Computer Graphics Viva Questions

MC1704 Computer Graphics and Multimedia System

2 Marks Questions

1. What is scan conversion?
A major task of the display processor is digitizing a picture definition
given in an application program into a set of pixel-intensity values for storage in
the frame buffer. This digitization process is called scan conversion.

2. Write the properties of video display devices?
Properties of video display devices are persistence, resolution, and aspect
ratio.
3. What is rasterization?
The process of determining the appropriate pixels for representing picture
or graphics object is known as rasterization.

4. Define Computer graphics.
Computer graphics remains one of the most existing and rapidly growing
computer fields. Computer graphics may be defined as a pictorial representation
or graphical representation of objects in a computer.

5. Name any four input devices.
Four input devices are keyboard, mouse, image scanners, and trackball.

6. Write the two techniques for producing color displays with a CRT?
Beam penetration method, shadow mask method

7. What is vertical retrace of the electron beam?
In raster scan display, at the end of one frame, the electron beam returns to the
left top corner of the screen to start the next frame, is called vertical retrace of the
electron beam.

8. Short notes on video controller?
Video controller is used to control the operation of the display device. A fixed
area of the system is reserved for the frame buffer, and the video controller is
given direct access to the frame buffer memory.

9. What is bitmap?
Some system has only one bit per pixel; the frame buffer is often referred to as
bitmap.

10. Differentiate plasma panel display and thin film electro luminescent display?
In plasma panel display, the region between two glass plates is filled with
neon gas. In thin film electro luminescent display, the region between two glasses
plates are filled with phosphor, such as zinc sulphide doped with manganese.

11. What is resolution?
The maximum number of points that can be displayed without overlap on
a CRT is referred to as the resolution.

12. What is horizontal retrace of the electron beam?
In raster scan display, the electron beam return to the left of the screen after
refreshing each scan line, is called horizontal retrace of the electron beam.

13. What is filament?
In the CRT, heat is applied to the cathode by directing a current through a
coil of wire, is called filament.

14. What is pixmap?
Some system has multiple bits per pixel, the frame buffer is often referred
to as pixmap.

15. Write the types of clipping?
Point clipping, line clipping, area clipping, text clipping and curve
clipping.

16. What is meant by scan code?
When a key is pressed on the keyboard, the keyboard controller places a
code carry to the key pressed into a part of the memory called as the keyboard
buffer. This code is called as the scan code.

17. List out the merits and demerits of Penetration techniques?
The merits and demerits of the Penetration techniques are as follows
• It is an inexpensive technique
• It has only four colors
• The quality of the picture is not good when it is compared to other
techniques
• It can display color scans in monitors
• Poor limitation etc.

18. List out the merits and demerits of DVST?
The merits and demerits of direct view storage tubes [DVST] are as follows
• It has a flat screen
• Refreshing of screen is not required
• Selective or part erasing of screen is not possible
• It has poor contrast
Performance is inferior to the refresh CRT.



19. What do you mean by emissive and non-emissive displays?
The emissive display converts electrical energy into light energy. The plasma
panels, thin film electro-luminescent displays are the examples.
The Non-emissive are optical effects to convert the sunlight or light from any
other source to graphic form. Liquid crystal display is an example.

20. List out the merits and demerits of Plasma panel display?
Merits
• Refreshing is not required
• Produce a very steady image free of Flicker
• Less bulky than a CRT.
Demerits
• Poor resolution of up to 60 d.p.i
• It requires complex addressing and wiring
• It is costlier than CRT.

21. What is persistence?
The time it takes the emitted light from the screen to decay one tenth of its
original intensity is called as persistence.

22. What is Aspect ratio?
The ratio of vertical points to the horizontal points necessary to produce
length of lines in both directions of the screen is called the Aspect ratio. Usually
the aspect ratio is ¾.

23. What is the difference between impact and non-impact printers?
Impact printer press formed character faces against an inked ribbon on to
the paper. A line printer and dot-matrix printer are examples.
Non-impact printer and plotters use Laser techniques, inkjet sprays,
Xerographic process, electrostatic methods and electro thermal methods to get
images onto the papers. Examples are: Inkjet/Laser printers.

24. Define pixel?
Pixel is shortened forms of picture element. Each screen point is referred to as
pixel or pel.

25. What is frame buffer?
Picture definition is stored in a memory area called frame buffer or refresh
buffer.

26. Where the video controller is used?
A special purpose processor, which is used to control the operation of the
display device, is known as video controller or display controller.


27. What is run length encoding?
Run length encoding is a compression technique used to store the intensity
values in the frame buffer, which stores each scan line as a set of integer pairs.
One number each pair indicates an intensity value, and second number specifies
the number of adjacent pixels on the scan line that are to have that intensity value.

28. What is point in the computer graphics system?
The point is a most basic graphical element & is completely defined by a
pair of user coordinates (x, y).

29. Write short notes on lines?
A line is of infinite extent can be defined by an angle of slope θ and one
point on the line P=P(x,y). This can also be defined as y=mx+C where C is the Y-
intercept.

30. Define Circle?
Circle is defined by its center xc, yc and its radius in user coordinate units.
The equation of the circle is (x-x
c
) + (y-y
c
) = r
2
.

31. What are the various attributes of a line?
The line type, width and color are the attributes of the line. The line type
include solid line, dashed lines, and dotted lines.

