Computer Graphics - Two Marks Questions and Answers Unit ......Computer Graphics - Two Marks Questions and Answers Unit - I 1. What is Computer Graphics? Computer graphics is the use

B.Sc CS – Semester V (UCS15E01) Prepared by U.Udayakumar Assistant Professor

Computer Graphics - Two Marks Questions and Answers

Unit - I

1. What is Computer Graphics?

Computer graphics is the use of computers to display and manipulate information in

graphical or pictorial form, either on a virtual display unit or via a printer or plotter.

2. What is 2D Computer graphics?

A picture that has height and width but no depth is two-dimensional (2-D).

2D computer graphics are the computer-based generation of digital images mostly from

two-dimensional models, such as 2D geometric models, text and digital images.

3. What is 3D Computer graphics?

A picture that has or appears to have height, width and depth is three-dimensional (3-D)

3D computer graphics compared to 2D computer graphics that uses three dimensional

representation of geometric data.

3D graphics are essential to realistic computer games, simulators and objects.

4. What is Computer Animation?

Computer animation is the art of creating moving images via the use of computers.

It is created by means of 3D computer graphics, though 2D computer graphics are still

widely used for stylistic, bandwidth, and faster real-time rendering needs.

5. What is a pixel?

In computer graphics, pictures or graphics objects are presented as a collection of discrete

picture elements called pixels. The pixel is the smallest addressable screen element.

6. Define Scan conversion.

The process of representing continuous picture or graphics object as a collection of discrete

pixels is called scan conversion.

7. Define Rasterization.

The process of determining the appropriate pixels for representing picture or graphics object

is known as rasterization.

8. Write the application of computer graphics

User interfaces

Plotting of graphics and chart

Office automation and Desktop publishing.

Computer aided drafting and design

Simulation and animation

Education and training


Image processing

Development of computer games

Entertainment

9. Define raster scan system.

In a raster scan system, in addition to the Central Processing Unit, CPU, a special purpose

processor, called the video controller or display controller is used to control the operation of

the display device.

10. Define random scan system

In random scan system no local memory is provided for scan conversion algorithms, since

the functionality is typically implemented using PLAs (Programmable Login Arrays) or

microcode.

11. What are the features of graphics workstation.

They can be configured from 8 to 24 bits per pixel with higher screen resolutions, faster

processor and other option available in high-end systems.

They may have multiscreen system called the Media Wall, which provides a large wall-

size display area.

They have multiple input and output devices.

12. What is meant by frame buffers?

The CPU and system memory work exactly in similar manner as in non-graphics computer

system. However, in raster scan displays a special area of memory is dedicated to graphics

only. This memory area is called Frame buffer.

13. What is the function of control grid and focusing system in CRT?

The Control grid voltage determines the velocity achieved by the electrons before hit

the phosphor. The control grid voltage determines how many electrons are actually in

the electron beam.

The focusing system concentrates the electron beam so that the beam converges to a

small point when it hits the phosphor coating.

14. Define persistence.

Persistence is defined as the time it takes the emitted light from the screen to decay to one-

tenth of its original intensity.

15. Define resolution.

Resolution indicates the maximum number of points that can be displayed without overlap

on the CRT. It is defined as the number of points per centimeter that can be plotted

horizontally and vertically.


16. What are the elements of graphics workstations?

Graphics workstation is the graphics kernel system’s (GKS) term for a graphical device

that can display graphical output or accept graphical input or both.

It consists of Central Processing Unit(CPU), display processor, memory, display devices,

recorder, plotter, joy stick, keyboard, mouse, light pen, scanner etc.

The main hardware components of a graphics workstation are CPU and display

processor. The display processor is also called a graphics controller.

It makes CPU free form the graphics chores. In addition to the system memory, a separate

display processor memory area is provided in graphics workstation.

17. Define CRT

A CRT is an evacuated glass tube. An electron gun at the rear of the tube produces a beam

of electrons which is directed towards the front of the tube by a high voltage typically 15000

to 20000 volts.

18. List out the input devices in computer graphics

Keyboard

Mouse

Trackball

Trackpads

Touch Screens

Joystick

Light pen

Data Glove

Scanners

19. Define DDA.

The vector generation algorithms which step along the line to determine the pixel which

should be turned on are sometimes called Digital Differential Analyzer(DDA).

It is used to find intermediate points in between the starting point and ending point.

