COMPUTER GRAPHICS QUESTION BANK

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.
35    What is the purpose of presentation graphics?
    Presentation graphics is used to produce illustrations for reports or to generate 35- mm slides or transparencies for use with projectors.Presentation graphics is commonly used to summarize financial, statical,mathematical, scientific, and economic data for research reports ,managerial reports, consumer information bulletins, and other types of reports.
36    Define refresh buffer/frame buffer.
    The memory area where in picture definition is stored is called Refresh buffer. This memory area holds the set of intensity values for all the screen points. On a black and white system with one bit per pixel, the frame buffer is called a bitmap.
37    What is DDA?
    The Digital Differential Analyzer is a scan-conversion line algorithm based on calculating either difference in y-coordinate (dy) or difference in x-coordinate. We sample the line at unit intervals in one coordinate and determine corresponding integer values nearest the line path for the other coordinate.
38     What are the disadvantages of DDA algorithm?
• Round-off error in successive additions of the floating-point increment can cause the calculated pixel positions to drift away from the true line path for long line segments. • Rounding operations and floating-point arithmetic in procedure are still timeconsuming.
39     What is attribute parameter?
Any parameter that affects the way a primitive is to be displayed is referred to as an attribute parameter.
40    What are the basic line attributes?
Basic attributes of a straight line segment are its type, its width, and its color

PART – B

1     Explain Cathode Ray tube
2    Explain color CRT monitors
3    Explain direct view storage tubes
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 Bresenham Ellipse generating Algorithm
10    Explain Boundary fill Algorithm
11    Explain Cohen Sutherland line clipping algorithm.
12    Explain Cyrus Beck line clipping algorithm.
13    Explain bout video controller
14    Explain about liquid crystal displays
15    What is seedfill algothm? Explain
16    Explain about scanline 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.
14    Define Clipping.
Any 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 algorithm or simply clipping. The region against which an object is clipped is called a clip window.
15    Define Window.
 A world-coordinate area selected for display is called a window.
16    Define view port.
An area on a display device to which a window is mapped is called a view port.
17    What is viewing transformation?
The mapping of a part of a world-coordinate scene to device coordinates is referred to as viewing transformation.
18    What are the types of Clipping?
• Point clipping
• Line clipping
• Area clipping
• Curve clipping
• Text clipping
19    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.
20    Define coherence properties?
A coherence property of a scene is apart of a scene by which relate one part of the scene with the other parts of the scene.

PART – B

1    Explain reflection and shear in 2D transformation?
2    Explain translation, Rotation and Scaling in 2D transformation?
3    Prove that successive 2D Scaling are Commutative.
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?
8    Prove that Successive 2D Translations are additive
9    Prove that Successive 2D Rotations are multiplicative
10    Prove that Successive 2D Scaling are multiplicative


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.
22    List out the 3D Issues?
More Complicated Objects than 2D
More involved geometric transformations
Viewing transformations much more complicated
Projection onto a two dimensional output display (usually)
Identification of Visible Surfaces

PART – B

1    Give the 3-D transformation matrix for
    Translation
    Scaling
    Rotation
    Reflection
    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
9    Explain Oblique projection
10    Prove that Successive 3D Translations are additive
11    Prove that Successive 3D Rotations are multiplicative
12    Prove that Successive 3D Scaling are multiplicative
13    Prove that successive 3D Scaling are Commutative.


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
    Domain
    Unambiguity
    Uniqueness
    Accuracy
    Validness
    Closure
    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.
    The solid representation methods are
    Wireframe model
    Sweep representations
    Spatial Partitioning representations
    Octree representation
    Boundary Representation (B-rep)
    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?
    Surface are stored in order of decreasing depth
    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?
    Surface identifier
    Depth
    RGB intensity
    Opacity parameter
    Percentage of area coverage
    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
    Device Independent
    Platform Independent; SGI Irix,Linux,Windows
    Abstractions(GL,GLU,GLUT)
    Open surface
    Hardware-independent software interface
    Support of client-server protocol
13    List some features of OpenGL
    Performance
    Lighting
    Transparency and Alpha blending
    Rendering in 3D
    Abstract co-ordinate system
    Color specification
    Drawing primitives
    Textures
Use of Hardware
14    List the libraries used in the OpenGL
     The libraries used in OpenGL are
    GL
    GLU
    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
    It displays more realistic highlights on a surface
    It greatly reduces the Mach-band effect
    It gives more accurate results
21   
What is meant by Rendering?
In 3D graphics rendering means the calculation of the final image from the scene that includes models, textures, lights, special effects and cameras. The final image will be 2D image made of pixels. Utilizing materials, lighting techniques, and renderer’s settings one can render multitude of different images from a single 3D scene.
22    Types of Rendering?
    Realistic rendering
    Clay Rendering
    Wire Rendering
23    List the advantages of flat shading?
    inexpensive to compute
    Appropriate for objects with flat surface
    Less pleasant for smooth surfaces


PART – B

1    Explain the following models
    Ambient Light
    Diffuse Illumination
    Pont-source Illumination
2    Explain the following models
    Specular Reflection
    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