32. What is antialiasing?
The process of adjusting intensities of the pixels along the line to
minimize the effect of aliasing is called antialiasing.

33. What is Transformation?
Transformation is the process of introducing changes in the shape size and
orientation of the object using scaling rotation reflection shearing & translation
etc.

34. What is translation?
Translation is the process of changing the position of an object in a
straight-line path from one coordinate location to another. Every point (x , y) in
the object must under go a displacement to (x
|
,y
|
). the transformation is:
x
|
= x + tx ; y
|
= y+ty

35. What is rotation?
A 2-D rotation is done by repositioning the coordinates along a circular
path, in the x-y plane by making an angle with the axes. The transformation is
given by: X
|
= r cos (θ + φ) and Y
|
= r sin (θ + φ).

36. What is scaling?
A 2-D rotation is done by repositioning the coordinates along a circular
path, in the x-y plane by making an angle with the axes. The transformation is
given by: X
|
= r cos (θ + φ) and Y
|
= r sin (θ + φ).

37. What is shearing?
The shearing transformation actually slants the object along the X
direction or the Y direction as required. ie; this transformation slants the shape of
an object along a required plane.

38. What is reflection?
The reflection is actually the transformation that produces a mirror image
of an object. For this use some angles and lines of reflection.

39. What are the two classifications of shear transformation?
X shear, y shear.

40. A point (4,3) is rotated counterclockwise by an angle of 45°. Find the rotation
matrix and the resultant point.

41. Name any three font editing tools.
ResEdit, FONTographer,

42. Differentiate serif and sans serif fonts. Give one example
Serif fonts has a little decoration at the end of the letter, but serif font has
not. Times, new century schoolbook is the examples of serif fonts. Arial, potima
are examples for sans serif fonts.

43. Distinguish between window port & view port?
A portion of a picture that is to be displayed by a window is known as
window port. The display area of the part selected or the form in which the
selected part is viewed is known as view port.

44. Define clipping?
Clipping is the method of cutting a graphics display to neatly fit a predefined
graphics region or the view port

45. What is the need of homogeneous coordinates?
To perform more than one transformation at a time, use homogeneous
coordinates or matrixes. They reduce unwanted calculations intermediate steps
saves time and memory and produce a sequence of transformations.

46. Distinguish between uniform scaling and differential scaling?
When the scaling factors sx and sy are assigned to the same value, a uniform
scaling is produced that maintains relative object proportions. Unequal values for
sx and sy result in a differential scaling that is often used in design application


47. What is fixed point scaling?
The location of a scaled object can be controlled by a position called the
fixed point that is to remain unchanged after the scaling transformation.

48. What is Bezier Basis Function?
Bezier Basis functions are a set of polynomials, which can be used instead
of the primitive polynomial basis, and have some useful properties for interactive
curve design.

49. What is surface patch
A single surface element can be defined as the surface traced out as two
parameters (u, v) take all possible values between 0 and 1 in a two-parameter
representation. Such a single surface element is known as a surface patch.

50. Define B-Spline curve?
A B-Spline curve is a set of piecewise(usually cubic) polynomial segments that
pass close to a set of control points. However the curve does not pass through these
control points, it only passes close to them.

51. What is a spline?
To produce a smooth curve through a designed set of points, a flexible strip called
spline is used. Such a spline curve can be mathematically described with a piecewise
cubic polynomial function whose first and second derivatives are continuous across
various curve section.

52. What are the different ways of specifying spline curve?
• Using a set of boundary conditions that are imposed on the spline.
• Using the state matrix that characteristics the spline
• Using a set of blending functions that calculate the positions along the
curve path by specifying combination of geometric constraints on the
curve

53. What are the important properties of Bezier Curve?
• It needs only four control points
• It always passes through the first and last control points
• The curve lies entirely within the convex half formed by four control
points.

54. Define Projection?
The process of displaying 3D into a 2D display unit is known as
projection. The projection transforms 3D objects into a 2D projection plane

55. What are the steps involved in 3D transformation?
• Modeling Transformation
• Viewing Transformation
• Projection Transformation
Workstation Transformation

56. What do you mean by view plane?
A view plane is nothing but the film plane in camera which is positioned
and oriented for a particular shot of the scene.

57. Define projection?
The process of converting the description of objects from world
coordinates to viewing coordinates is known as projection

58. What you mean by parallel projection?
Parallel projection is one in which z coordinates is discarded and parallel
lines from each vertex on the object are extended until they intersect the view
plane.

59. What do you mean by Perspective projection?
Perspective projection is one in which the lines of projection are not
parallel. Instead, they all converge at a single point called the center of projection.

60. What is Projection reference point?
In Perspective projection, the lines of projection are not parallel. Instead,
they all converge at a single point called Projection reference point.

61. Define computer graphics animation?
Computer graphics animation is the use of computer graphics equipment
where the graphics output presentation dynamically changes in real time. This is
often also called real time animation.

62. What is tweening?
It is the process, which is applicable to animation objects defined by a
sequence of points, and that change shape from frame to frame.

63. Define frame?
One of the shape photographs that a film or video is made of is known as
frame.

64. What is key frame?
One of the shape photographs that a film or video is made of the shape of
an object is known initially and for a small no of other frames called keyframe

65. Define Multimedia
Multimedia is the use of the computer to present and combine text,
graphics, audio and video with links and tools that lets the user to navigate,
interact, create and communicate.
66. What is multimedia PC:
A multimedia PC is a computer that has a CD-ROM or DVD drive and
supports 8-bit and 16-bit waveform audio recording and playback, MIDI sound
synthesis, and MPEG movie watching, with a central processor fast enough and a
RAM large enough to enable the user to play and interact with these media in real
time, and with a hard disk large enough to store multimedia works that the user
can create.

