(SEM V) THEORY EXAMINATION 2021-22 COMPUTER GRAPHICS

B.Tech (Sem V) – Theory Notes & Exam Answers

SECTION A – Short Answers

a. Raster Scan vs Random Scan
Raster scan displays images by refreshing pixels line by line from top to bottom, while random scan draws lines directly using vector commands. Raster is used in TVs/monitors; random scan is used in vector displays.

b. Frame Buffer (Raster Method)
A frame buffer stores intensity/color values for each pixel on the screen and supplies them to the display controller during refresh.

c. Computer Graphics vs Image Processing
Computer graphics creates images from models; image processing modifies or analyzes existing images.

d. Pixel Ratio vs Aspect Ratio
Pixel ratio is width-to-height of a pixel; aspect ratio is width-to-height of the display image.

e. Stroke vs Bitmap Character Generation
Stroke method draws characters using line segments (scalable); bitmap uses pixel patterns (fixed resolution).

f. 3-D Geometry
Represents objects using x, y, z coordinates, including surfaces, volumes, and transformations in 3D space.

g. Composite Transformation
Combination of two or more transformations (translation, rotation, scaling) into a single matrix.

h. 2-D Translation
Moves an object by adding translation distances (tx, ty) to each point: (x’, y’) = (x+tx, y+ty).

i. Properties of Bezier Curves
Pass through first and last control points, lie within convex hull, smooth and continuous, control points influence shape.

j. Specular Reflection
Mirror-like reflection producing highlights; depends on viewer position and surface shininess.

SECTION B – Descriptive Answers

Shadow Mask CRT

A shadow mask CRT uses a metal mask to align electron beams with colored phosphors.
Advantages: good color accuracy, simple design
Disadvantages: low brightness, mask heating

3-D Clipping & Perspective Problems

3-D clipping removes invisible portions of objects outside view volume. Perspective projection faces issues like depth distortion and clipping complexity.

Clipping & Liang–Barsky Algorithm

Clipping removes parts outside a window. Liang–Barsky uses parametric line equations and is faster than Cohen–Sutherland.

Reflection & Reflection About Arbitrary Line

Reflection flips objects across an axis or line. Reflection about an arbitrary line involves translating, rotating, reflecting, and reversing transforms.

Illumination Model

Total intensity = Ambient + Diffuse + Specular components, modeling realistic lighting effects.

SECTION C – Numerical & Long Answers

Pixels per Second (Refresh Rate)

Pixels/sec = Resolution × Frames/sec                     640×480 @ 60 Hz = 18,432,000 pixels/sec

1280×1024 @ 60 Hz = 78,643,200 pixels/sec

Bresenham Line Algorithm

An efficient integer-based algorithm to draw straight lines by deciding pixel positions incrementally.

Cohen–Sutherland Line Clipping

Uses region codes to quickly accept, reject, or clip a line against a rectangular window.

Mirror Reflection of Triangle

Achieved using composite transformations relative to the given mirror line.

Window-to-Viewport Transformation

Maps world window coordinates to device viewport coordinates; issues include overlap and scaling in multiple windows.

Projection: Parallel vs Perspective

Parallel keeps object size constant; perspective gives depth realism with vanishing points.

Back-Face Removal

Removes surfaces facing away from the viewer using surface normal and view vector (dot-product test).

Z-Buffer Algorithm

Stores depth (z) for each pixel; visible surface has smallest z-value. Simple and widely used.

Quadratic Surfaces

Surfaces defined by second-degree equations (sphere, cylinder, cone).

Bezier vs B-Spline & Hermite

Bezier: simple, global control                               B-Spline: local control, smoother
Hermite: defined by endpoints and tangents