CG Short notes

Module 1: Introduction to Computer Graphics

Definition

• Computer Graphics (CG): The pictorial representation and manipulation of data by a computer, which refers to visual images created with the help of computers.

Major Applications

1. Computer-Aided Design (CAD)

   • Utilizes computer technology for designing real or virtual objects.

   • Typically displays objects in wireframe outline form to show shape and internal features.

2. Presentation Graphics

   • Produces illustrations for reports and is commonly used to summarize data.

   • Examples include bar charts, line graphs, surface graphs, and pie charts.

3. Flight Simulators

   • Provides training for pilots, where much of their training occurs on a simulator instead of a real aircraft.

4. Entertainment

   • Extensively used in film, music videos, and television shows.

5. Education

   • Facilitates the teaching of numerous concepts and fundamentals through computer-generated models.

6. Digital Art

   • Refers to art created digitally, transforming traditional activities like painting and sculpture, alongside new forms such as net art and virtual reality.

Key Concepts

Pixel

• Definition: The smallest element of an image on a computer display, represented as a dot or square.

• Properties: Every pixel has a unique logical address and can display only one color at a time.

Frame Buffer

• Definition: Memory area that holds the frame data being sent to the screen.

• Size: The size corresponds to the maximum image displayable and can be part of the graphics card or regular memory.

Raster Scan Display

• Functioning: An electron beam sweeps across the screen row by row, creating illuminated spots by toggling beam intensity.

• Characteristics: Refresh rates range from 60 to 80 frames per second; stores intensity values for screen points (pixels).

Random Scan Display

• Working: The electron beam operates like a pencil, directed to the specific part of the screen where an image needs to be drawn.

• Refresh Display File: Stores line-drawing commands to define the picture, refreshing 30 to 60 times a second.

Display Devices

1. Cathode Ray Tubes (CRT)

   • Specialized vacuum tubes producing images when an electron beam strikes a phosphorescent surface.

   • Main Parts: Includes the electron gun, deflection system, fluorescent screen, glass tube, and base.

2. Color CRT Monitors

   • Use phosphors emitting various colored light; techniques include:

     • Beam Penetration Method: Two phosphor layers, with colors based on electron penetration.

     • Shadow Penetration Method: Produces a wider color range using RGB dot arrangements per pixel.

3. Flat-Panel Displays

   • Thinner and lighter compared to CRTs, with higher resolution and lower power requirements.

   • Types:

     • Emissive Displays: Convert electrical energy to light.

     • Non-Emissive Displays: Utilize optical effects to create images.

Plasma Panels Displays

• Comprised of small fluorescent lights influenced by a voltage to emit color.

• Essential components include cathodes, anodes, and fluorescent cells.

• Advantages: High resolution and large sizes; Disadvantages: Complexity in wiring and potentially lower resolution.

LED - Light Emitting Diode

• Uses a matrix of diodes for pixel formation with definitions stored in a refresh buffer.

LCD - Liquid Crystal Display

• Picture is produced by passing polarized light through a liquid-crystal material.

• Advantages: Low power, small size, and cost-effective.

• Disadvantages: Temperature-dependent and limited contrast.

Persistence

• Refers to the state of an object or process that remains even after cessation or power-off.

Resolution

• Indicates the clarity of an image, particularly in monitors and printers, referring to the number of dots per inch (dpi).

Module 2: Scan Conversion

Overview

• Process of representing graphics objects as discrete pixels, converting continuous graphics into quantifiable data.

Scan Conversion of Lines

• Defined using endpoints and an equation, where (x1, y1) and (x2, y2) describe endpoints.

• Calculated using the equation of a line: y = mx + b to determine coordinates between endpoints.

Properties of Good Line Drawing Algorithm

1. Straight appearance of lines.

2. Accurate plotting of lines.

3. Consistent dot density and spacing irrespective of length or angle.

4. Rapid rendering capability.

DDA Algorithm (Digital Differential Analyzer)

• Incremental method calculating pixel positions using previous results.

• Advantages: Fast calculations, simple additions.

• Disadvantages: Round-off errors and time-consuming rounding.

Scan Conversion of Circles

• Circles are symmetric in eight ways; calculating points in one octant can derive the remaining seven using symmetry.

Bresenham's Circle Algorithm

• Utilizes efficient integer arithmetic for rendering circles without floating-point operations.

Scan Line Polygon Filling Algorithm

• A method intersecting scanlines with polygon edges to fill between intersections with specific ordered steps.

Module 3: Two-Dimensional Transformation

Definition

• Transformation on a 2D plane involves repositioning or altering graphics.

Types of Basic Transformations

1. Translation

   • Repositions graphics along a straight path using translation distances tx and ty for points (x, y) to new positions (x', y').

2. Rotation

   • Alters angle of an object using a specified angle θ and pivot point (xr, yr).

3. Scaling

   • Changes size via scaling factors Sx and Sy affecting coordinates of vertices.

Composite Transformations

• Involve multiple transformations applied to an object (preimage) to produce a new figure (image).

• Could combine translation, rotation, and scaling.

Other Transformations

Reflection

• Produces a mirror image of an object, which can be across either the x-axis or y-axis, or perpendicular to the xy-plane.