The document provides an overview of computer graphics systems and their components. It discusses: 1) The four major applications of computer graphics: display of information, design, simulation and animation, and user interfaces. 2) The basic components of a graphics system including input devices, CPU, GPU, memory, frame buffer, and output devices. 3) Key graphics concepts such as pixels, resolution, color depth, and rasterization. 4) Examples of input devices like keyboards, mice, and tablets and their logical representation in programs.

1. Graphics System Basics & Models
Book:
Chapter 1 [Ed. Angel, Interactive Computer Graphics]

2. Computer Graphics
 Computer Graphics: Use of computer in generating
images.
 Computer graphics: concerned with all aspects of
producing pictures or images using a computer.

3. Applications of Computer Graphics
 Can be roughly divided into four major areas
 Display of Information
 Design
 Simulation and Animation
 User Interfaces

4. 1. Display of Information
 Classic graphics techniques
used as a medium of
conveying information
 Human written/spoken
language
 Historical era:
 Babylonians used to display
floor plans on stones
 Greeks used to display their
architectural plans and language
 Today graphical
representation are generated
by Architects, Designers using
computers.

5. Display of Information (Contd…)
 Statisticians
 Uses CG to display plots/graphs
of a data set
 Extract information from these
plots
 Very useful in extracting info from
large datasets.
 Medical Imaging
 Graphics used in Computed
Tomography (CT)
 Medical Resonance Imaging
(MRI)
 Ultrasound
 Data Visualization
 Understanding data by placing it
in visual context

6. 2. Design
 Many fields concerned
with design. (Engineering
& Arch)
 With set of specification, a
cost effective and esthetic
design is tried to achieve
using computer graphics.
 Starting 40 years ago,
today Computer Aided
Design (CAD) pervades
many fields.

7. 3. Simulation and Animation
 Simulation is the imitation of the
operation of a real-world process or
system over time.
 Flight simulators - train pilots.
 Safety and Cost reduction
 Architectural designs are tested in many
weather conditions
 Animation - illusion of motion
 Became famous: After successful
simulations
 Artistic effects are achieved.
 Complete movies are made using CG
 Photo-realistic images
 Virtual Reality-replicates an
environment that simulates physical
presence in places in the real world or
imagined worlds and lets the user
interact in that world.

8. 3. Simulation & Animation (Virtual Reality)

9. 4. User Interfaces
 Interaction with computers
increased.
 Desktops, Tablets, Smartphones.
 Use of GUI has overcome CLI
 Microsoft Windows, Mac OS, Linux
 Android, iOS,
 Internet usage increased
 Webpages, applications all are
graphical
 Resources are accessed through
graphical browsers.
 Interaction with UI is so often, that
we have almost forgot that we’re
working with computer graphics.

10. A Graphics System
 General view of a graphics system
 Generally contains,
1. Input Devices
2. CPU
3. GPU (Graphics Processing Unit)
4. Memory
5. Frame Buffer
6. Output Devices

11. Pixels, Frame Buffer & Basic Terms
 Pixel: Short for Picture element
 The smallest addressable element of a
display device.
 Basic unit of a digital image.
 Each pixel corresponds to a location or
small area in the image.
 Raster: Array of picture elements or
pixels
 Images seen on displays are raters
produced by graphics sys.
 A raster is a grid of x and y coordinates on
a display space.

12. Pixels, Frame Buffer & Basic Terms (Contd…)
 Frame Buffer: portion of memory where pixels are
stored
 Core element of graphics system.
 Contains bitmap that is driven to video display
 Resolution: No. of pixels in frame buffer
 Resolution determines the details that can be seen in image
 Higher the resolution  Sharpen the image
 Depth / Precision: No. of bits used per pixel to
determine its properties like color
 1-bit-deep frame buffer  allows only two colors
 8-bit-deep frame buffer  allows 28 (256) colors.
 16-bit (High color)  216 Colors
 24-bit (True color)  224 Colors

13.  In Simple Sys: Frame Buffer only hold colored pixels that
are displayed
 In most systems, The frame buffer holds far more
information,
 depth information needed for creating images from 3D data.
 In these systems, the frame buffer comprises multiple
buffers,
 one or more of which are color buffers that hold the colored
pixels that are displayed.
 Terms, frame buffer and color buffer can be used
synonymously.
Pixels, Frame Buffer & Basic Terms (Contd…)

14. CPU and GPU
 In simple system there may be only one CPU
 In early systems, frame buffer was the part of standard
memory
 CPU is responsible for both Normal and Graphical
Processing
 Main graphical processing of CPU is
 Take graphical primitives from application program
 Like (lines, polygons, circles)
 Assign values to the pixels in frame buffer that best
represent those entities.
 Rasterization: Conversion of geometrical entities to
pixel colors and locations in frame buffer. (a.k.a scan