67. Where to use multimedia?
Multimedia improves information relation. Multimedia applications
includes the following:
Business
Schools
Home
Public place

68. List out the benefits of multimedia
Benefits of multimedia are
Training
Sales
Communications
Medicines

69. What is hypermedia?
A set of documents in which a given document can contain text, graphics
video and audio clips as well as embedded references to other documents world
wide web pages are hypermedia documents.

70. What is hypertext?
Hyper text is an application of indexing text to provide a rapid search of
specific text strings in one or more documents. Hypertext is an integral part of
hypermedia documents. In multimedia applications, a hypermedia documents is
the basic complex object of which text is a sub-object. Other sub-objects in the
basic object include images, sound, and full-motion video.

71. List out the building blocks of multimedia.
Text
Image
Sound
Animation
Video

72. What are the main functions of a multimedia development system?
Multimedia development system must perform main three functions as
follows:
Input data
Development
Data output
Data input from sources such as cameras or musical instruments,
application development, and data output to some delivery medium such as a
videodisk or CD-ROM.

73. Define Typeface
Typeface is measured in point sizes, where one point is approximately
1/72 of an inch. It is a measure of the height of the metal blocks containing letters.

74. Define the following:
(i) X-height (ii) Set (iii) Kerning
X-height: The X-height is the measurement of the height of the character
X, in other words of the middle bit without any ascender or descender.
(ii) Set: The width of the letters is called the set and is fixed relative to the
point-size.
(iii) Kerning: The spaces between letters in one world (tracking) can be
adjusted in a process called kerning.

75. Define the following respective to sound:
(i) Waveform (ii) Frequency (iii) Amplitude
i) Waveform
Sound is produced by the vibration of matter. During the vibration
pressure variation are created in the air surrounding it. The pattern of the
oscillation is called a waveform.
(ii) Frequency
The frequency of the sound is the reciprocal value of the period. It
represents the number of period s in a second and it is measured in Hertz
(Hz) or cycles per second.
(iii) Amplitude
A sound also has amplitude. The amplitude of a sound is a measure
of the displacement of the air pressure wave from its, or quiescent state.

76. Define quantization (or) resolution?
The resolution (or) quantization of a sample value depends on the number
of bits used in measuring the height of the waveform. An 8-bit quantization yields
256 possible values, 16-bit CD-qudra quantization results in over 65536 values.

77. What are the types of sound objects that can be used in multimedia production?
There are four types of sound objects that can be used in multimedia
production:
Waveform audio
MIDI sound tracks
Compact disc (CD) audio
MP3 files


78. What is MIDI?
Musical Instrument Digital Interface (MIDI) is the interface between
electronic musical instruments and computers is a small piece of equipment that
plugs directly into the computer’s serial port and allows the transmission of music
signal. MIDI is considered to be the most compact interface that allows full-scale
output.

79. List out the components of MIDI interface.
A MIDI interface has two different components:
Hardware
Data format
Hardware connects the equipment. It specifies the physical connection
between musical instruments, stimulate that a port MIDI port is built into an
instrument, specifies a MIDI cable and deals with electronic signals t that are sent
over the cable.
Data format encodes the information traveling through the hardware
MIDI data format includes an instrument –connected data format. The encoding
includes, besides the instrument specification, the notion of the beginning and end
of a note, basic frequency and sound volume; MIDI data allow an encoding of
about 10 octaves, which corresponds to 128 notes.

80. Define the term flicker in video.
A periodic fluctuation of brightness perception is called flicker effect.

81. Define Random scan/Raster scan displays?
Random scan is a method in which the display is made by the electronic beam
which is directed only to the points or part of the screen where the picture is to be
drawn.
The Raster scan system is a scanning technique in which the electrons sweep
from top to bottom and from left to right. The intensity is turned on or off to light and
unlight the pixel.

82. What is an MPC?
The MPC computer is not a hardware unit but rather a standard that includes
minimum specifications to turn Intel microprocessor-based computers into
multimedia computers.

83. List all the MPC standards
There are currently three MPC standards as follows
MPC Level 1
MPC Level 2
MPC Level 3
The standards apply not only to desktop computers but also to increasingly
more powerful multimedia laptops.


84. What is configuration of MPC level 1 standards?
The MPC level 1 minimum standard workstation consisted of a 16MHz
386SX microprocessor, atleast 2MB of RAM, a 30MB Hard disk, a CD-ROM
drive, VGA video (16 colors), an 8-bit audio board, speakers and/or headphones,
and Microsoft windows software with the Multimedia Extensions package.

85. Write the configuration of MPC level 2 standards.
MPC level 2 minimum standard consisted of a 25MHz 486SX
microprocessor with atleast 4MB of RAM, a 3.5-inch high density, a 160 MB or
larger hard disk drive, and a CD-ROM drive capable of sustained 300k per second
transfer rate with CD-DA outputs and volume control, 16-bit sound capability
with microphone input, and a color monitor with display resolution of atleast 640
X 480 with 65,536(64k) colors.