20. Define Bresenham’s line algorithm.

The basic principle of bresenham’s line algorithm is to select the optimum raster locations to

represent a straight line. To accomplish the algorithm always increments either x or y by one

unit depending on the slope of line.

21. What are the advantages of DDA?

It is the simplest algorithm and it does not require special skills for implementation

It is a faster method for calculating pixel positions than the direct use of equation y=mx+b.


Unit - II

1. Define midpoint circle algorithm.

The midpoint circle drawing algorithm also uses the eight-way symmetry of the circle to

generate it. It is used to determine the points needed for rasterizing a circle.

2. Define midpoint ellipse algorithm.

It is very similar to midpoint circle algorithm. However the four way symmetry property we

need to consider the entire elliptical curve in the first quadrant.

3. Define scan line polygon filling algorithm and its steps.

Scan line polygon filling algorithm is used for solid color filling in polygons.

Steps

1. Find the intersection of the of the scan line with all edges of the polygon.

2. Sort the intersections by increasing x-coordinate i.e. from left to right.

3. Make the pairs of the intersections and fill in color with in all the pixels inside the pair.

4. Define odd-even rule.

In odd-even rule we draw a line from any position p to a distant point outside the coordinate

extents of the object and count the number of edges crossing along the line.

If the number of edges crossed by the line is ODD then the point p is in the interior.

If the number of edges crossed by the line is EVEN then the point p is in the exterior.

5. Define non-zero winding rule.

In non-zero winding number method we need to know the direction of each edges in the

polygon, i.e. whether the edge is clockwise or counter-clockwise.

The winding number is number if times the polygon edges wind around a particular point in

the counterclockwise direction.

6. Define boundary fill algorithm.

In boundary fill algorithm starts at a pixel inside the polygon to be filled and paints the

interior proceeding outwards towards the boundary. This algorithm works only if the color

with which region has to be filled and the color of the boundary of the region are different.

7. Define flood fill algorithm.

Flood fill colors an entire area in an enclosed figure through interconnected pixels using a

single color. It connected pixels of a selected color get replaced by a fill color.

8. Define inside and outside test.

This method is also known as counting number method. While filling an object, we often

need to identify whether particular point is inside the object or outside it.


There are two methods by which we can identify whether particular point is inside an object

or outside.

Odd-even rule

Non zero winding number rule

Odd-even rule:

In odd-even rule we draw a line from any position p to a distant point outside the coordinate

extents of the object and count the number of edges crossing along the line.

If the number of edges crossed by the line is ODD then the point p is in the interior.

If the number of edges crossed by the line is EVEN then the point p is in the exterior.

Non zero winding rule:

In non-zero winding number method we need to know the direction of each edges in the

polygon, i.e. whether the edge is clockwise or counter-clockwise.

The winding number is number if times the polygon edges wind around a particular point in

the counterclockwise direction.

9. Write about spline curves.

A spline curve is a mathematical representation for which it is easy to build an interface that

will allow a user to design and control the shape of complex curves and surfaces. A curve

that actually passes through each control point is called an interpolating curve; a curve that

passes near to the control points but not necessarily through them is called an approximating

curve.

10. Write the syntax of fill area function

Void floodfill(int x,int y, int border).

Flood fill function is used to fill an enclosed area. Current fill pattern and fill color is used to

fill the area (x,y) is any point on the screen.


Unit – 3

1. What do you mean by “ATTRIBUTES”?

Attributes are properties or characteristics assigned to a primitive which decide how the

entity will look like.

For example you specify width of the line to be drawn. So “width” is the attribute of the

primitive “line” which decides how thick or thin the line will appear.

2. What is Line Attributes? Give example.

Line contain 3 attributes

Line width

Line color

Line type

Line width

The line width depends on capability of the device to display it. In raster scan display the

standard width line (or default line) is drawn with one pixel at each sample position.

The command to set line width is:

SetLineWidthScaleFactor(lw)

Line color

When we draw a line the default color of the line is displayed like for example the color of

the line drawn in Microsoft paint is black.

The command to set line color is:

SetPolyLineColorIndex(lc).

Line Type

There are 3 types of lines:

Solid Line

Dashed Line

Dotted Line

Solid line is the default line which is drawn with complete solid section for the length

specified.

The command to set line type is:

SetLinetype(lt).


3. Define Line cap and its types.

We can adjust the shape of the line ends to give them a better appearance by adding line

caps.

