unit1_updated.pptx

INTRODUCTION TO
COMPUTER GRAPHICS &
OPENGL

ADMINISTRATION
 Total number of lectures: 24 (Synchronous)+12
(Asynchronous)+9(Doubt clearing sessions+
assessment sessions) (3 credit course)
 Mid Sem- 20%
 End Sem- 50%
 IA- 30%
 2 Class tests - 30% (One before mid term and one
before end term)
 2 quiz – 30% (One before mid term and one before end
term)
 2 Assignment- 40% (One before mid term and one
before end term)

PASSING CRITERIA
 85 or above for Outstanding (O)
 35 Marks is the minimum passing marks

BOOKS/ MATERIAL
 Computer Graphics-C version by Donald Hearn &
M. Pauline Baker
 Computer Graphics with OpenGL by Donald Hearn
& M. Pauline Baker
 Mathematical elements for Computer Graphics; by
D. F. Rogers and J. A. Adams
 Procedural elements for Computer Graphics; by D.
F. Rogers and J. A. Adams
 Computer Graphics & Multimedia by D. Evangeline
& S. Anitha
 Computer Graphics byArnav N Sinha & Arun D
Udai

CONTENTS
 Overview of computer graphics
 Computer graphics application and software
 Description of graphics devices
 Introduction to pixel

INTRODUCTION
 Computer Graphics is the use of computer to define,
store, manipulate and present pictorial output.
A picture is worth a thousand words!
 Typically, the term computer graphics refers to several
different things:
 The representation and manipulation of image data by a
computer
 The various technologies used to create and manipulate images
 The sub-field of computer science which studies methods for
digitally synthesizing and manipulating visual content

Typical graphics system comprises of:
 A host computer with support of fast processor
 large memory
 Frame buffer
 Input devices (mouse, keyboard, joystick, touch
screen, etc.)
 Output devices (printers, plotters, CRT, LCDs etc.)

 Computer Graphics System could be:
 Active : User controls the display with the help of a
GUI, using an input device (ex. Videogame)
 Passive: User cannot control the display (ex.
Television)

COMPUTER GRAPHICS VS IMAGE
PROCESSING VS COMPUTER VISION
 Computer graphics referred to the process of creating
images from abstract models.
 A computer game, for example, might internally keep
track of Mario as a large list of points, where each
point has three numbers representing its (x, y, z)
coordinates. Then, given the coordinates of the
camera, and the direction its facing, the computer
will calculate the color at each row and column in the
final image of Mario that you see on your screen.

 Image processing refers to the process of starting
with an existing image and refining it in some way
to obtain another image.
 For example, if you take a picture with your camera,
you would use an image processing algorithm to try
and make the colors more vibrant, or remove the
blur, or increase the resolution. The output of an
image processing algorithm is another image.

 Computer vision, that refers to the process of
computing an abstract model given an input image.
For example, if you take a picture of a statue of Mario,
a vision algorithm would infer the list of (x, y, z)
coordinates of the points that make up Mario from the
colors at each row and column in the input image.
 Computer vision is the construction of explicit,
meaningful descriptions of physical objects from their
image. The output of computer vision is a description
or an interpretation of structures in 3D scene.

FUNDAMENTAL CONCEPTS AND PRINCIPLES IN
COMPUTER GRAPHICS
 Display Systems: Random scan, Raster refresh
displays, CRT basics, video basics, Flat panel
displays.
 Transformations
 Affine ( 2-D and 3-D ): Rotation, Translation, Scale,
Reflection and Shear.
 Viewing: The Camera Transformations: perspective,
isometric views.
 Scan Conversion and Clipping: Drawing of
Points, Lines, Markers, Curves, Circles, Ellipse,
Polyline, Polygon. Area filling, fillstyle, fill pattern,
clipping algorithms, anti-aliasing etc.

