(SEM VI) THEORY EXAMINATION 2018-19 COMPUTER GRAPHICS

SECTION A – Short Answer Notes (2 Marks Each)

1. Applications of Computer Graphics

Computer graphics is widely used in engineering design (CAD/CAM), medical imaging (CT, MRI scans), entertainment (movies, games), education (simulations), scientific visualization, virtual reality, and user interface design. It helps represent complex data visually for better understanding.

2. Sutherland–Hodgman Polygon Clipping

The Sutherland–Hodgman algorithm uses four clippers, one for each boundary of the clipping window (left, right, top, bottom). The polygon is clipped successively against each boundary.

3. Aspect Ratio and Retracing

Aspect ratio is the ratio of width to height of a pixel or display screen. Retracing refers to the return of the electron beam after completing one scan line (horizontal retracing) or one frame (vertical retracing).

4. Tilting Transformation

Tilting transformation rotates an object about an arbitrary axis. Yes, the order of rotation matters because matrix multiplication is not commutative, and changing order changes the final orientation.

5. Mach Band Effect and Transparency

Mach band effect is an optical illusion where contrast between shades appears exaggerated at edges. Transparency allows objects to be partially visible through others, enhancing realism.

6. Other 2D Transformations

Apart from translation, scaling, and rotation, 2D objects can undergo reflection, shearing, and composite transformations to change orientation and shape.

7. Blobby Objects and Coherence

Blobby objects are smooth shapes formed by combining implicit surfaces. Coherence refers to spatial or temporal similarity in objects that helps optimize rendering.

SECTION B – Descriptive Answers (7 Marks Each)

1. Raster Scan System and Video Controller

A raster scan system displays images by sweeping an electron beam line by line from top to bottom. The video controller fetches pixel data from frame buffer and converts it into video signals for display.

2. Translation and Scaling of a Square

Given square ABCD, translation moves all points equally, while scaling enlarges or shrinks the object relative to origin or fixed point. Transformation matrices are used for accurate computation.

3. Rotation Matrices

Rotation matrices about X, Y, and Z axes define object orientation in 3D space. The inverse of a rotation matrix equals its transpose, proving orthogonality.

4. RGB and CMY Color Models

RGB is an additive model used in monitors, while CMY is subtractive and used in printing. RGB combines red, green, and blue light, whereas CMY absorbs light.

5. True Curve Generation Algorithm

This algorithm generates smooth curves using mathematical equations. However, it is computationally expensive and difficult to implement for real-time graphics.

SECTION C – Long Answer Questions (7 Marks Each)

1. DDA vs Bresenham Algorithm

DDA uses floating-point calculations and is slower, while Bresenham uses integer arithmetic making it faster and more efficient. Bresenham handles negative slopes effectively.

2. Mid-Point Circle Algorithm

This algorithm determines pixel positions using a decision parameter and symmetry of a circle. It avoids floating-point operations and efficiently plots circles.

3. Liang–Barsky Line Clipping Algorithm

This algorithm uses parametric equations and is faster than Cohen–Sutherland. It directly computes entering and leaving points of a line segment.

4. Window to Viewport Transformation

It maps objects from world coordinates to screen coordinates using linear scaling and translation, ensuring correct display proportions.

ADVANCED TOPICS (UNIT-WISE IMPORTANT QUESTIONS)

Projection

Projection converts 3D objects to 2D view. Parallel projection maintains shape, while perspective projection gives realistic depth.

Bezier and B-Spline Curves

Bezier curves are controlled by control points but lack local control. B-Spline curves offer better flexibility and smoothness.

Hidden Surface Removal

Depth buffer method stores depth of pixels to remove hidden surfaces, while A-buffer handles transparency and anti-aliasing.

Gouraud Shading

It interpolates vertex intensities across polygons, producing smooth shading but may miss specular highlights.