080230030 Computer Graphics 2 MARKS QUESTIONS AND ANSWERS
UNIT – I
PART – A
1
|
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
|
2
|
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.
|
3
|
What is meant by refreshing of the screen?
Some method is needed for
maintaining the picture on the screen. Refreshing of screen is done by
keeping the phosphorus glowing to redraw the picture repeatedly. (i.e.)By
quickly directing the electronic beam back to the same points.
|
4
|
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.
|
5
|
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.
|
6
|
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
|
7
|
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.
|
8
|
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.
|
9
|
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.
|
10
|
What is resolution?
The maximum number of points that can be
displayed without an overlap on a CRT is called as resolution.
|
11
|
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.
|
12
|
What is meant by Addressability?
The Addressability is the
number of individual dots per inch (d.p.i) that can be\ created. If the
address of the current dot is (x, y) then the next dot will be (x+y), (x+y+1)
etc.
|
13
|
What is a dot size?
Dot size may be defined as the
diameter of a single dot on the devices output. Dot size is also called as
the Spot size.
|
14
|
What is interdot distance?
Interdot distance is the
reciprocal of addressability. If the addressability is large, the interdot
distance will be less. The interdot distance should be less to get smooth
shapes
|
15
|
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.
|
16
|
What are the features of Inkjet printers?
• They can print 2 to 4
pages/minutes.
• Resolution is about
360d.p.i. Therefore better print quality is achieved.
• The operating cost is very
low. The only part that requires replacement
is ink cartridge.
• 4 colors cyane, yellow,
majenta, black are available.
|
18
|
What are the advantages of electrostatic plotters?
• They are faster than pen
plotters and very high quality printers.
• Recent electrostatic plotters
include a scan-conversion capability.
• Color electrostatic plotters
are available. They make multiple passes
over the paper to plot color
pictures.
|
19
|
Define pixel?
Pixel is shortened forms of
picture element. Each screen point is referred to as pixel or pel.
|
20
|
What is frame buffer?
Picture definition is stored in
a memory area called frame buffer or refresh
buffer.
|
21
|
What is bitmap and what is pixmap?
The frame buffer used in the
black and white system is known as bitmap which take one bit per pixel. For
systems with multiple bits per pixel, the frame buffer is often referred to
as a pixmap.
|
22
|
What is a Vector display or stroke writing or
calligraphic display?
Random scan monitors draw a
picture one line at a time and for this reason are also referred as vector
displays.
|
23
|
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.
|
24
|
What do you mean by 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.
|
25
|
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.
|
26
|
What is an output primitive?
Graphics programming packages
provide function to describe a scene in terms of these basic geometric
structures, referred to as output primitives.
|
27
|
What do you mean by ‘jaggies’?
Line with stair step appearance is
known as jaggies.
|
28
|
Distinguish between convex and concave polygons?
If the line joining any two points in
the polygon lies completely inside the polygon then, they are known as convex
polygons. If the line joining any two points in the polygon lies outside the
polygon then, they are known as concave polygons.
|
29
|
What is seed fill?
One way to fill a polygon is to start
from a given point (seed) known to be inside the polygon and highlight
outward from this point i.e neighboring pixels until encounter the boundary
pixels, this approach is called seed fill.
|
30
|
What is scan line algorithm?
One way to fill the polygon is to
apply the inside test. i.e to check whether the pixel is inside the polygon
or outside the polygon and then highlight the pixel which lie inside the
polygon. This approach is known as scan-line algorithm.
|
31
|
What is a winding number?
Winding number method is used to check
whether a given point is inside or outside the polygon. In this method give a
direction number to all the edges which cross thescan line. If the edge
starts below the line and ends above scan line give direction as -1
.otherwise1. Fr polygons or two dimensional objects, the point is said to be
inside when the value of winding number is nonzero.
|
32
|
What is tiling patterns?
The
process of filling an area with rectangular pattern is called tiling and
rectangular
fill patterns are sometimes referred to as tiling patterns.
|
33
|
What is aliasing?