86. List out the input devices of multimedia.
Input devices for a multimedia system are as follows:
Keyboards
Mouse
Trackball
Touch screen
Magnetic card Encoders and Readers
Graphics Tablets
Scanners
Optical Character Recognition (OCR) devices
Voice Recognition Systems
Digital cameras

87. What is a Video disk?
Video disk serves as the output of motion pictures and audio. The data are
stored in an analog-coded format on the disk. The reproduced data meet the
highest quality requirements. Video disk has a diameter of approximately 30cm
and stores approximately 2.6 Giga bytes.

88. What is synchronization?
Integration of the different media is given through a close relation between
information units. This is called synchronization.

89. What is meant by Multimedia User Interface?
Multimedia user interface is a computer interface that communicates with
users multiple media.

90. Define the following terms:
(i) Compression Ratio (ii) Image Quality
(i) Compression Ratio: The Compression Ratio represents the size of the
original image divided by the size of the compressed image.
(ii) Image Quality: Compression ratio typically affects picture quality, the
higher the compression ratio, the lower the quality of the decompressed image.

91. What are the higher levels of multimedia communication system (MCS)?
The higher layers of the multimedia communication system are divided
into two architectural subsystems:
• Application subsystem
• Transport subsystem.

92. Define collaborative computing environment?
The recent infrastructure of networked workstations and pcs, and the
availability of audio and video at these end points, makes it easier to people to
cooperate and bridge space and time. In this way, network connectivity and
endpoint integration of multimedia provide users with a collaborative computing
environment. It is generally known as computer supported cooperative work
(CSCW).

93. List out the tools for collaborative computing
The tools used for collaborative computing are as follows:
• Electronic mail
• Bulletin boards(e.g. Usenet news)
• Screen sharing tools(e.g. show me from sunsoft)
• Text-based conferencing systems (e.g. Internet relay chat, CompuServe,
America online).
• Telephone conference systems.
• Conference rooms(e.g. video window from Bellcore)
• Video conference systems(e.g.,Mbone tools)

94. What is group communication (GC)?
Group communication (GC) involves the communication of multiple users
in a synchronous or an asynchronous mode with centralized or distributed control.

95. What are the consistent of a group communication?
Group communication architecture consists of the following:
• Support model
• System model
• Interface model
The GC support model includes group communication agents that
communicate via a multi-point multi-cast communication network.

96. Define the term Group Rendezvous?
Group rendezvous denotes a method, which allows one to organize
meetings and to get information about the group, ongoing meetings and other
static and dynamic information.

97. List out some examples for interface model protocols.
Synchronous rendezvous methods use:
• Directory services
• Explicit invitations
Directory services access information stored in a knowledge base about the
conference, such as the name of the conference, registered participants, authorized
users and name and role of the participants
98. What are the advantages and disadvantages of replicated architecture?
The advantages of replicated architecture are:
• Low network traffic
• Low response times
Low network traffic is because only input events are distributor among the
sites and low response times, since all participants get their output from local
copies of the application.
The disadvantages are the requirement of the same execution environment
for the application of each site, and the difficulty in maintaining consistency.

99. What are the advantages and disadvantages of centralized conference control?
The advantage of the centralized conference control is guaranteed
consistency of the conference state. The disadvantage is that when a new
participant (outside of the invited group) wants to join, explicit exchange of the
conference state must be performed among all participants, which causes large
delays.

100. What are the advantages of distributed conference control?
Advantages of distributed conference control are:
• Inherent fault tolerance-If a network connection breaks down in the
middle of a conference and it is repaired, it is easier to re-establish the
shared conference state since there is no strict consistency requirement.
• Scaling properties-At some point refresh periodicity needs to adapt to the
size and scope of the conference, otherwise, the conference may be in
danger of flooding itself with session reports.

101. What is a session manager?
Session management architecture is built around an entity session
manager, which separates the control from the transport. By creating a
reusable session manager, which is separated from the user interface,
conference oriented tools avoid a duplication of their effort.

102. List the various functionalities of session manager
Session manager includes local and remote functionalities. Local
functionalities include:
• Membership control management
• Floor control
• Media control management
• Configuration management
• Conference control management

103. What are the contents of synchronization?
Synchronization in multimedia systems comprises of content, spatial and
temporal relations between media objects.

104. What is presentation requirement?
Presentation requirements consist of intra-object synchronization, the
accuracy concerning delays in the presentation of LDUs and, for inter-object
synchronization, the accuracy in the parallel presentation of media objects.




Part- B (16 marks Questions)


1. Briefly explain about video display devices with necessary diagram? (16)
Video display devices: CRT, raster scan display, random scan display. (16)
Explain: CRT: basic design of CRT, electron gun-heated metal cathode,
control grid, focusing system.
raster scan display, random scan display.
-Draw the necessary diagrams.
Properties of video display devices- persistence, resolution, aspect ratio.

