CGA Q-Bank SCA, KIIT [ 2 marks type] (a) Differentiate window and viewport.

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.

WINDOW

VIEWPORT

(b) What is dithering?

Dithering is the attempt by a computer program to approximate a color from a mixture of other colors when the required color is not available. (c) Comment on the raster and random display mechanisms used in graphics terminal.

In a raster scan displays the electron beam is swept across the screen, one row at a time from top to bottom. Contrasting in random scan displays the electron beam is directed to the parts of the screen where a picture is to be drawn. (d) Compare and contrast bitmap and vector images.

Bitmap (or raster) images are stored as a series of tiny dots called pixels. Each pixel is actually a very small square that is assigned a color, and then arranged in a pattern to form the image Vector images are not based on pixel patterns, but instead use mathematical formulas to draw lines and curves that can be combined to create an image from geometric objects such as circles and polygons. (e) Consider two different raster systems with resolutions of HD and Full-HD. What size is frame buffer (in bytes) for each of these systems to store an image in True-color?

True color = 24-bits = 3 Bytes For HD 720x1280x3 Bytes For Full HD 1080x1920x3 Bytes (f) Define shadow masking. The shadow mask is one of the technologies used to manufacture cathode ray tube (CRT) televisions and computer displays that produce color images. (g) Translate a triangle with vertices at original coordinates (10, 20), (10, 10), (20, 10) by tx=5, ty=10.

(h) A unit square is transformed by 2 x 2 transformation matrix. The resulting position vector are :[email protected]

What is the transformation matrix?

(i) Briefly discuss the types of seed-fill algorithms. Seed Fill Approaches: 2 algorithms: Boundary Fill and Flood Fill works at the pixel level and suitable for interactive painting applications. (j)

What are namable and unnamable curves? Give examples.

Curves are classified into two categories- namable, unnamable. Namable curves known as true-curve generation approach (planes, spheres, parabolas, circles, straight lines) Unnamable Curves are having no specific names. They can take any shape. (k) Distinguish Interactive and Non-interactive computer graphics with suitable example.

Ans: Interactive Computer Graphics: Interactive Computer Graphics involves a two way communication between computer and user. Here the observer is given some control over the image by providing him with an input device for example the video game controller of the ping pong game. This helps him to signal his request to the computer. Non Interactive Computer Graphics: In non-interactive computer graphics otherwise known as passive computer graphics. It is the computer graphics in which user does not have any kind of control over the image. Image is merely the product of static stored program and will work according to the instructions given in the program linearly. The image is totally under the control of program instructions not under the user. Example: screen savers. (l)

Define persistence in terms of CRT Phosphorous.

Ans: Persistence is the one of the major property of phosphorous used in CRT’s. It means how long they continue to emit light after the electron beam is removed. (m) What is the need of homogeneous coordinates?

Ans: 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.

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(n) Write down the equation of a standard ellipse both in Cartesian and Polar form.

Ans:

(o) What is the need of the concept of “Shading in computer Graphics”? List the merits of Phong shading.

Ans: In computer graphics, shading refers to the process of altering the color of an object/surface/polygon in the 3D scene, based on its angle to lights and its distance from lights to create a photorealistic effect. Shading is performed during the rendering process by a program called a Shader. Phong Shading overcomes some of the disadvantages of Gouraud Shading and specular reflection can be successfully incorporated in the scheme. The first stage in the process is the same as for the Gouraud Shading - for any polygon we evaluate the vertex normals. Merits: Usually very smooth-looking results High quality, narrow specularities.

(p) What do you mean by Perspective projection?

Ans: Perspective projection is one in which the lines of projection are not parallel. Instead, they all converge at a single point.

(q) Derive the Translation matrix in 3D.

Ans: Scalling about x-axis

(r)

Rotation about z-axis

Translation about y-axis

Briefly discuss the RGB and CMY color model.

Ans:

Cyan = RGB – R, Magenta = RGB – G, Yellow = GRB – B

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(s)

Define computer graphics animation?

Ans: 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. (t) Differentiate Random scan and Raster scan displays.

Ans: 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. (u) What are the different properties of phosphorus? (v) List out the merits and demerits of Penetration techniques. (w) Differentiate between ambient light and diffused light. (x) Write down the both x and y direction shear transformation matrix. (y) What do you mean by quadric surfaces? (z) Calculate the width (in cm) of an image of aspect ratio 16:9 with height 360cm. (aa) Differentiate between impact and non-impact printers. (bb) A point (4,3) is rotated counterclockwise by an angle of 45°. Find the rotation matrix and the resultant point. (cc) What do you mean by parallel projection? (dd) What are the different ways of specifying spline curve? (ee) Briefly discuss the methods for Visible surface detection. (ff) What is a sphere? Also, specify its equation in parametric form. (gg) State the relationship between RGB and HSV color models. (hh) What are the types of Orthographic projection? Give examples. (ii) Define tweening in computer animation. (jj) Consider a raster system with the resolution in 720p and the color palette calls for 65,536 colors. What is the minimum amount of video RAM that the computer must have to support the abovementioned resolution and number of colors? (kk) While drawing a circle, co-ordinates of only one eighth of the total pixels lying on circumference of a circle are computed. Why? (ll) What are the different ways of specifying spline curve? (mm) Define key-frames in animation. (nn) What is anti- aliasing? List its type. (oo) What do you mean by retracing? Define horizontal as well as vertical retracing. (pp) Compare and contrast bitmap and vector images. (qq) Consider two different raster systems with resolutions of HD and Full-HD. How much storage (in bytes) is required for each system if 16 bits per pixel are to be stored? (rr) What are the acceptance and rejection test-bit codes in Cohen-Sutherland Line clipping algorithm? (ss) Write down the equation of a standard circle both in Cartesian and Polar form. (tt) Derive the four inequalities for Liang-Barsky Line clipping algorithm. (uu) List the types of Orthographic projection. Give examples. (vv) Explain with example the need for visible surface detection. [email protected]

Long type (a) Explain with neat diagram the construction & working color CRT monitors.