 Hidden Surface Removal: Back face culling,
Painter's algorithm, scanline algorithm, BSP-trees,
Z-buffer/sorting, Ray tracing etc.
 Shading & Illumination: Phong's shading model,
texture mapping, bump mapping, Gouraud shading,
Shadows and background, Color models etc.
 Solid Modeling: Wire-frame, Octrees, Sweep,
Boundary representations, Constructive Solid
Geometry.

 http://realsoft.fi/gallery/
 http://www.realsoft.com/tutorials/firstscene/part1.ht
m
Link to see the Realsoft 3D Tutorials

BASIC ELEMENTS OF COMPUTER GRAPHICS
 Modeling: the process of developing a
mathematical representation of any surface of an
object.
 Rendering: In 3-D graphic design, rendering is the
process of add shading, color and illumination to a
2-D or 3-D wireframe in order to create life-like
images on a screen.

 Animation: refers to the moving images.

GRAPHICS CARD AND GPU
 The graphics card is the hardware as a whole, while the
GPU is a chip, part of the graphics card or an onboard similar,
which stands for "Graphics Processing Unit".
 Graphics card is the piece of hardware that is responsible of
producing output to monitor. GPU is short from
Graphics Processing Unit.
 Graphics Card is a complete board that gets binary data
from the processor and outputs the result to the monitor
in the form of pixels. Now there are lots of components in
the Graphics card like
 GPU
 RAM (A dedicated RAM inside the graphics card used only by
the card. Not to be confused with the system RAM)
 DAC (Digital to Analog Converter) that converts the digital data
to analog format to be displayed in the monitor.

 Not Only all Laptops But all the computers having a CPU must
have a Graphic Card for basic graphic rendering functions.
 There are two types of graphics card however :
 Built-in : Inside your CPU (eg. Intel integrated graphics)
 Add-on : Additionally added for more graphic intensive tasks (eg.
Nvidia Ge force series)
 Some small scale computers (eg. Calculators etc.. ) do not
require a graphic card and they don’t have one either.
 All laptops come with built in graphics card be it Integrated or
Dedicated.
 Integrated graphics is basically a graphics processing unit
which does not have it's own memory but uses a little amount
of the system memory.

 It can be a part of the chipset or the CPU and is sufficient for
an average user.
 Dedicated graphics card have their own memory. Say you
have a GeForce GTX 550 Ti with 1GB of memory, it'll utilize
that and not use the system memory. Such cards are used by
serious gamers and people who use graphic intensive
applications.

APPLICATIONS OF COMPUTER GRAPHICS
 GUI (Graphical User Interface)
 Typical components used:
 Menus
 Icons
 Cursors
 Dialog boxes
 Scroll bars
 Buttons
 Valuators

 Plotting in business
 Web/ business/ commercial publishing and
advertisements
 Scientific visualization

 Entertainment (movie, TV advertisement, Games
etc.)

 CAD/ CAM design (construction, circuits)
 Multimedia
 Virtual reality

 Cartography- Drawing maps
 Education and training- Flight simulators, sport
simultors, etc.
 Medical Imaging- MRIs, CT Scan, X ray

VARIOUS APIS USED FOR COMPUTER
GRAPHICS
 GKS (Graphics Kernel System)
 SRGP (Simple Raster Graphics Package)
 PHIGS (Programmers Hierarchical Interactive
Graphics System)
 OpenGL
 X-11 based systems
 Direct3D (a subset of DirectX)
 Glide API
 Mantle developed by AMD.
 Metal developed by Apple.
 QuickDraw 3D developed by Apple Computer
starting in 1995, abandoned in 1998

COMPUTER GRAPHICS SOFTWARE
 Photoshop
 Illustrator
 Blender
 Paint Shop Pro
 CorelDRAW
 Adobe Lightroom
 Realsoft
 Digital Image Suite
 Canvas
 Picasa and many more

COMPUTER GRAPHICS DEVICES
 CRT
 EGA/CGA/VGA/SVGA monitors
 Plotters
 Data matrix
 Laser printers
 Flat panel devices
 Video digitizers
 Scanners
 LCD panels
 Keyboard, joystick, mouse
 Touch screen, track ball, etc.

PIXEL
 A pixel is the smallest unit of a digital image or
graphic that can be displayed and represented on a
digital display device.
 A pixel is the basic logical unit in digital graphics.
Pixels are combined to form a complete image,
video, text or any visible thing on a computer
display.
 A pixel is also known as a picture element.