2. Explain Bresenham’s Line Drawing Algorithm with Example.
1) Input two line end points and store the left endpoint in (Xo,Yo)
2) Load (Xo,Yo) in to the frame buffer
ie) Plot in the first point
3) Calculate constants ∆x, ∆y, 2∆y, 2∆y - 2∆x and obtain the starting value
for the decision parameter as
Po = 2∆y – ∆x
4) At each X
k
along the line, starting at k=0 perform the following test
ie)

If P
K
< 0 the next point to plot is X
k
+1 , Y
k
and

P
k+1
= P
k
+2∆y
Otherwise, the next point to plot is
(X
k
+1, Y
k
+1) and P
k+1
= P
k
+ 2∆y-2∆x
5) Repeat step 4 ∆x times
Example
X1=5
Y1=10
X2=10
Y2=20
dx =5
dy=10
P = 2*dy – dx = 2*10 – 5 = 20 – 5 = 15
Increments for the successive decision parameter is
2dy=2*10=20
2dy - 2dx = 2 * 10 – 2 * 5 =20 – 10 =10
If 5 > 10 (false)
X=5
Y=10
Xend =10
Setpixel(5,10)
While 5 < 10
X=6
If (15<0) then ( false)
P + = 2dydx
Y=10+1 =11
P= 10 + 2 * (15-10) = 10+10=20
Setpixel ( 6, 11)
Etc
….
Procedure
Procedure linebres(xa , ya ,xb ,yb : integer)
Var
dx, dy, x, y, xEnd, p : integer ;
begin
dx := abs(xa – xb) ;
dy := abs(ya – yb) ;
p := 2* dy – dx ;
if xa > xb then
be gin
x := xb ;
y := yb ;
xEnd := xa;
end
else
begin
x := xa ;
y := ya ;
xEnd := xb;
end
setpixel ( x, y, 1);
While x < xEnd do
Begin
x := x + 1 ;
if p < 0 then p := p + 2 * dy;
else
Begin
y := y+1;
p := p + 2 * (dy – dx );
End
Setpixel (x, y, 1);
End
End (Line Bres)


3. Define Clipping. Write and explain Cohen – Sutherland line clipping
algorithm.
A Procedure that identifies those portions of a picture that are either inside or
outside of a specified region of space is referred to as a Clipping
In this method processing of line segments by performing initial tests that
reduce the number of intersections that must be calculated. Every line endpoint in a
picture
is assigned a four-digit binary code , called region code that identifies the location of
the point relative to the boundaries of the clipping rectangle. Regions are setup in
reference to the boundaries . Each bit position in the region code is used to indicate
one of the four relative coordinate positions of the point with respect to the clip
window: to the left ,right, top or bottom. By numbering the bit positions in the region
code as 1 through 4 from right to left, the coordinate regions can be correlated with
the bit positions are

bit 1 : left
bit 2 : right
bit 3 : below
bit 4 : above
pic
A value of 1 in any bit position indicates that the point is in relative position;
Otherwise the bit position is set to 0. If a point is within the clipping rectangle,
The region code is 0000. Apoint that is below and to the left of the rectangle has a region
code of 0101.

Bit values in the region code are determined by comparing endpoint coordinate values
(x,y) to the clip boundaries. Pic.
Bit 1 is set to 1 if x < xwmin . The other three bit values are determined using similar
comparisions.
Region code bit values can be determined with following 2 steps
1) Calculate differences between endpoint coordinates and clipping boundaries.
2) Use the resultant sign bit of each difference calculation to set the corresponding
value in the region code.

Bit 1 is the sign bit of x-xwmin
Bit 2 xwmax – x
Bit 3 y – ywmin
Bit 4 ywmax – y

Pic)
Intersection points with a clipping boundary can be calculated nusing the slope intercept
form of the line equation . for a line with endpoint coordinates (x1 , y1) and ( x2, y2)
the y coordinate of the intersection point with a vertical boundary can be obtained with
the calculation
y = y1 + m(x-x1)
where x value is set either to xwmin or to xwmax and the slope of the line is calculated as
m = (y2 – y1) / ( x2 – x1)
similarly ,the x coordinate can be calculated as
x = x1 + ( y-y1)/m
with y set either to ywmin to ywmax
Algorithm for line clipping for cohen Sutherland line clipping method.

4. Explain Reflection and shearing.

A reflection is a transformation that produces a mirror image of an object. The
mirror image for a two dimensional reflection is generated relative to an axis of reflection
by rotating the object 180
0
about the reflection axis. We can choose an axis of reflection
in the xy plane or perpendicular to xy plane. When the reflection axis is a line in the xy
plane, the rotation path about this axis is in a plane perpendicular to the xy plane, the
rotation path is in the xy plane.

Pic.

Reflection about the line y = 0 , the x axis, is accomplished with the transformation
matrix

1 0 0

0 -1 0

0 0 1
pic
A reflection about the y axis flips x coordinates while keeping y coordinates the same.
The matrix for this transformation is




-1 0 0

0 1 0

0 0 1

pic
We flip both the x and y coordinates of a point by reflecting relative to an axis that is
perpendicular to the xy plane and that passes through the coordinate origin. This
transformation has the matrix representation

-1 0 0

0 -1 0

0 0 1

pic
If we choose the reflection axis as a diagonal line y = x the reflection matrix is

0 1 0

1 0 0

0 0 1

pic
To obtain a transformation matrix for reflection about the diagonal y = -x
We could concatenate the matrices for the transformation sequence
1. Clockwise rotation by 45
0

2. reflection about y axis and
3. counter clockwise rotation by 45
0


the resulting transformation matrix is

0 -1 0

-1 0 0

0 0 1


Shearing
A transformation that distorts the shape of an object such that the transformed
Shape appears as if the object were composed of internal layers that had been caused to
slide over each other is called a shear.

pic
An x- direction shear relative to the x axis is produced with the transformation matrix

1 shx 0

0 1 0

0 0 1

which transforms coordinate positions as

x’ = x+shx
y’=y

An real number can be assigned to the shear parameter shx. A coordinate position (x,y) is
then shifted horizontally by an amount proportional to its distance ( y value) from the x
axis (y=0) Setting shx to 2 for example, changes the square into parallelogram.
Pic
Negative values for shx shift coordinate positions to the left.