In
the line drawing algorithms, all rasterzed locations do not match with the
true
line
and have to represent a straight line. This problem is severe in low
resolution
screens.
In such screens line appears like a stair-step. This effect is known as
aliasing.
|
34
|
What is anti aliasing?
The
process of adjusting intensities of the pixels along the line to minimize the
effect
of aliasing is called ant aliasing.
|
PART
– B
1
|
Explain Cathode
Ray tube?
|
2
|
Explain color CRT monitors?
|
3
|
Explain direct view storage tubes and liquid crystal
displays?
|
4
|
Explain Raster scan systems?
|
5
|
Explain Random Scan
System?
|
6
|
Explain in detail about the DDA scan conversion
algorithm?
|
7
|
Explain Bresenhams line drawing
algorithm?
|
8
|
Explain Midpoint Circle
algorithm?
|
9
|
Explain Ellipse generating
Algorithm?
|
10
|
Explain Boundary fill Algorithm?
|
UNIT – II
PART – A
1
|
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.
|
2
|
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
|
3
|
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’ =
rcos (q + f) and Y|’= r sin (q +
f).
|
4
|
What is scaling?
The
scaling transformations changes the shape of an object and can be carried out
by multiplying each vertex (x,y) by scaling factor Sx,Sy where Sx is the
scaling factor of x and Sy is the scaling factor of y.
|
5
|
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.
|
6
|
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.
|
7
|
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.
|
8
|
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.
|
9
|
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.
|
10
|
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
|
11
|
Define Affine transformation?
A
coordinate transformation of the form
X=
axxx + axyy
+ bx , y
’ ayxx + ayy
y +by
is
called a two-dimensional affine transformation. Each of the transformed
coordinates
x ‘ and y ‘ is a linear function of the original coordinates x and y , and
parameters aij and bk are constants
determined by the transformation type.
|
12
|
Distinguish between bitBlt and pixBlt?
Raster functions that manipulate
rectangular pixel arrays are generally referred to as raster ops. Moving a
block of pixels from one location to another is also called a block transfer
of pixel values. On a bilevel system, this operation is called a bitBlt
(bit-block transfer), on multilevel system t is called pixBlt.
|
13
|
List out the various Text clipping?
All or none string clipping if all
of the string is inside a clip window, keep it
otherwise
discards. All or none character clipping discard only those characters that
are not completely inside the window. Any character that either overlaps or
is outside a window boundary is clipped. Individual characters if an
individual character overlaps a clip window boundary, clip off the parts of
the character that are outside the window.
|
PART
– B
1
|
Explain reflection and shear in 2D transformation?
|
2
|
Explain translation, Rotation and
Scaling in 2D transformation?
|
3
|
Prove
that successive 2D rotations are additive.
|
4
|
Explain window to
viewport transformation?
|
5
|
Give the 3x3
homogeneous transformation matrix for each of the following transformation
sequence
i)
Rotate counter
clockwise about the origin by 450 and then scale the x-direction
by one half as large
ii)
Scale the
y-direction by twice as tall ,shift down by 1 unit and then rotate clockwise
by 300
|
6
|
Prove that 2D rotation and scaling commute if Sx=Sy or ө=nπ for integral
n and that otherwise they do not.
|
7
|
Explain about Homogeneous co-ordinate
transformation?
|
UNIT – III
PART – A
1
|
What are the
various representation schemes used in three dimensional objects?
Boundary
representation (B-res) describe the 3 dimensional object as a set of
surfaces that
separate the object interior from the environment.
Space
portioning representation – describe interior properties, by partitioning the
spatial region
containing an object into a set of small, no overlapping, contiguous
solids.
|
2
|
What Boundary
representation?
It describes a 3D
object as a set of surfaces that separate the object interior from the
environment. e.g. polygon facets and spline patches.
|
3
|
What
space-partitioning representation?
This is used to
describe interior properties, by partitioning the spatial region containing
an object in to a set of small, non-overlapping, contiguous solids.
e.g.octree.
|
4
|
What is projection?