BASIC RELATIONSHIPS BETWEEN PIXELS
 Neighborhood
 Adjacency/ Connectivity
 Paths

M-ADJACENCY
 M- adjacency (Mixed adjacency): Mixed adjacency
is a modification of the 8- adjacency. It is introduced
to eliminate ambiguities of 8-adjacency.
 There are cases where 2 pixels are 8-adjacent but
not m-adjacent.

PATH & PATH LENGTH
 We can define 4-, 8-, and m-paths based on type of
adjacency used.

TYPES OF CRT DISPLAY DEVICES
 The most commonly used display device is the
CRT monitor.
 Types of CRT display devices:
 DVST (Direct View Storage Tube)
 Calligraphic or Random Scan display system
 Refresh and raster scan display system

GRAPHICS DISPLAY DEVICES (CRT)
 The primary output device in a graphical system is the
video monitor.
 The main element of a video monitor is the Cathode
Ray Tube (CRT)
 CRT : still the most common video display device
presently
 Consists of:
 Electron gun
 Electron focusing lens
 Deflection plates/ coils
 Electron beam
 Phosphorous coated screen

ELECTROSTATIC DEFLECTION OF THE
ELECTRON BEAM IN A CRT

BASIC DESIGN OF A MAGNETIC DEFLECTION
CRT

DVST (DIRECT VIEW STORAGE TUBE)
 Storage Tube- It is a CRT with a long persistence
phosphor.
 Pictures drawn on there will be seen for several minutes
before fading.
 Provides flicker-free display.
 Instead of the electron beam directly writing the pictures
on the phosphor coated CRT screen, the writing is done
with the help of a fine-mesh wire grid.
 A pattern of positive charges is deposited on the grid
and this pattern is transferred to the phosphor coated
CRT by a continuous flood of electrons.
 This flood of electrons is produced by a "flood gun"

 Just behind the storage mesh is a second grid called the
collector.
 The function of the collector is to smooth out the flow of
flood electrons.
 Since a large number of electrons are produced at high
velocity by the flood gun, the collector grid, which is also
negatively charged reduces the acceleration on these
electrons and the resulting low velocity flood pass
through the collector and get attracted by the positively
charged portions of the storage mesh (Since the
electrons are negatively charged), but are repelled by
the other portions of the mesh which are negatively
charged (Note that the pattern of positive charges
residing on the storage mesh actually defines the picture
to be displayed).

 Thus, the electrons attracted by the positive
charges pass through the mesh, travel on to the
phosphor coated screen and display the picture.
 Since the collector has slowed the electrons down,
they may not be able to produce sharp and bright
images

DRAWBACKS OF DVST
 Selected part of picture cannot be erased.
 To modify a picture the whole picture has to be
redrawn which takes lot of time in case of complex
pictures.
 Not able to produce sharp and bright images.
 No animation possible with DVST.

RANDOM SCAN DISPLAY
 Also known as Calligraphic displays, vector displays
or stroke displays.
 The CRT's electron beam is directed only to the parts
of the screen where a picture is to be drawn.
 Characters are also made of sequences of strokes
(or short lines)
 Vectored – electron beam is deflected from end-point
to end-point
 Random scan -Order of deflection is dictated by the
arbitrary order of the display commands
 Phosphor has short persistence –decays in 10-100
micro seconds.

 The display must be refreshed at regular intervals –
minimum of 30 Hz (fps) for flicker-free display
 Refresh Buffer/ Display buffer–memory space allocated
to store the display list or display program for the display
processor to draw the picture
 The display processor interprets the commands in the
refresh buffer for plotting
 To display a picture, the system cycle through the set of
commands in the display file, drawing each component
line in turn
 The display program has commands for point, line, and
character plotting
 The display processor sends digital and point coordinate
values to a vector generator

ARCHITECTURE OF CALLIGRAPHIC DISPLAY

 The vector generator converts the digital coordinate
values to analog voltages for the beam-deflection
circuits
 The beam-deflection circuits displace the electron
beam for writing on the CRT’s phosphor coating
 Recommended refresh rate is 40 –50 Hz.
 Scope of animation– mixture of static and dynamic
parts of a picture