We can generate x – direction shears relative to other reference lines with

1 shx -shx . yref

0 1 0

0 0 1

with coordinate positions transformed as

x’= x+shx(y-yref)
y’= y
pic
A Y direction shear relative to the line x=xref generated with the transformation matrix


1 0 0

shy 1 -shy . xref

0 0 1
pic
which generates transformed coordinate positions

x’= x
y’= shy(x-xref)+y
This transformation shifts a coordinate position vertically by an an amount proportional
to its distance from the reference line x = xref

5. Explain Basic Transformations with procedure
Transformation
Changes in orientation , size, and shape are accomplished with geometric
Transformations that alter the coordinate descriptions of the object

The basic transformations are
a) Translation
b) Rotation
c) Scaling

Translation
A translation is applied to an object by repositioning it along a straight line
path from one coordinate location to another. We translate a 2 dimensional point by
adding translation distances tx and ty , to the original coordinate position (x, y) to
move the point to a new position (x’, y’)

x’ = x + tx
y’ = y + ty

The translation distance pair (tx, ty) is called translation vector or shift vector.
We can express the translation equations as a single matrix equation by using column
vectors to represent coordinate positions and the translation vector


P = x1 P’ = x1’ T = tx

x2 x2’ ty


Therefore P’ = P + T

Fig
Rotation
A 2 dimensional rotation is applied to an object by repositioning it along a
circular path in the xy plane. To generate a rotation , we specify a rotation angle
theta and the position (xr, yr) of the rotation point about which the object is to be
rotated.

We first determine the transformation equations for rotation of a point position P
when the pivot point is at coordinate origin. Fig
Using the standard trigonometric identities , we can express the transformed
coordinates in terms of angles Θ and ф is

x’ = rcos(ф + Θ) = rcos фcos Θ – rsin ф sin Θ
y’ = rsin (ф + Θ) = rcosфsin Θ + rsinфcos Θ ---------I

The original coordinates of the point in polar coordinates are
x= rcos ф and y= rsin ф --------------------II

Substituting the values of II to I we obtain the transformation equations for rotating a
point at position (x,y) through an angle Θ about the origin

x’= xcos Θ - ysin Θ
y’=xsin Θ - ycos Θ


Therefore,
P’ = R . P

Scaling
Scaling transformation alters the size of an object. This operation can be carried out for
polygons by multiplying the coordinate values ( x, y) of each vertex by scaling factors sx
and sy to produce the transformed coordinates (x’, y’ )

x’ = x . sx
y’ = y.sy

Scaling factor sx scales objects in the x direction, which sy scales in the y direction.
The matrix form of transformation is


x’ = sx 0 x
0 sy . y
y’

P’ = S . P
When sx and sy are assigned the same value,a uniform scaling is produced that maintains
relative object proportions. Unequal values for sx and sy result in a differential scaling
hat is often used in design applications.

We can control the location of a scaled object by choosing a position , called the fixed
point that is to remain unchanged after the scaling transformation.
Pic
Coordinates for the fixed point (xf,yf) can be chosen as one of the vertices.

For a vertex with coordinates (x,y) the scaled coordinates (x’ ,y’) are calculated as
x’ = xf + ( x – xf )sx
y’= yf + (y - yf) sy

We can rewrite these scaling transformations to separate the multiplicative and additive
terms.

x’= x.sx + xf(1-sx)
y’= y.sy +yf(1-sy)

where the additive terms xf(1 – sx ) and yf( 1- sy) are constant for all points in the object.

6. Explain i) LCD
ii) LED
i) LCD (Liquid Crystal Display)
Used in TV, calculator, etc.
Produce picture by passing polarized light from the surrounding or from an internal light
source through a liquid crystal materials
Liquid crystal refers the fact that these compounds have a crystalline arrangement of
molecules . They flow like a liquid. So it called LCD.
Requires two glass plates. Each contains a light polarized at right angles to each other .
Rows of horizontal transparent conductor contains one glass plate. Columns of vertical
transparent conductor contains another glass plate.
Intersections of two defines a pixel position. Molecules are aligned on “On State”.
Polarized light passing through the material is twisted. So that it passes to the opposite
polarizer. Then light is reflected back to the view. To
Turn off the pixel apply voltage to the two intersecting conductors so that the light is not
twisted. This is referred as passive matrix.
Pixel is stored in frame buffer. Refresh at a rate of 60 frames/ sec
Another Method for constructing LCD’s
Place a transistor at each pixel position using thin film transistor. Transistors are used to
control the voltage at pixel locations to prevent charge from leaking out of the liquid
crystal.
ii)LED (Light Emitting Diodes)
A matrix of diodes are arranged to form the pixel positions to display. The pixture
definition is stored in refresh buffer Just like scan line , it need data from the refresh
buffer and convert into voltage level depends upon the intensity value that are applied to
diodes.

7. Explain projections in detail
Projection is mainly classified as
a. Parallel projection
b. Perspective projection
Parallel projection
Co-ordinate positions are transformed to the view along the parallel line.
We can specify a parallel projection with a projection vector that defines
the direction for the projection lines.