The process of
displaying 3D objects on a 2D display is called as Projection
|
5
|
What are the types of projection?
• Perspective projection
• Parallel projection
|
6
|
What is parallel
projection?
In a parallel projection, coordinate
positions are transformed to the view plane along parallel lines
|
7
|
What is Perspective
projection?
For a perspective projection object
positions are transformed to the view plane along lines that converge to a
point called the projection reference point.
|
8
|
What
are the steps involved in 3D transformation?
• Modeling Transformation
• Viewing Transformation
• Projection Transformation
Workstation
Transformation
|
9
|
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.
|
10
|
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.
|
11
|
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.
|
12
|
What
are the different types of parallel projections?
The parallel
projections are basically categorized into two types,
depending on the
relation between the direction of projection and the normal to the
view plane. They
are orthographic parallel projection and oblique projection.
|
13
|
What
is orthographic parallel projection?
When the direction
of the projection is normal (perpendicular) to the view
plane then the
projection is known as orthographic parallel projection
|
14
|
What
is orthographic oblique projection?
When the direction
of the projection is not normal (not perpendicular) to
the view plane then
the projection is known as oblique projection.
|
15
|
What
is an axonometric orthographic projection?
The orthographic
projection can display more than one face of an object.
Such an
orthographic projection is called axonometric orthographic projection.
|
16
|
What
is cavalier projection?
The cavalier
projection is one type of oblique projection, in which the
direction of projection
makes a 45-degree angle with the view plane.
|
18
|
What
is cabinet projection?
The cabinet
projection is one type of oblique projection, in which the
direction of
projection makes a n angle of arctan (2)=63.4- with the view plane.
|
19
|
What
is vanishing point?
The perspective
projections of any set of parallel lines that are not parallel
to the projection
plane converge to appoint known as vanishing point.
|
20
|
What
do you mean by principle vanishing point?
The vanishing point
of any set of lines that are parallel to one of the three
principle axes of
an object is referred to as a principle vanishing point or axis
vanishing point.
|
21
|
What
is view reference point?
The view reference
point is the center of the viewing coordinate system. It
is often chosen to
be close to or on the surface of the some object in the scene.
|
PART
– B
1
|
Give
the 3-D transformation matrix for
Ø
Translation
Ø
Scaling
Ø
Rotation
Ø
Reflection
Ø
Shearing
|
2
|
Drive the transformation matrix for
rotation about an arbitrary axis
|
3
|
Drive
the transformation matrix for rotation about an arbitrary Plane
|
4
|
Drive the
transformation matrix for reflection about an given plane
|
5
|
Explain 3-D Viewing
transformation
|
6
|
Explain Orthographic projection
|
7
|
Explain the types of Perspective
Projection
|
8
|
Explain 3-D clipping
|
UNIT – IV
PART – A
1
|
What is solid
modeling?
The construction of
3-dimentional objects for graphics display is often referred to as solid
modeling.
|
2
|
List the properties
of good modeling or representation
Ø Domain
Ø Unambiguity
Ø Uniqueness
Ø Accuracy
Ø Validness
Ø Closure
Ø Compactness and
Efficiency
|
3
|
What do you mean by boundary points?
The points whose distance from
the object and the object’s complement is zero are called boundary points.
They need not be a part of the object.
|
4
|
What is close set and open
set?
A closed set contains all its
boundary points, whereas an open set contains none.
|
5
|
List some solid
representation methods.
Ø
The solid representation
methods are
Ø
Wireframe model
Ø
Sweep representations
Ø
Spatial Partitioning
representations
Ø
Octree representation
Ø
Boundary Representation
(B-rep)
Ø
Constructive solid
geometry(CSG)
|
6
|
What is wireframe
model?
A wireframe model consists of two
tables, the vertex table and the edge table.Each entry of the vertex table
records a vertex and its co-ordinate values, while each entry of the edge has
two components giving the two incident vertices of the edge.
|
7
|
What are Blobby
objects?
