APJ Abdul Kalam University,India
KTU University
Course Name : Computer Graphics and Image processing
Course code : CST 304
Course year: Btech semester 6 (3rd year)
Summary notes of modules for exam preparation
Module 1: Basics of Computer Graphics and its Applications
This module introduces the foundational concepts of computer graphics, focusing on hardware (display
devices) and basic algorithms.
1. Basics of Computer Graphics and its Applications
What is Computer Graphics?
Computer graphics involves creating, manipulating, and displaying visual content using computers. It spans
2D and 3D rendering, animations, simulations, and virtual reality.
Applications:
Entertainment: Video games, movies, and animations (e.g., Pixar films).
Design: CAD (Computer-Aided Design) for architecture, engineering (e.g., AutoCAD).
Visualization: Scientific data visualization (e.g., weather maps, medical imaging).
Education: Interactive learning tools and simulations.
Virtual Reality: Immersive environments for gaming, training (e.g., flight simulators).
Key Concepts:
Graphics pipeline: The process of transforming 3D models into 2D images on a screen (modeling,
transformation, rasterization, shading).
Pixels: The smallest addressable elements on a screen.
Resolution: The number of pixels (e.g., 1920x1080).
2. Video Display Devices
Overview: These are hardware devices that display graphical output.
Types:
CRT (Cathode Ray Tube): Older technology using electron beams to excite phosphors on a screen. It supports
high refresh rates but is bulky.
LCD (Liquid Crystal Display): Uses liquid crystals to modulate light. Common in modern monitors, thinner
and more energy-efficient than CRTs.
LED Displays: Use light-emitting diodes for better color and contrast.
OLED Displays: Organic LEDs that emit light directly, offering superior contrast and flexibility.
Key Features:Refresh rate: How often the screen updates (e.g., 60 Hz).
Resolution: Determines the clarity of the display.
Color depth: Number of colors a display can show (e.g., 8-bit per channel = 16.7 million colors).
3. Refresh Cathode Ray Tubes
How CRTs Work:
An electron gun emits electrons, which are deflected by magnetic fields to hit a phosphor-coated screen.The
phosphors glow when struck, creating an image.The screen is "refreshed" by scanning the electron beam
across it repeatedly (e.g., 60 times per second).
, Refresh Mechanism:The refresh rate prevents flickering (e.g., 60 Hz means the screen redraws 60 times per
second).
Interlaced vs. Non-Interlaced: Interlaced scans alternate lines for efficiency, while non-interlaced scans all
lines sequentially for better quality.
4. Random Scan Displays and Systems
Random Scan (Vector Scan):
Unlike raster scans (which draw line by line), random scan displays draw images as a series of lines (vectors)
directly.Used in early computer graphics systems (e.g., oscilloscopes).
Mechanism:The electron beam moves directly between points to draw lines, rather than scanning the entire
screen.Suitable for line drawings (e.g., wireframe models) but not for filled shapes or complex images.
Advantages:High resolution for line drawings.No need for a full-screen refresh.
Disadvantages:Cannot display shaded or filled areas.Limited to simple graphics.
5. Raster Scan Displays and Systems
Raster Scan:
The electron beam scans the screen line by line (horizontally), from top to bottom, to create an image.Each
line is made of pixels, and the image is stored as a grid of pixels (a bitmap).
Mechanism:The frame buffer (memory) stores pixel values (color/intensity).The beam refreshes the screen at
a fixed rate (e.g., 60 Hz).
Advantages:Can display complex images, including filled shapes and textures.Standard for modern displays
(LCD, LED).
Disadvantages:Requires more memory (frame buffer).Lower resolution for fine details compared to random
scan.
6. Line Drawing Algorithms
Purpose: To draw straight lines on a raster display by determining which pixels to illuminate.
DDA (Digital Differential Analyzer) Algorithm:
Calculates intermediate points between two given points (x1, y1) and (x2, y2).
Uses the slope of the line to decide which pixels to light up.
Steps:
Compute the difference in x and y coordinates (Δx, Δy).
Determine the number of steps based on the larger difference.
Increment x and y coordinates proportionally and round to the nearest pixel.
Bresenham’s Line Drawing Algorithm:
An optimized algorithm that uses integer arithmetic to minimize calculations.
Steps:
Start at (x1, y1).
Calculate the decision parameter to decide whether to increment y or not while moving along x.
Plot pixels iteratively until reaching (x2, y2).
Advantages: Faster and more efficient than DDA, widely used in graphics hardware.
7. Circle Drawing Algorithm –
Midpoint Circle Generation Algorithm
Purpose: To draw a circle on a raster display by calculating pixel positions.
Midpoint Circle Algorithm:
Uses the circle equation \( x^2 + y^2 = r^2 \) and the midpoint method to decide which pixels to plot.
Steps:
Start with a point on the circle (e.g., (r, 0)).
Use symmetry: A circle has 8-way symmetry, so calculating one octant (0° to 45°) is enough.
For each step, calculate the midpoint between two possible pixels and choose the one closest to the circle.
Plot pixels in all 8 octants using symmetry.