DRAWBACK
 Random scan displays are designed for line
drawing applications and cannot display realistic
shaded scenes
 Since picture definition is stored as a Set of line-
drawing instructions and not as a set of intensity
values for all screen points

SOME TERMS
 Phosphor’s Fluorescence is the light emitted as
electrons (unstable) lose their excess energy while
the phosphor is being struck by electrons
 Phosphorescence is the light given off by the return
of the relatively more stable excited electrons to their
unexcited state once the electron beam excitation is
removed
 Phosphor’s persistence is defined as the time from
the removal of excitation to the moment when
phosphorescence has decayed
 long persistence : several seconds or minutes
 short persistence :10-60 µs (common in modern displays)

RASTER SCAN DISPLAY
 Used in television screens, display monitors etc.
 Unlike DVST and random-scan which were line-drawing
devices, refresh CRT is a point-plotting device
 Refresh buffer (also called frame buffer) stores the
drawing primitives in terms of points and pixels
components
 The electron beam is swept across the screen one row
at a time from top to bottom. As it moves across each
row, the beam intensity is turned on and off to create a
pattern of illuminated spots. This scanning process is
called refreshing.
 Each complete scanning of a screen is normally called a
frame.

 The refreshing rate, called the frame rate, is
normally 60 to 80 frames per second, or described
as 60 Hz to 80 Hz.
 At the end of each scan line, the electron beam
returns to the left side of the screen to begin
displaying the next line (horizontal retrace).
 And at the end of each frame, the electron beam
returns to the top left corner of the screen to begin
the next frame (vertical retrace).
 Picture definition is stored in a memory area called
the frame buffer.
 This frame buffer stores the intensity values for all
the screen points.

 The quality of the raster image is determined by the
total number of pixels (resolution) and the amount
of information in each pixel (Color depth/ intensity)

ARCHITECTURE OF RASTER DISPLAY

BASIC VIDEO CONTROLLER REFRESH
OPERATION

RASTER SCAN DISPLAY
 Each screen point is called a pixel (picture element
or pel).
 Each point is an addressable point in screen and
memory
 Line cannot be drawn directly from one point to
another
 This causes the effect of ‘aliasing’, ‘jaggies’ or
‘staircase’ effect
 Refresh/Frame buffer is also called Bit-plane

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
a) General line b) Special cases

REFRESH RATE, VIDEO BASICS AND SCAN
CONVERSION
 Raster is stored as a matrix of pixels representing the
entire screen area
 Entire image is scanned out sequentially by the video
controller (one raster line at a time)
 The raster lines are scanned from top to bottom and
then back to the top
 The intensity of the beam decides the brightness of
the pixel
 At least one memory bit for each pixel (called bitmap
or bitplane)

COMMON TERMS
 Resolution: The maximum number of points that
can be displayed without overlap on a CRT is
referred to as the resolution.
 Aspect Ratio: Aspect ratio is a number which gives
the ratio of vertical points to horizontal points
necessary to produce equal length lines in both
directions on the screen.
Aspect ratio= width/ height
For example, if a graphic has an aspect ratio of 2:1,
it means that the width is twice as large as the height

 Bitmap or Bitplane: On a black and white system
with one bit per pixel, the frame buffer is commonly
known as a bitmap.
 Bandwidth of the display: The rate at which the
beam can be turned OFF to ON and vice-versa.
 For N pixels per scan line, it is necessary to turn the
electron gun at a maximum rate of N/2 times ON
and N/2 times OFF;
 This will create alternate black and white lines on
the screen.