Orthographic Parallel Projection
When the projection is perpendicular to the plane it is called Orthographic Parallel
Projection
It is used to produce front , rear and top views of an object. Front and rear are called
elevations. And top view is called plane view.
We can also form orthographic projections that display more than one face of an object.
Such views are called Axonometric Projections.
Eg. Isometric Projections
Isometric Projection
Aligning the projection plane so that it intersects each coordinate axis in which the object
is defined at the same distance from the origin.
If the view plane is placed in the Zvp along Zv axis and any point (x,y,z) in viewing
coordinate is transformed to projection co ordinates as
Xp = x
Yp=y
Where Z - > depth Information
Pic
Obilique projection
View plane is not perpendicular to projected line
Oblique projection is specified with two angles α , ф
Point x,y,z is projected to (xp, yp) to the viewplane.
Orthographic projection is (x,y)
α is angle with the line on the projection plane.
L is Line length
Ф is angle of the line on the projection plane.
Projection co ordinates are
Xp = x+ Lcos ф
Yp = y+Lsin ф
The position of the point on Z axis is
Tan α =Z/L
L=z/ Tan α =ZL1

Perspective Projection
Object positions are transformed to the view plane along lines that converge to a point
called projection.
We transform points along projection lines that meet at the PRP
We set the projection reference point at position Zprp along Zv axis and the view plane at
Zvp
Let x’ , y’ , z’ be any of point on the projection line then the eqns are
X’= x-xu
Y’=y-yu
Z’= z-(z-zprp)U
U can have values from o to 1
When U = 0 , position P = (x, y, z)
When U = 1 , Position P = (0,0,Zprp)

8. Explain Bezier Curves in detail
Bezier curve uses spline approximation method and widely used in CAD. This was
developed by French Engineer Pierre Bezier
Bezier Curves
Curve section is approximated and their relative position determine the degree of
polynomial
Blending Function specification is convenient
N+1 control points , Pk = (xk, yk, zk) with K From 0 to n. They can be blended to P(U)
which describes path between P0 and Pu
P(U)= ∑
n
k=0
Pk BEZ k,n(U)
Bezier blending functions BEZ
k,n
(U) are the Bernstein Polynomials
BEZ
k,n
(U) = C(n,k) U
k
(1-U)
n-k

We can define Bezier Blending functions with recursive calculation
BEZ
k,n
(U) =(1-U) BEZ
k,n-1
+ U BEZ
k-1,n-1
(U)
With BEZ
k,k
= U
k
and BEZ
0,k
=(1-U)
k
The curve lies within the convex hull. The blending functions are all positive and their
sum is always 1
Convex Rule property ensures the polynomial smoothly follows the control point.
Cubic Bezier Curves
Many graphics packages provide only cubic spline function. They are generated with four
control points.
Four blending functions for cubic Bezier Curve is obtained by putting n=3
BEZ
0,3
(U) = (1-U)
3

BEZ
1,3
(U) = 3U(1-U)
2
BEZ
2,3
(U) = 3U
2
(1-U)
BEZ
3,3
(U) = U
3

Properties of Bezier Curves
Always passes through the first and last control point
The boundary conditions at two ends are
P(0) = Po
P(1) =Pn

9. Explain animation in detail
The term computer animation generally refers to any time sequence of visual changes in a
scene
Design of animation sequence
Steps are
1. Story board layout
2. Object definitions
3. Key frame specification
4. generation of in between frames
For frame by fame animation, each frame of the scene is separately generated and
stores. The story board is an outline of the action. It defines the motion sequence as a set
of basic events that are to take place. Depending on the type of animation to be produced.
The story board is an outline of the action.
An Object definition is given for each participant in the action. Objects can be defined in
terms of basic shapes such as polygons or splines.
A key frame is a detailed drawing of the scene at a certain time in the
Animation sequence.
There are several other tasks that may be required , depending on the application. They
include motion verification , editing and production
And synchronization of a sound track.
General computer animation Functions
Object manipulations and rendering , camera motions and the generation of in betweens
One function available in animation package is provided to store and manage the object
data base
Another typical function stimulates camera movements.
Raster Animations
A simple method for translation in the xy plane is to transfer a rectangular block of pixel
values from one location to another
To rotate a block of pixels, we need to determine the percent of area coverage for
those pixels that overlap the rotated block.


10. Explain i) Back face Detection method
ii) Depth buffer method for detection
i. Back Face Detection Method
A fast and simple object space method for identify the backface of a polyhedron is
based on the inside outside tests.
A point (x, y, z) is inside the polygon surfaces with plane parameters A,B,C, & D if
Ax + By+Cz + D<0
When an inside point is along the line of sight to the surface, the polygon must be a
backface.
If N is normal vector to the polygon surface , V is a vector viewing direction from eye
or camera then this polygon is a backface
V . N > 0
ii) Depth Buffer Method (Z – Buffer Method)

Image space approach for polygon surfaces. Each pixel position (x,y) on view plane ,
object depth can be compared by compared Z values. Z ranges from 0 to Zmax, z max
can be set to 0 or to the largest value.
Two buffers are necessary. A depth buffer is used to store depth values of each (x,y)
position and refresh buffer to store intensity for each position. Intensity buffer is set
to 0(min) and refresh buffer is initialized to background intensity.
The depth is calculated for each position . If it is greater than value stored in depth
buffer, the new value is stored.
The Algorithm is
1. Initialize the depth buffer & refresh buffer. So that depth (x,y) =0 refresh (x,y)=1
2. For each position on each polygon surface compare depth values to previously
stored values in the depth buffer to determine visibility.
Calculate the depth z for each (x, y) position on the polygon
If Z < depth (x,y) then set depth (x,y) = Z
refresh (x, y) =Isurf (x, y)
I is the value for background intensity.