15. CPU & GPU (Contd…)
 Today, all graphics system are characterized by
special purpose graphics processing unit (GPU).
 GPU: A processing unit custom-tailored to carry out
specific graphics functions
 GPU can either be on the same system board or on
separate graphics card
 Frame buffer usually resides on the same board as GPU
 Frame buffer is accessed through GPU

16. Output Devices
 Cathode Ray Tube (CRT)
 Most dominant type of display (until, recently)
 Basic Op: When electron strikes the phosphor coating,
light is emitted.
 Deflection plates: to control the direction of the beam
 Computer output is converted from digital(bits) to
analog(voltage) by converters across x and y deflection
plates.
 When sufficiently intense beam of electrons is directed at
the phosphor, light appears on CRT surface

17. Output Devices (Contd…)
 Refresh rate: No. of times per second the device
retrace the same path/image.
 CRT emits light for short time (few milli seconds)
 To see flickering-free image, same image must be retraced.
 Old systems: Refresh rate = frequency of power system
 50 Hz in US and 60 Hz in most of the world
 Raster System (Fundamental ways of displaying
pixels)
 Non-interlaced: Pixels are displayed row by row at refresh
rate
 Interlaced Display: Odd and even rows are refreshed,
alternatively. 30 Hz instead of 60 Hz.

18. Output Devices (Contd…)
 Colored CRTs
 Phosphors of three different colors (Red,
Green, Blue)
 Phosphors arranged in small groups.
 Phosphors in triangular groups are called
triads
 Have three electron beams.
 Shadow Mask: a metal sheet with small
holes
 Used to ensure the excitation of proper color
phosphor.

19. Output Devices (Contd…)
 Flat-panel Technology.
 Flat-panels are inherently raster based.
 Mostly used flat panels are LCD, LED and Plasma
 Generic flat-panel display have
 2-outside plate: containing parallel
grids of wires, oriented
perpendicular to each other.
 Middle plate contains different
material depending upon the
technology.

20. Output Devices (Contd…)
 Flat-panel Display
 By sending electrical signal to proper wire on both plates.
 Electric field is produced at the point of intersection of two
wires
 Electric field is used to control the corresponding element on
the middle plate.
 Electric field produced can be used in,
 LED, to turn corresponding led on or off
 LCD, to control polarization of liquid crystals to pass light
 Plasma, to energize gases in order to glow or not.

21. Input Devices
 Input Devices: Devices used for input purposes.
 Common input device Keyboard, mouse
 Other input devices include joy stick, track ball, space ball
 Input Devices (Perspective)
 Physical Device
 Logical Device (application / programmer perspective)
 Their properties are specified in terms of “what they do” from
application perspective.
 For example: cout in C++ outputs the string, the output device
could be printer, display/terminal or a disk file.
 Even the “cout” output could be input for another program.

22. Input Devices (Physical)
 Two primary types of Input Devices
 Keyboard Devices
 Pointing Devices
 Keyboard generally include physical keyboards or
devices that return character codes.
 ASCII code is used to represent characters.
 ASCII assigns a single unsigned byte to each character.
 Internet application use multiple bytes to represent each
char.
 Mouse & Trackball:
 A mechanical mouse and trackball works on same
principal.
 Motion of the ball is converted to signals by converters.

23. Input Devices (Physical)
 Signals from encoders might be interpreted as
position (Not necessarily)
 Driver/Program can interpret the signals as two
velocities.
 The Computer can integrate velocities to obtain
position.
 When ball rotates position
changes, otherwise not.
 In this mode, positioning is
relative.
 Motion sensing devices are known as Relative
positioning devices

24. Input Devices (Physical)
 Data Tablets:
 Absolute positioning
 Position is determined using electromagnetic
interactions between signals traveling through the
wires and sensors in the stylus
 Position sensing devices are known as absolute
positioning devices
 READING: Space ball and Joy stick

25. Input Devices (Logical)
 Logical Input Devices:
 Addressing of physical input devices as abstract data
types
 ADT: data type defined by its behavior from user view
 Two major characteristics describe logical
behavior of input device:
1. The measurements that the device returns to the
user program
2. The time when the device returns those
measurements.

26. Input Devices (Logical)
 Logical Input Devices:
 String: Return string of characters from Keyboard, File,
etc
 Locator: Returns a position (in x, y coordinates)
 Pick: Returns a segment name & pick identifier of object
pointed by the user.
 Choice: Represents a choice from a selection of several
possibilities.
 Valuator: Returns a real/analogue value, for example, to
control some sort of analogue device.
 Stroke: series of locations. (Tablets/Touch inputs)

27. Input Modes
 Input is provided in terms of two entities
 Measure: The returned data from input devices.
 Ex: Data stream from keyboard OR location of pointer from
mouse
 Trigger: Physical input to signal the computer.
 Ex: Pressing of Return (Enter) Key / Esc Key OR clicking the
mouse button.
 Measure of device can be obtained in three (03)
distinct modes
 Each mode is defined by: Relationship b/w measure &
trigger.

