reality(Augmented Reality)
– The seamless merging of real space and virtual space.
– Integrate the computer-generated virtual objects into the
physical world which become in a sense an equal part of our
natural environment.
59

VR Examples (Cont’d)
Distributed VR
– A simulated world runs on several computers which are
connected over network and the people are able to interact in
real time, sharing the same virtual world.
60

Architecture of VR System
 Input Processor, Simulation Processor,
Rendering Processor and World
Database.
61
Input
Processor
Rendering
Processor
World Database
Simulation
Processor
visual,
auditory,
haptic,
touch…
Position &
Orientation

Components of VR System (Cont’d)
 Input Processor
– Control the devices used to input information
to the computer. The object is to get the
coordinate data to the rest of the system with
minimal lag time.
– Keyboard, mouse, 3D position trackers, a
voice recognition system, etc.
62

63
 Simulation Processor
– Core of a VR system.
– Takes the user inputs along with any tasks
programmed into the world and determine
the actions that will take place in the virtual
world.

64
 Rendering Processor
– Create the sensations that are output to
the user.
– Separate rendering processes are used for
visual, auditory, haptic and other sensory
systems. Each renderer take a description
of the world stat from the simulation
process or derive it directly from the World
Database for each time step.

65
 World Database (World Description
Files)
– Store the objects that inhabit the world,
scripts that describe actions of those
objects.

Technologies of VR--Hardware
 Head-Mounted Display (HMD)
 A Helmet or a face mask providing the visual and auditory
displays.
 Use LCD or CRT to display stereo images.
 May include built-in head-tracker and stereo headphones
66

 Binocular Omni-Orientation Monitor (BOOM)
 Head-coupled stereoscopic display device.
 Uses CRT to provide high-resolution display.
 Convenient to use.
 Fast and accurate built-in tracking.
67

 Cave Automatic Virtual Environment (CAVE)
 Provides the illusion of immersion by projecting stereo
images on the walls and floor of a room-sized cube.
 A head tracking system continuously adjust the stereo
projection to the current position of the leading viewer.
68

 Data Glove
– Outfitted with sensors on the fingers as well as an overall
position/orientation tracking equipment.
– Enables natural interaction with virtual objects by hand gesture
recognition.
69

Applications
 Entertainment
– More vivid
– Move exciting
– More attractive
70

Applications (Cont’d)
 Medicine
 Practice performing surgery.
 Perform surgery on a remote patient.
 Teach new skills in a safe, controlled environment.
71

 Manufacturing
– Easy to modify
– Low cost
– High efficient
72

 Education & Training
– Driving simulators.
– Flight simulators.
– Ship simulators.
– Tank simulators.
73

What Is Augmented Reality (AR)?
• A combination of
– a real scene viewed by a
user and
– a virtual scene
generated by a
computer that augments
the scene with
additional information.
– ARToolkit demo movie
– T-immersion 2004 video

What is AR? (cont.)
• Ronald Azuma defines an augmented reality system
as one that:
– Combines real and virtual world aspects
– Is interactive in real-time
– Is registered in three dimensions

• Virtual Reality (VR)
a computer generated, interactive, 3D environment
in which a person is immersed : virtual, interactive
and immersive
• Augmented Reality (AR)
Supplements the real world with the
virtual(computer generated) objects that appear to
coexist in the same space as the real world.
Virtual Reality vs. Augmented Reality

Augmented Reality vs. Virtual Reality
Augmented Reality
• System augments the
real world scene
• User maintains a sense
of presence in real world
• Needs a mechanism to
combine virtual and real
worlds
• Hard to register real and
virtual
Virtual Reality
• Totally immersive
environment
• Senses are under
control of system
• Need a mechanism to
feed virtual world to
user
• Hard to make VR world
interesting

Engineering Education –Virtual Storm
Augmented Reality vs. Virtual Reality

What is needed?
• There are three components needed in order to make an
augmented-reality system work:
– Head-mounted display
– Tracking system
– Mobile computing power

Current Uses of AR
• Yellow first down line used
on TV broadcasts of football
games:
– Real world elements:
football field and players
– Virtual element: the yellow
line drawn over the image
by computers in real-time

Current Uses of AR
• HUD (Head Up Display):
– Used in commercial
aircraft, automobiles, and
other applications
– Presents data without
requiring the user to look
away from his or her usual
viewpoint

LifeClipper
• LifeClipper is a wearable AR
system being used in
Switzerland.
• When walking around a
chosen culturally interesting
area, the user will feel as
though they are watching a
film.

Wikitude – AR Travel Guide
• Mobile travel guide for the
Android platform (open source
OS for cell phones).
• Plan a trip or find about
current surroundings in real-
time.

Future of AR
• Military:
– The Office of Naval Research has sponsored AR research
– AR system could provide troops with vital information about their
surroundings.
• Medical:
– Superimpose an image from an MRI onto a patient’s body.
– This might allow surgeons to pinpoint a tumor to remove.
• Education:
– Used in labs where students can learn more about the experiments
they are participating in.

Future of AR
• Gaming:
– ARQuake is an AR version of the
popular game Quake.
• 1st
person shooter that
allows the user to run
around in the real world
while playing a game in the
computer generated world.
• Uses GPS, a hybrid magnetic
and interial orientation
sensor, gun controller, and a
standard laptop carried in a
backpack.

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