COLOR DISPLAYS
 Discussed CRT can generate a single color at a
time.
 We can also generate multicolors using multilayer
phosphor.
 The electron beam penetrates this multilayer.
 Such a CRT is known as beam penetration CRT.
 There are two ways of getting colored displays:
 Beam penetration method
 Shadow mask method

COLOR DISPLAY- BEAM PENETRATION
METHOD
 It is a cheaper method and is used in vector or random
scan displays.
 In this method the inside section of CRT is coated with
red (outer layer) and green (inner layer) phosphors.
 If the electrons are slow they penetrate only the outer
layer thus emitting red light, and if the electrons are
moving fast they penetrate the outer layer and the inner
layer.
 The electrons speed is also adjusted in such a way that
by combination of red and green, orange and yellow
color are also produced.
 The limitation of this method is that only four colors can
be displayed in the screen.
 Since we have only four colors the quality of image is
diminished.

COLOR DISPLAY- SHADOW MASK METHOD
 It is used in raster scan display systems.
 Three electron guns instead of one inside the CRT, with
one electron gun for each primary color.
 The electron guns are frequently arranged in a triangular
pattern called delta corresponding to a similar
triangular pattern of red, green and blue phosphor dots
on the face of the CRT.
 These phosphors are capable of emitting red, green,
and blue light respectively
 A thin metal screen called a shadow mask is placed
between the phosphor coating and electron guns
 The tiny holes on the shadow mask constrain each
electron beam to hit its corresponding phosphor dots

BEAM PENETRATION METHOD V/S SHADOW
MASK METHOD
Beam Penetration
method
Shadow Mask method
Where Used It is used
with Random Scan
System to display
color.
It is Used With Raster Scan System to display color.
Colors It can displays Only
four colors i.e. Red ,
Green, Orange and
Yellow.
it can display Millions of colors.
Color Dependency Less colors are
available because the
colors in Beam
Penetration depends
on the speed of the
electron beam.
Millions of colors are available because the colors in Shadow
Mask depends on the type of the ray.
Cost It is Less
Expensive as
compared to Shadow
Mask.
It is More Expensive than other methods.
Picture Quality Quality of picture is
not so good i.e. Poor
with Beam Penetration
Method.
Shadow Mask gives realism in picture with shadow effect and millions of
color.
Resolution It gives High
Resolution.
It gives Low Resolution.
Criteria In Beam Penetration
method, Color display
depends on how far
electron excites outer
Red layer and then
Green layer.
In Shadow Mask Method, there are no such criteria for producing colors. It is
used in computers, in color TV etc.

FRAME BUFFER
 Frame buffer or refresh buffer in raster scan displays is
a memory storage area that holds the intensity values of
all screen positions (pixel).
 Frame buffer requires only a single bit per pixel, the
amount of memory is called bitmap or bitplane.
 Frame buffer requires several megabytes of storage
called pixmap.

N- BIT PLANE GRAY LEVEL FRAME BUFFER
 Choice of the number of gray scales and colors
depend on the value of N (bit plane size)
N = 1 –two colors (B&W)
N = 3 –8 gray scales or colors
N = 8 –256 gray scales or colors
N = 24 –16 million colors
 A DAC (digital-to-analog converter) is used to
convert the bit value (0, 1) to analog signals for
refreshing the screen

A SINGLE BIT PLANE BLACK & WHITE
FRAMEBUFFER

AN N-BIT PLANE GRAY LEVEL FRAME
BUFFER

REFRESH RATE, VIDEO BASICS AND SCAN
CONVERSION
A typical example:
 If one uses a 512x512 element raster display,
memory size required in case of single bitplane
frame buffer?
32 KB
 Memory size required for N-bit plane gray level
frame buffers:
 If N=3 memory size required?
96KB

 In case of one-bit for each color frame buffer, we
get 8 colors as:

FULL COLOR FRAME BUFFER
 Typically 8-bit planes per color is used, which gives
24-bit plane frame buffer.
 Each group of bit-planes drives an 8-bit DAC.
 Each group generates 256 shades of intensities of
red, green or blue.
 Hence we obtain 2^24= 1,67,77,216 possible
colors.
 This is called a full color frame buffer.

COLOR MODELS
 “Color model is a 3D color coordinate system to produce all
range of color through the primary color set.” There are
millions of colors used in computer graphics. The light
displays the color. A Color model is a hierarchical system in
which we can create every color by using RGB (Red, Green,
Blue) and CMYK (Cyan, Magenta, Yellow, Black) models. We
can use different colors for various purposes.
 The total number of colors displayed by the monitor depends
on the storage capacity of the video controller card.
 The Video controller card is used as an interface between the
computer system and the display device. It is also known as
“Video Random Access Memory (VRAM).”