KTU University
Course Name : Computer Graphics and Image processing
Course code : CST 304
Course year: Btech semester 6 (3rd year)
Summary notes of modules for exam preparation
Module 1: Basics of Computer Graphics and its Applications
This module introduces the foundational concepts of computer graphics, focusing on hardware (display
devices) and basic algorithms.
1. Basics of Computer Graphics and its Applications
What is Computer Graphics?
Computer graphics involves creating, manipulating, and displaying visual content using computers. It spans
2D and 3D rendering, animations, simulations, and virtual reality.
Applications:
Entertainment: Video games, movies, and animations (e.g., Pixar films).
Design: CAD (Computer-Aided Design) for architecture, engineering (e.g., AutoCAD).
Visualization: Scientific data visualization (e.g., weather maps, medical imaging).
Education: Interactive learning tools and simulations.
Virtual Reality: Immersive environments for gaming, training (e.g., flight simulators).
Key Concepts:
Graphics pipeline: The process of transforming 3D models into 2D images on a screen (modeling,
transformation, rasterization, shading).
Pixels: The smallest addressable elements on a screen.
Resolution: The number of pixels (e.g., 1920x1080).
2. Video Display Devices
Overview: These are hardware devices that display graphical output.
Types:
CRT (Cathode Ray Tube): Older technology using electron beams to excite phosphors on a screen. It supports
high refresh rates but is bulky.
LCD (Liquid Crystal Display): Uses liquid crystals to modulate light. Common in modern monitors, thinner
and more energy-efficient than CRTs.
LED Displays: Use light-emitting diodes for better color and contrast.
OLED Displays: Organic LEDs that emit light directly, offering superior contrast and flexibility.
Key Features:Refresh rate: How often the screen updates (e.g., 60 Hz).
Resolution: Determines the clarity of the display.
Color depth: Number of colors a display can show (e.g., 8-bit per channel = 16.7 million colors).
3. Refresh Cathode Ray Tubes
How CRTs Work:
An electron gun emits electrons, which are deflected by magnetic fields to hit a phosphor-coated screen.The
phosphors glow when struck, creating an image.The screen is "refreshed" by scanning the electron beam
across it repeatedly (e.g., 60 times per second).
, Refresh Mechanism:The refresh rate prevents flickering (e.g., 60 Hz means the screen redraws 60 times per
second).
Interlaced vs. Non-Interlaced: Interlaced scans alternate lines for efficiency, while non-interlaced scans all
lines sequentially for better quality.
4. Random Scan Displays and Systems
Random Scan (Vector Scan):
Unlike raster scans (which draw line by line), random scan displays draw images as a series of lines (vectors)
directly.Used in early computer graphics systems (e.g., oscilloscopes).
Mechanism:The electron beam moves directly between points to draw lines, rather than scanning the entire
screen.Suitable for line drawings (e.g., wireframe models) but not for filled shapes or complex images.
Advantages:High resolution for line drawings.No need for a full-screen refresh.
Disadvantages:Cannot display shaded or filled areas.Limited to simple graphics.
5. Raster Scan Displays and Systems
Raster Scan:
The electron beam scans the screen line by line (horizontally), from top to bottom, to create an image.Each
line is made of pixels, and the image is stored as a grid of pixels (a bitmap).
Mechanism:The frame buffer (memory) stores pixel values (color/intensity).The beam refreshes the screen at
a fixed rate (e.g., 60 Hz).
Advantages:Can display complex images, including filled shapes and textures.Standard for modern displays
(LCD, LED).
Disadvantages:Requires more memory (frame buffer).Lower resolution for fine details compared to random
scan.
6. Line Drawing Algorithms
Purpose: To draw straight lines on a raster display by determining which pixels to illuminate.
DDA (Digital Differential Analyzer) Algorithm:
Calculates intermediate points between two given points (x1, y1) and (x2, y2).
Uses the slope of the line to decide which pixels to light up.
Steps:
Compute the difference in x and y coordinates (Δx, Δy).
Determine the number of steps based on the larger difference.
Increment x and y coordinates proportionally and round to the nearest pixel.
Bresenham’s Line Drawing Algorithm:
An optimized algorithm that uses integer arithmetic to minimize calculations.
Steps:
Start at (x1, y1).
Calculate the decision parameter to decide whether to increment y or not while moving along x.
Plot pixels iteratively until reaching (x2, y2).
Advantages: Faster and more efficient than DDA, widely used in graphics hardware.
7. Circle Drawing Algorithm –
Midpoint Circle Generation Algorithm
Purpose: To draw a circle on a raster display by calculating pixel positions.
Midpoint Circle Algorithm:
Uses the circle equation \( x^2 + y^2 = r^2 \) and the midpoint method to decide which pixels to plot.
Steps:
Start with a point on the circle (e.g., (r, 0)).
Use symmetry: A circle has 8-way symmetry, so calculating one octant (0° to 45°) is enough.
For each step, calculate the midpoint between two possible pixels and choose the one closest to the circle.
Plot pixels in all 8 octants using symmetry.