11. Explain applications of Computer graphics
• Image Processing
• Computer Aided Design (CAD)
• Education
• Entertainment
• Graphical User Interface (GUI)
• Morphing
• Animation
• Visual Programming

12. Explain a. Depth Cueing b. Surface Rendering
a.Depth Cueing

A simple method for indicating depth with wire frame displays is to vary the
intensity of objects according to their distance from the viewing position
- Line closest to the viewing position are displayed with highest intensities
- Lines Farther - > Decreasing Intensities

Uses
Choosing maximum and minimum intensities
Range of distances over which the intensities are to vary
Modeling the effect of atmosphere

b. Surface Rendering

Realism is attained by setting the surface intensity of objects according to
1. Lighting conditions in the scene
- The intensity and positions of light sources
- The general background illumination required for a scene
2. Assigned surface characteristics
- Degree of transparency
- How rough or how smooth the surfaces to be.


13. Explain 3D transformations in detail
Inclusion of Z coordinates
Translation
Explanation
Matrix form
Rotation
Explanation
Matrix Form
Scaling
Explanation
Matrix Form

14. Explain the classification of Visible surface Detection methods with example.
Broadly classified in to 2 categories
i. Object space methods
Compare objects and part of objects to each other within the scene
definition to which surfaces as a whole should label as visible

Eg. Back face detection

Back Face Detection Method
A fast and simple object space method for identify the backface of a polyhedron is
based on the inside outside tests.
A point (x, y, z) is inside the polygon surfaces with plane parameters A,B,C, & D if
Ax + By+Cz + D<0
When an inside point is along the line of sight to the surface, the polygon must be a
backface.
If N is normal vector to the polygon surface , V is a vector viewing direction from eye
or camera then this polygon is a backface
V . N > 0

ii. Image space methods

Visibility is decided point by point at each pixel position on the projection plane
Eg. Depth buffer method
ii) Depth Buffer Method (Z – Buffer Method)

Image space approach for polygon surfaces. Each pixel position (x,y) on view plane ,
object depth can be compared by compared Z values. Z ranges from 0 to Zmax, z max
can be set to 0 or to the largest value.
Two buffers are necessary. A depth buffer is used to store depth values of each (x,y)
position and refresh buffer to store intensity for each position. Intensity buffer is set
to 0(min) and refresh buffer is initialized to background intensity.
The depth is calculated for each position. If it is greater than value stored in depth
buffer, the new value is stored.
The Algorithm is
3. Initialize the depth buffer & refresh buffer. So that depth (x,y) =0 refresh (x,y)=1
4. For each position on each polygon surface compare depth values to previously
stored values in the depth buffer to determine visibility.
Calculate the depth z for each (x, y) position on the polygon
If Z < depth (x,y) then set depth (x,y) = Z
refresh (x, y) =Isurf (x, y)
I is the value for background intensity.

15. Explain about the following.
(i). Flat panel displays (10)
(ii).Graphics Software (6)
(i).Explain: Flat panel display- (10)
emissive display-plasma panel, thin film electro luminescent display,
light emitting diode.
non emissive display- liquid crystal display.
(ii). Short notes on graphics software (6)

16. (i).Show how the shear transformation may be expressed in terms of rotation and
scaling.(8)
(ii). Scale the polygon with coordinates A(2,5), B(7,10) and C(10,2) by two
units in x direction and two units in y direction. (8)


17. Briefly explain about DDA line drawing algorithm .Give one example using
this algorithm.(16)
Explain about DDA line drawing algorithm. Write algorithm and give one
example using this algorithm.(16)

18. Explain about the following.
(i).Shadow mask method (8)
(ii).Liquid crystal display(8)
Explain about the following
(i).Shadow mask method (8)
(ii).Liquid crystal display(8)

19. Explain the basic Building blocks of multimedia?
Text
Image
Sound
Video
Animation

20. How will you manipulate images and graphics in multimedia? Explain in
detail.
Images
Making still images
Bitmaps
Graphics

21. What are the various aspects of video signal? Explain in detail. Give details
about computer video formats also.
Recording formats
Digital Video

22. What are the basic tools that are required for the multimedia Software?
Explain in detail.

o Text Editing & Word Processing Tools
o Painting & Drawing Tools
o Image – Editing Tools
o Sound Editing Tools
o Animation, video & Digital Movie Tools

23. What are the various input and output devices that can be used in a
Multimedia PC? Explain in detail.
Input devices

• Keyboards
• Mouse
• Trackball
• Touch screens
• Magnetic card Encoders & Readers
• Graphic tablets
• Flat – bed scanner
• Optical Character Recognition
• Infrared Remote
• Voice Recognition
• Digital Cameras

Output devices

• Audio devices
• Amplifier & Speaker
• Monitors
• Video Devices
• Projectors
• Printers

24. Explain the Multimedia communication in detail?
Collaborative Computing.
GC Architecture.
Conferencing.
Session management.
Centralized and distributed architecture
Layer’s protocols

25. Explain the presentation requirements
Lip synchronization requirements.
Pointer synchronization requirements.
Elementary media synchronization.