 Additive Color Model: It is also named as “RGB
model.” RGB stands for Red, Green, Blue. The
Additive color model uses a mixture of light to
display colors. The perceived color depends on the
transmission of light. It is used in digital media.
 For Example– Computer Monitor, Television etc.

 Subtractive Color Model: It is also named as
“CMYK Model.” CMYK stands for Cyan, Magenta,
Yellow, and Black. The Subtractive model uses a
reflection of light to display the colors. The
perceived color depends on the reflection of light.
 The CMYK model uses printing inks.
 For Example– Paint, Pigments, and color filter etc.

Advantages:
 Easy to Implement.
 It uses color space for applications.
 No transformation for data display.
Disadvantages:
 We cannot transfer the color values from one to
another device.
 Complex to determine the particular color.

QUESTIONS
 1) Find out the time required to scan one row of
screen if the screen resolution is 20MP(mega
pixel) , aspect ratio 5/4 and refresh frequency is
30Hz).
 2) How much time is spent scanning across each
row of pixels during screen refresh on a raster
system with resolution of 1280 X 1024 and a
refresh rate of 60 frames per second?

QUESTIONS
 3) Consider three different raster systems with
resolutions of 640 x 480, 1280 x 1024, and 2560 x
2048.
a) What is the size of frame buffer (in bytes) for each
of these systems to store 12 bits per pixel?
b) How much storage (in bytes) is required for each
system if 24 bits per pixel are to be stored?
 4) Find out the aspect ratio of the raster system
using 8 x 10 inches screen and 100 pixel/inch.

QUESTIONS
 5) Consider two raster systems with the resolutions
of 640 x 480 and 1280 x 1024.
a) How many pixels could be accessed per second
in each of these systems by a display controller
that refreshes the screen at a rate of 60 frames
per second?
b) What is the access time per pixel in each system?

 6) Suppose raster system is to be designed using
on 8 inch X 10 inch screen with a resolution of 100
pixels per inch in each direction. If we want to store
6 bits per pixel in the frame buffer, how much
storage (in bytes) do we need for frame buffer?
Calculate Aspect ratio also.
 7) Consider a raster system with the resolution of
1024 x 768 pixels and the color palette calls for
65,536 colors. What is the minimum amount of
video RAM that the computer must have to support
the above-mentioned resolution and number of
colors?

8) Compute the following:
(a) Size of 800 x 600 inch image at 240 pixels per
inch.
(b)Height of the resized image 1024 x 768 to one
that is 640 pixels wide with the same aspect ratio.
(c)Width of an image having height of 5 inches and
an aspect ratio 1.5

 9) Find out the size of frame buffer in MB if the
screen resolution is 12MP (mega pixel), aspect
ratio 3/4 and number of color combination required
12345.(RGB all are having equal no. of Frame
buffer).
 10) Find the number of colors a frame buffer of 8 bit
planes each red, green and blue, and 10 bits wide
lookup table can produce.
 11) Find the amount of memory required by an 8
plane frame buffer each of red, green and blue,
having 1024x 768 resolution.

 12) Find the refresh rate of a 512 x 512 frame
buffer, if the access time for each pixel is 200
nanoseconds(ns).
 13) Find the amount of memory required by a 3
plane frame buffer each of red, green and blue,
having 800 x600 resolution
 14) Find the refresh rate of a 1024 x 1024 frame
buffer, if it can access 32 pixels in a group
simultaneously, in an access time of 200 ns.

 15) In a 600*400 screen, how many KB does a
frame buffer need?
 16) A laser printer is capable of printing two pages
of size 9*11 inch/sec at a resolution of 600
pixels/inch. How many bits per second does such a
device requires?
 17) Suppose we have a computer with 32 bits per
word and a transfer rate of 1 MIPs. How long would
it take to fill a frame buffer of a 300 DPI (dots per
inch) laser printer with a page size of 8.5 inches by
11 inches?

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