28. Request Mode – Input Modes
 The measure of the device is not returned to the
program until the device is triggered.
 Ex: cin / scanf in C++/C language. (Input Statements)
 Program waits for trigger when input statement is
encountered.
 Take as long as the user wants.
 The measure is only returned upon trigger. (e.g upon
pressing enter/return)

29. Sample Mode (Input Modes)
 Sample-Mode: Input is immediate. Measure is
returned as the function is encountered in App.
 Position the device or Enter data before the function call.
 Program retrieves “measure” immediately from the
buffer/file/location.
 For example, your application can obtain the location
of the screen cursor at any point in time, through the
use of SAMPLE mode input.

30. Event Mode – Input Modes
 Case: Multi input devices each with its own measure &
trigger.
 For Example: Flight simulators with multiple inputs.
 Event Mode:
 Application Program & Devices work independently of each other.
 Each time listed device is triggered: measure + id is stored in event
queue
 App. Prog. Retrieves input from event queue whenever required.
 Event Mode (Callback Approach):
 Associate a function call (callback) with events specifically.
 OS queries event queue and calls the associated function.
 Efficient approach in client-server scenarios.

31. Images – Physically & Synthetic
Elements of Image Formation
 Basic entities of Image Formation
 Objects
 Viewers
 Light

32. Object(s)
 The object exists in space independent of any
image-formation process and of any viewer.
 Computer Graphics: deals with synthetic objects
 Objects are formed by specifying positions of
geometric primitives(basic shapes) in space like
triangle, polygons etc
 Mostly, set of spatial positions (vertices) are used to
define objects
 For Ex: line can be defined by two vertices
 Triangle can be defined by three vertices.

33. Viewer(s)
 To form an image, there must be someone or
something that is viewing our objects. Like human, a
camera, etc.
 It is the viewer that forms the image of our objects.
 Human Visual System: Image is formed at back of eye
 Camera: Image is formed in the film plane
 Objects are usually seen from different perspectives.

34. Light
 Be it physical or synthetic images are in complete
without light.
 No light = dark objects = no image formation
 Light is electromagnetic radiation.
 Light Spectrum: Radio + Infrared + Visual spectrum
 Visual spectrum: 350 – 780 nm
 Around 520 nm: Green
 Near 450 nm: Blue
 Near 650 nm: Red
 Except from recognizing that which frequency
is for which color CG doesn’t deal with light

35. Light Spectrum

36. Imaging Systems
 Physical imaging systems to understand imaging in
computers.
 Pin-hole Camera
 Human Visual System
 Pin-hole: To understand basic working principles of
camera.
 Human visual system is complex but obeys the
physical principles of other imaging systems

37. Pin-hole Camera
 A pinhole camera is a box with a small hole in the
center of one side of the box
 film is on the side opposite the pinhole.
 Hole is so small that only a single ray of light can
enter (assumption)
 For Example: We have point in scene (x, y, z)
 At Image: z = -d
 y = yp
 x = xp (In top view)
 (xp, yp, -d) is called
projection of (x,y,z)

38. Pin-hole Camera
 Color: In idealized mode, color of the image will be
same as in scene
 Field/Angle of View: is the extent of the observable
world that is seen at any given moment.
 If h is the height of camera (film) then
 Angle is formulated using basic
Trigonometry.

39. Pin-hole Camera
 Depth of Field: Every object in angle of view is in
focus i.e appears sharply.
 In Ideal pinhole camera depth of field is infinite.
(Assumed)
 Disadvantages of Pinhole camera
 It admits only single ray – almost no light.
 Camera cannot be adjusted to have different angle of
view.
 By replacing hole with lens; problems can be
eliminated
 With proper lens more light can be entered (larger
aperture)

40. Human Visual System
 Human Visual System is extremely complex.
 Light enters through cornea and lens
 Iris opens/shuts to adjust the amount of light
 Image is formed at retina (back of the eye)
 Cells (Rods and Cones) are sensors
 They excites/responds when light enters eye (350-780
nm)
 Rods: 1 type; Low light sensors; Night vision, not color
sensitive
 Cones: 3 types; responsible for color vision
 Resolution of Visual System
 Resolution: Measure of what size objects can we see.
 Technically: it is a measure of how close we can place

41. Human Visual System
 Brightness: Brightness is an overall measure of how
we react to the intensity of light
 HVS reacts differently to different wavelengths of light
 HVS is more sensitive to green and less sensitive to red &
blue
 HVS only reacts to three colors instead of whole
visual spectrum due to three types of cones.
 These colors are called primary colors.
 Primary colors are Red, Blue and Green.