Some objects do not contain the fixed
shape but change their surface characteristics in certain motions or when
proximity to other objects.These object can be described as exhibiting
“blobbiness” and are often simply referred to as blobby objects,since their
shapes show a certain degree of fluidity
|
8
|
What is translational sweep
and rotational sweep?
The sweep in which the 2D shape is
swept along a linear path normal to the plane of the area to construct the 3D
object is translational sweep.The sweep in which the 2D shape is rotated
about an axis of rotation specified in the plane of 2
D shape to produce the 3D object is rotational sweep |
9
|
What is voxels?
Spatial-occupancy enumeration is a
special case of cell decomposition in which the object is decomposed into
identical cells arranged in a fixed, regular grid . These cells are often
called voxels(volume elements)
|
10
|
What is cuberille?
The most common common cell type is
the cube and the representation of space as a regular array of cubes is
called a cuberille.
|
11
|
What is constructive solid geometry(CSG)?
The technique for solid modeling used
to combine the volumes occupied by overlapping 3-D objects using Boolean set
operations is called constructive solid germetry(CSG)
|
12
|
What is use of hidden line
elimination removing algorithm?
The hidden line removal algorithm
determines the lines, edges, surfaces or volume that are visible or invisible
to an observer located at a specific point in space.
|
13
|
What are the four
possibilities of the surface can have with a specified area boundary?
1.surrounding
surface
2.Overlapping
surface
3.Inside
surface
4.Outside
surface
|
14
|
What are the basic
functions of depth soring method?
Ø
Surface are stored in order
of decreasing depth
Ø
Surface are scan converted
in order, starting with the surface of greatest depth
|
15
|
What is a BSP tree?
A binary space-partitioning (BSP)
tree is an efficient method for determining object visibility by painting
surfaces onto the screen from back to front, as in the painter’s algorithm.
The BSP tree is particularly useful when the view reference point changes,
but the objects in a scene are at fixed positions.
|
16
|
What do you mean by back
face removal?
The back face removal is an
algorithm by which we can identity all the back surfaces of an object and
display only the boundaries for visible surfaces.
|
17
|
List the methods used for
hidden surface elimination based on area subdivision algorithm.
1.Warnock’s
Algorithm
2.A-buffer
Algorithm
3.Weiler-Atherton
Algorithm
|
18
|
What is stored in the
surface field of A-buffer algorithm?
Ø
Surface identifier
Ø
Depth
Ø
RGB intensity
Ø
Opacity parameter
Ø
Percentage of area coverage
Ø
Other surface rendering
parameters
|
19
|
Define Octrees?
Hierarchical tree structures
called octrees, are used to represent solid objects in some graphics systems.
Medical imaging and other applications that require displays of object cross
sections commonly use octree representation
|
20
|
Name any two 3D graphics
package procedures related with visible surface detection
1.BackFace
2.DepthBuffer
|
PART
– B
1
|
Explain
Octree Representation
|
2
|
Explain Boundary Representation
(B-reps)
|
3
|
Explain
Solid Geometry (CSG)
|
4
|
Explain Wireframe
models
|
5
|
Explain Back-Face
Detection
|
6
|
Explain Z-Buffer (Depth Buffer) algorithm
|
7
|
Explain scan line algorithm
|
8.
|
Explain Depth Sort (Painter’s) Algorithm
|
9.
|
Explain BSP-Tree Method
|
10.
|
Explain Area-Subdivision Methods
|
UNIT – V
PART – A
1
|
What is the use of
shading model?
It is used to calculate the
intensity of light that we should see at a given point on the surface of the
object
|
2
|
What is diffuse
illumination?
The object may be illuminated by
light which does not come from any particular source but which comes from all
directions. When such illumination is uniform from all directions, the
illumination is called diffuse illumination
|
3
|
What is diffuse reflection?
When the reflection are constant
over each surface of the object and they are independent of the viewing
direction , the reflection is called diffuse reflection.
|
4
|
What is meant by Gouraud
shading?