Types

Butt cap

Round cap

Projected Square cap

4. Define buttcap.

Buttcap is obtained by adjusting the end of positions of the component parallel lines so that

the thick line is displayed with square ends that are perpendicular to the line path.

5. Define Round cap

Round cap obtained by adding a filled semicircle to each butt cap. The circular arcs are

centered on the line endpoints and have a diameter equal to the line thickness.

6. Define Projected square cap.

Projected square cap extend the line and add butt caps that are positioned one-half of the line

width beyond the specified endpoints.

7. Define milter join.

A milter join accomplished by extending the outer boundaries of each of the two lines until

they meet.

8. Define round join

A round join is produced by capping the connection between the two segments with a

circular boundary whose diameter is equal to the width.

9. Define bevel join

A bevel join is generated by displaying the line segment with but caps and filling in

triangular cap where the segments meet.

10. Define area fill attributes

Area fill attributes for filling a defined region include a choice between a solid color or a

pattern fill and choices for particular colors and patterns.

Fill styles

Hollow

Solid

Patterned

Diagonal Hatch fill

Diagonal cross hatch fill


11. Define character attributes.

The appearance of displayed character is controlled by attributes such as font, size, color and

orientation. Attributes can be set both for entire character strings (text) and for individual

characters defined as marker symbols.

12. Define Text attributes

The choice of font or type face is set of characters with a particular design style as courier,

Helevetica, times new roman and various symbols. The characters in a selected font also be

displayed with styles bold, italics and underline or shadow styles.

setTextFont(tf)

13. Define translation

Translation is a process of changing the position of an object in a straight line path from one

coordinate location to another.

14. Define rotation

A two 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 and the position of the

rotation point about which the object is to be rotated.

15. Define scaling.

A scaling transformation changes the size of the 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’).

16. What is meant by window to viewport transformation?

The window coordinates are transferred to viewing coordinates we choose the window extent

in viewing coordinates and select the viewport limits in normalized coordinates.

17. Define clipping

The procedure that identifies the portions of a picture that are either inside or outside of a

specified region of space is referred to as clipping. The region against which an object is to

be clipped is called a clip window or clipping window.

18. Define line clipping.

The line are said to be interior to the clipping window and hence visible if both end points

are interior to the window. If both end points of a line are exterior to the window, the line is

not necessarily completely exterior to the window.


19. What are the types of clipping?

1. Point clipping

2. Line clipping

3. Area clipping

4. Curve clipping

5. Text clipping

20. Define viewing

The process of displaying an image of a picture involves mapping the coordinates of the

points and lines that form the picture into the appropriate physical devices coordinate where

the image is to be displayed.

Unit – IV

1. Define parallel projection

In parallel projection, z coordinate is discarded and parallel lines from each vertex on the

object are extended until they intersect the view plane. The point of intersection is the

projection of the vertex.

2. Define perspective projection

The perspective projection, on the other hand, produces realistic views but does not preserve

relative proportions. In perspective projection, the lines of projection are not parallel.

Instead they all coverage at a single point called the center of projection or projection

reference point.

3. Define surface rendering.

Surface rendering involves setting the surface intensity of objects according to the lighting

conditions in the scene and according to assigned surface characteristics. The lighting

conditions specify the intensity and positions of light sources and the general background

illumination required for a scene.

4. Define spline curves.

Spline curves are the curves defined by the piece-wise smooth polynomial function and

possesses a high degree of smoothness at the places where the polynomial piece connect.

5. Define 2D transformation

Transformation are a fundamental part of the computer graphics. Transformation are the

movement of the object in Cartesian plane. When the transformation takes place on a 3D

plane. It is called 3D transformation.

Translation

Scaling

Rotation


6. Write down uses of surface rendering?

Surface rendering is used in a number of industries such as in health care. There parts of the

body are rendered so doctors can closely examine specific areas of a patient or wounds they

may have incurred. Archaelogists also use rendering to make an image of very fragile

objects in order to examine them without harming them.

7. What the purpose using exploded & cutaway in 3D.

Cutaway: It is a 3D graphics, drawing, diagram and or illustration, in which surface

elements of a three-dimensional model are selectively removed, to make internal features

visible, but without sacrificing the outer context entirely.

Exploded: An exploded view is a diagram, picture, schematic or technical drawing of an

object, that shows the relationship or order of assembly of various parts.