42. Synthetic Camera Model
 The paradigm of emulating image formation by
optical system in computer is known as Synthetic
Camera Model
 Basic Principles:
 As Object & Viewer are independent of each, so CG (API)
should have separate functions for specifications.
 Images can be computed using simple geometric
calculation like in pin hole camera.

43. Synthetic Camera Model
 In pin hole camera image formed is
flipped.
 In computer, image is retain; by
moving the plane to front (Virtual
image plane)
 A line is drawn called projector from
center of lens/projection (COP) to
the object/point.
 All the light originates from COP
 This virtual image plane is called
projection plane

44. Synthetic Camera Model
 There is always limitation to the size of the image. In optical
system; field of view expresses the limitation
 Synthetic Camera Model places a Window/Rectangle in
projection plane to cope with the limitation.
 This window / rectangle through which a viewer at COP sees the
world called Clipping window/rectangle
 Given the following
 Location of COP
 Orientation of Projection plane
 Size of clipping window
 We can determine that which
objects will appear in image

45. Programmer’s Interface
 User interact with graphics system in different ways
like using CAD modules, paint programs etc.
 Programmers interact with GS using graphics library
(API)
 Graphics API: Interface b/w programmer and Graphics
system specified through set of functions.
 Programmers don’t see h/w related details.
 Software Drivers interpret the output of API to the
form that is understood by the specific hardware.

46. Three Dimensional API
 As per synthetic camera model, 3D API must provide
functions to specify,
 Objects
 Viewer
 Light Sources
 Material properties.
 Objects are specified using vertices.
 Objects are usually specified using geometric
primitives like lines, polygons, triangles etc
 Complex objects may involve multiple ways of
specification.

47. Three Dimensional API
 Camera can be defined in variety of ways.
 APIs differ in camera selection and methods
 Four types of specification for Camera
 Position: Camera location (COP)
 Orientation: Rotation of camera in axes.
 Focal length: Size of the image/ Angle of view
 Film plane: height & width
 Specifications can be satisfied in various ways
 Most used way is coordinate system transformation
 Transformations convert object positions
represented in coordinate system.

48. Three Dimensional API
 Light Sources
 Light sources are specified by their
 location, strength, color and direction
 These properties are specified for each light sources
used.
 Material Properties:
 Characteristics or attributes of the objects
 These attributes are specified when the objects are
defined
 Both light and material properties depend upon the
light-material model API supports.

49. The Modeling–Rendering Paradigm
 Model: Mathematical/Geometrical description of
shapes
 Rendering: Process of generating images from
models
 Modeling can be separated from Rendering.
 Helpful in generating complex images.
 The file/data produced by the modeler is used by the
Renderer.
 This File could be simple; containing info in specific
format

50. The Modeling–Rendering Paradigm
 Different hardware and software at both blocks.
 Modeler, as well as Rendered are both
customizable
 Use diff: modeler with same renderer
 Use same modeler with diff: renderer
 Most popular approach now a days.
 Models, lights, camera etc are place in special data
structure called scene graph
 Scene graph is then passed to renderer or game
engine.

51. Graphics Architectures
 Early graphics system: general-purpose computer of
von Neumann architecture
 Single processor system (Single instruction
Execution)
 Calligraphic CRT display
 Generate a line segment by connecting two points.
 Host used to Run app & compute end points and
send them to CRT
 Info needs to be sent at high speed (to avoid flicker)
 Refreshing was slow that even small image
would burden expensive computer.

52. Display Processors
 Earliest special purpose graphics system
 To separate the process of continuous display of
refreshing
 Display processor included instruction to display
CRT primitives
 Host generate image (Using instructions)
 Send to Display processor
 Display processor store program in memory
(as display file / display list)
 Display processor runs
program iteratively

53. Pipeline Architecture
 Process/Operation divided into several independent /
dependent segments.
 a + (b ∗ c)
 Pipelining increases throughput of the computer.

54. Graphics Pipeline
 Sets of Object  Objects (Set of primitives) 
vertices
 Complex objects may contain millions of vertices
 To make process of imaging fast we use pipeline
 Graphical pipeline consists of
 Vertex Processing
 Clipping and Primitive Assembly
 Rasterization
 Fragment Processing

55. 1. Vertex Processing
 Two major functions of this block
 Coordinate transformation
 Compute color of each vertex

56. Clipping and Primitive Assembly
 Vertices are assembled into primitives (shapes)
 No camera can see the whole world
 Clipping must be done.
 Clipping window/volume is considered
 Clipping is done primitive by primitive.
 Output: set of primitives which will appear in clipping
image.