The shading technique which
renders the polygon surface by linearly interpolating vertex intensity across
the surface is called Gouraud shading.
|
5
|
What is meant by Phong
shading?
The shading technique which uses
the bilinear interpolation of vertex normal instead of using vertex
intensities is called Phong shading
|
6
|
What is specular
reflection?
When we illuminate a shiny surface
such as polished metal or an apple with a bright light, we observe highlight
or bright spot on the shiny surface. This phenomenon of reflection of
incident light in a concentrated region around the specular reflection angle
is called specular reflection.
|
7
|
What
is faceted shading or flat shading?
The fast and simple method for shading polygon is constant shading
also known as faceted shading or flat shading
|
8
|
What is half toning?
The phenomenon of apparent increase
in the number of available intensities by considering combine intensity of
multiple pixels is known as halftoning
|
9
|
What is refraction?
Refraction is the bending of wave
when it enters a medium where it’s speed is different. The refraction of
light when it passes from a fast medium to a slow medium bends the light ray
toward the normal to the boundary between the two media.
|
10
|
What is coefficient
of reflection or the reflectivity?
The ratio of the light reflected
from the surface to the total incoming light to the surface is called
coefficient of reflection or the reflectivity.
|
11
|
What is OpenGL?
OpenGL is defined as a software
interface to graphics hardware. It is a 3D graphics and modeling library that
is extremely portable and very fast. OpenGL is a cross-platform standard for
3D rendering and D hardware acceleration. It is the premier environment for
developing portable, interactive 2D and 3D graphics applications
|
12
|
Why OpenGL?
It provides
Ø
Device Independent
Ø
Platform Independent; SGI
Irix,Linux,Windows
Ø
Abstractions(GL,GLU,GLUT)
Ø
Open surface
Ø
Hardware-independent
software interface
Ø
Support of client-server
protocol
|
13
|
List some features of
OpenGL
Ø
Performance
Ø
Lighting
Ø
Transparency and Alpha
blending
Ø
Rendering in 3D
Ø
Abstract co-ordinate system
Ø
Color specification
Ø
Drawing primitives
Ø
Textures
Use of Hardware |
14
|
List the libraries used in
the OpenGL
The libraries used in OpenGL are
Ø
GL
Ø
GLU
Ø
GLUT
|
15
|
What is GL?
The Gl is fundamental OpenGL
library. It provides functions that are a permanent part of OpenGL
|
16
|
What is GLU?
GLU is GL utility which helps in
the decomposition of non convex and simple polygons into simple shapes such
as triangles, and other utilities to simplify the job of the application
programmer.
|
17
|
What is GLUT?
The GL Utility Toolkit (GLUT) is
an additional library that provides a generic interface to the window system
and is available on most platform. An event driven model is used for handling
input. Callback functions that respond to input events are registered with
GLUT event loop.
|
18
|
What is Mach band?
The linear intensity
interpolation can result bright or dark intensity streaks to appear on the
surface. These bright or dark intensity streaks, are called Mach bands.
|
19
|
What is ambient light?
A simple way to model the
combination of light reflection from the various suface to produce a uniform
illumination called ambient light or background light
|
20
|
Advantages of Phong shading
Ø
It displays more realistic
highlights on a surface
Ø
It greatly reduces the
Mach-band effect
Ø
It gives more accurate
results
|
PART
– B
1
|
Explain
the following models
Ø
Ambient Light
Ø
Diffuse
Illumination
Ø
Pont-source
Illumination
|
2
|
Explain
the following models
Ø Specular Reflection
Ø Phong Illumination Model
|
3
|
Explain
Gouraud Shading?
|
4
|
Explain Phong
Shading?
|
5
|
Explain Halftone
Shading
|
6
|
Explain Transparency
|
7
|
Explain Basic functions of OpenGL
|
8.
|
Explain features in OpenGL
|
9.
|
Explain how OpenGL works
|
10.
|
Explain OpenGL drawing primitives
|
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