CRT Diagram Components and description Image formation (b) Consider a raster system with the resolution in 720p and the color palette calls for 65,536 colors. What is the minimum amount of video RAM that the computer must have to support the above-mentioned resolution and number of colors?

720p means the pixel map is 720x1280. 65,536 means is a 16-bit color = 2 Bytes Total Video RAM = 720x1280x2 Bytes (c) What is the importance of computer graphics in present scenario? Describe four major application areas of it. (d) Digitize a line from (20, 10) to (30, 18) on a raster screen using Bresenham’s straight line algorithm.

• We plot the initial point (x0, y0) = (20, 10), and determine successive pixel positions along the line path from the

decision parameter as:

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(e) Derive the equation for two dimensional rotation by an angle theta, with a reference point (x r,yr). If a straight line connecting two points (2,3) and (6,7) is rotated by an angle of 30 degrees with (5,5) as a reference point, find the end points of the rotated line.

(f) Explain three dimensional transformation and its type. Translation / Scaling / Rotation / Sheering Representation: Matrix Form (Homogeneous) (g) Derive the three dimensional rotation matrix about Y-axis with rotation angle 90 degrees.

(h) Write down the equation of a standard ellipse both in Cartesian and Polar form. Also write the Ellipse generating Algorithm/ pseudo-code. (i) An ellipse is a two dimensional closed curve that satisfies the equation:

(ii) Mid-point Ellipse drawing Algorithm/ pseudo-code

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(i) Define Polygon. What are the types of Polygons? Give example of each.

A polygon is any 2-dimensional shape formed with straight lines. Triangles, quadrilaterals, pentagons, and hexagons are all examples of polygons. The name tells you how many sides the shape has. Types of Polygons: Convex and Concave Convex Polygons: In a convex polygon, any line segment joining any two inside points lies inside the polygon. Concave Polygons: In a concave polygon, a line segment connecting any two points may or may not lie inside the polygon. (j) Explain in detail about the DDA scan conversion algorithm. Also compute its complexity.

Scan converting lines • Input: two pixel locations (x1,y1) and (x2,y2) in device coordinates • Goal: determine the intermediate pixels to paint to connect the points Line equation: y = mx + b line_eq(x1,y1,x2,y2): m = (y2-y1) / float(x2-x1) b = y1 - m * x1 if x2 > x1: dx = 1 else: dx = -1 while x1 != x2: y = m * x1 + b paint(x1, round(y)) x1 += dx • Problem: If the slope is > 1, the line is not continuous, pixels are skipped. This method therefore requires an enormous number of floating-point multiplications, and is therefore expensive.

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(k) What makes Bresenham's algorithm more efficient than the basic DDA? Factors: Arithmetic, Operations, Speed, Drawing, Accuracy & Efficiency . (l) Write a boundary-fill procedure to fill an 8-connected region.

Algorithm with proper description. (m) Explain how an ellipse displayed with the midpoint method could be properly filled with a boundary-fill algorithm. Mid-point Ellipse drawing Algorithm Boundary-fill algorithm (n) Explain in detail the Sutherland-Hodgman polygon clipping algorithm with an example.

Details of the algorithm with proper figure for each points (L-R and T-B) (o) What is convex hull?

In mathematics, the convex hull or convex envelope of a set X of points in the Euclidean plane or Euclidean space is the smallest convex set that contains X. For instance, when X is a bounded subset of the plane, the convex hull may be visualized as the shape enclosed by a rubber band stretched around X. (p) (q) (r) (s) (t)

Describe Depth Buffer hidden surface elimination method. Explain Ellipse generating Algorithm. Explain the coding scheme of Cohen Sutherland line clipping algorithm. What is clipping? Describe Liang–Barsky Line clipping algorithm. Compare the Cohen-Sutherland and Liang-Barsky line clipping algorithms on the basis of their merits and demerits. Explain. (u) What is cubic Bezier curve? Explain in detail. (v) What is clipping? Describe Sutherland-Hodgman area clipping algorithm. (w) Explain, why there is a need for visible surface detection? (x) With suitable examples, explain all 3D transformations. (y) A square shown in (fig-a) is converted to a parallelogram shown in (fig-b) using composite transformation matrix M. Determine M.

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(z) Define the following terms:

a. b. c. d. e. f. g. h.

Radial Intensity Attenuation. Convex hull. Ambient Light. Persistence Antialiasing Path specification types in Computer Animation Gouraud Surface Rendering RGB to YIQ matrix.

2 4 2 2 2 4 2 2

(aa) Explain the types of seed-fill Algorithms. Write C-function/ pseudo-code for this with 4-connected and 8-connected regions. (bb) What do mean by the interpolation and approximation splines? Give the procedure for spline specifications? (cc) Define vanishing point. Is the location of vanishing point directly related to the giving point? Explain how? (dd) What are the three basic operations of CSG? Describe any two of them with suitable example. (ee) What is depth coherence? Explain how it is able to speed up the painting of polygons in Z-buffer rendering. (ff) Derive simple illumination model. Include the contribution of diffuse, ambient and specular reflection. (gg) What are the disadvantages of using scan-conversion procedures to fill or to display an object?

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