8. Define Bezier curves.

Bezier curve is an approach for the construction of the curve. A Bezier curve is determined

by a defining polygon. Bezier curves have a number of properties that make them highly

useful and convenient for curve and surface design.

9. State any two properties of Bezier curve.

The basis functions are real.

Bezier curve always passes through the first and last control points i.e. curve has same end

points as the guiding polygon.

The curve generally follows the shape of the defining polygon.

10. Write about 3D transformations.

3D Translation

o Translation is a process of changing the position of an object in a straight line

path from one coordinate location to another.

3D Scaling

o A two 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 and the position of the rotation point about which the object is to be

rotated.

3D Rotation

o A two dimensional rotation is applied to an object by repositioning it along a

circular path in the xy plane.

3D Reflection

o It can be performed relative to a selected reflection axis or with respect to a

selected reflection plane.


3D Shears

o It is used to modify the shape of the object and they are useful in three-

dimensional viewing for obtaining general projection transformation.

Unit – 5

1. What do you mean by visible surface determination or hidden line elimination?

A set of 3D objects and viewing specification to determine lines or surfaces of the objects

are visible, so that we can display only the visible lines or surfaces. This process is

known as hidden surfaces or hidden line elimination or visible surface determination.

2. Define object-space method.

Object-space method is implemented in the physical co-ordinate in which objects are

described.

It compares objects and parts of the objects to each other within the scene definition to

determine which surfaces as a whole label are visible. Object-space method used in line-

display algorithms.

3. Define Image-space method.

Image-space method is implemented in the screen co-ordinate system in which the

objects are viewed.

In an image-space algorithm, visibility is decided point by point at each pixel position on

the view plane.

4. Define z-buffer algorithm.

The simplest and commonly used image space approach to eliminate hidden surfaces is

the z-buffer or depth buffer algorithm. It is developed by catmull.

This algorithm compares surface depths at each pixel position on the projection plane.

5. Write down the advantages of z-buffer algorithm.

It is easy to implement.

It can be implemented in hardware to overcome the speed problem.

The algorithm processes objects one at a time, the total number of polygons in a

picture can be arbitrarily large.

6. Define Computer Animation.

The term computer animation refers to anytime sequence of visual changes in a

scene.

In computer generated animation, various transformations, along with variations

in object color, transparency or surface texture are displayed with time variation.

We can also produce computer animations by changing lighting effects or other

parameters and procedures associated with illumination and rendering.


7. Define key frame systems.

In key frame systems, We can separate the frames into individual components or objects

called cells. Given the animation paths, we can interpolate the positions of individual

objects.

8. Define morphing.

Transformation of object shapes from one form to another is called as morphing. key

frames for an object transformation, we first adjust the object specification in one of the

frames so that the number of polygon edges or vertices is the same for the two frames.

9. Define motion specifications.

A technique for motion specification in computer animation for the interactive

specification and real-time evaluation of the movements of geometrical objects with

several degrees.

Direct Motion Specification

The rotation angles and translation vectors. The geometric transformations are

applied to transform coordinate positions.

Goal directed systems

It can specify the motions that are to take place in general terms that abstractly

describe the actions.

Kinematics and Dynamics

We can construct animation sequences using kinematic or dynamic descriptions.

We specify animation by giving motion parameters like position, velocity and

acceleration parameters.

Inverse Kinematics and dynamics

It can specify the initial and final positions of the object and calculations are done

by the computer

10. List out any four computer animation software.

Autodesk Maya

Blender

Autodesk 3ds max

Adobe flash

Cinema 4D

Adobe After Effects

11. Define Raster Animations

In raster systems, we generate real – time animation in limited application using raster

operation. Such as 2D or 3D transformations on objects. It can also animate objects along

2D motion paths using the color – table transformation.


12. List out computer animation functions.

Animation packages, such as wave front, provide special functions for designing the

animation and processing individual objects.

Some steps included in the development of animation sequence are

Object manipulation and rendering

Camera motions

Object motion generation (2D or 3D transformations)

Object rendering

13. Write down the design of animation sequences.

Storyboard layout

Object definitions

Key frame specifications

Generation of in - between frames

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Computer Graphics - Two Marks Questions and Answers Unit ......Computer Graphics - Two Marks Questions and Answers Unit - I 1. What is Computer Graphics? Computer graphics is the use