UG S3 Computer Graphics, First Internal Examination, August 2024
Answer key
1. Computer Graphics
is a field of computer science that focuses on the creation, manipulation, and
representation of visual images and animations using computers. It involves the
use of hardware and software to generate and manipulate images, simulations,
and graphics that can be displayed on screens or projected in physical spaces.
2. Electron Gun,
Accelerating and Focusing Systems, Phosphor Screen, Deflection System
3. Bresenham's Line
Drawing Algorithm, DDA (Digital Differential Analyzer) Line Drawing Algorithm
4. Bitmap (Raster) Method,
Vector (Outline) Method, Stroke Method, Stroke-Based
5. Video Games
Movies and Animation
Virtual Reality (VR) and Augmented Reality (AR)
Computer-Aided Design (CAD)
3D Modeling and Rendering
Product Prototyping
Simulations and Virtual Training
6.
High-Resolution
Display: DVST could display high-resolution graphics compared
to earlier CRT systems, providing more detailed and clearer images.
Fast Refresh Rate:
The direct-write nature of DVST allowed for fast updating of images, which was
particularly useful in applications requiring real-time data visualization
(e.g., radar displays).
Persistence of
Image: The DVST had the ability to store images directly on the
screen, providing persistence without needing continuous refreshing, which
helped reduce the computational load for generating images.
7.
+------------------+
| Shadow Mask |
<--- Perforated metal sheet with holes
| (with holes) |
+------------------+
| | |
(electron beams)
v v v
+------------------+
| Phosphor |
<--- Color phosphors (Red, Green, Blue)
| Coating |
| (RGB dots or |
| stripes pattern) |
+------------------+
/ |
\
+-----------------+ / |
\ +----------------+
| Red
Electron | /
| \ | Green Electron |
|
Gun | / |
\ | Gun |
+----------------+<
| >+----------------+
| |
| |
v v
v v
+------------------------+-------------+
| CRT
Screen (Glass Tube) | |
| | Image on
| <--- Light emission from
phosphors
+------------------------+
Screen |
+-------------+
Shadow Mask Method (for Color CRT Displays)
The Shadow
Mask Method is a technique used in color CRT (Cathode Ray Tube) displays
to produce color images. It involves a metal mask or grille placed in front of
the phosphor-coated screen to ensure that the electron beams (from the electron
gun) hit only specific phosphor regions (red, green, or blue). The method
relies on the precise alignment of the electron guns, the shadow mask, and the
phosphor pattern on the screen.
Here’s a
detailed explanation of how the Shadow Mask Method works:
Components Involved in the Shadow Mask Method
- Electron Gun: The
electron gun generates three separate electron beams, one for each primary
color—Red, Green, and Blue. These beams are directed
at the screen, where each color is emitted by the phosphor coating.
- Shadow Mask: This
is a perforated metal sheet (or sometimes a mesh) placed between the
electron gun and the screen. It contains small holes or slots that
correspond to the arrangement of colored phosphor dots or stripes on the
screen.
- Phosphor Coating: The inside of the CRT screen is coated with a layer of
phosphorescent material that emits light when struck by the electron
beams. The phosphor is usually arranged in groups of three dots
(RGB) or stripes (RGB), with each group representing one pixel.
- Deflection Coils: These electromagnetic coils control the direction of the electron
beams, causing them to scan across the screen in a raster pattern.
- Screen: The
display surface where the electron beams hit the phosphor coating to
generate visible light.
Working of the Shadow Mask Method
The basic
idea behind the shadow mask method is that it controls which electron beam
strikes which color phosphor on the screen. Here’s how it works step by step:
- Phosphor Pattern: The screen is coated with a fine grid of red, green, and blue
phosphor dots or stripes. These phosphors are arranged in a specific
pattern so that each pixel on the screen is represented by three colored
phosphor spots (or stripes).
- In the dot pattern, each pixel
consists of a tiny triangle of three dots: red, green, and blue.
- In the stripe pattern, the phosphor is
arranged in parallel vertical or horizontal stripes for each color.
- Electron Guns: The electron gun assembly consists of three electron guns: one
for red, one for green, and one for blue. These guns fire streams of
electrons toward the screen. The intensity of the electron beams
determines the brightness of the color.
- Shadow Mask: The
shadow mask is a thin metal sheet with a precise pattern of holes aligned
with the phosphor dots on the screen. Each hole in the shadow mask
corresponds to one phosphor dot (red, green, or blue).
- Function of the Mask: The shadow mask ensures that each electron beam can only hit the
appropriate color phosphor dot. For example, the red electron gun only
hits the red phosphor, the green electron gun only hits the green
phosphor, and the blue electron gun only hits the blue phosphor.
- This is achieved because the holes in the
mask only allow each beam to pass through to a specific region of the
screen.
- Deflection of Electron Beams: The deflection coils direct the electron beams to scan across the
screen in a raster pattern (left to right, top to bottom). As the beams
move across the screen, they pass through the holes in the shadow mask,
and each electron beam hits its corresponding colored phosphor dot.
- Color Mixing: Each
electron beam excites the phosphor dots, causing them to emit light in the
corresponding color. By varying the intensity of the red, green, and blue
beams, a full range of colors can be generated on the screen using additive
color mixing. The color perceived by the viewer is a combination of
the intensities of the three primary colors.
8. DVST (Direct View Storage Tube)
Direct View
Storage Tube (DVST) is a type of CRT (Cathode Ray Tube) used
for graphical display purposes, especially in early computer graphics, radar,
and military applications. The key feature of the DVST is that it can store the
image directly on the screen, unlike conventional CRTs, which require
continuous refreshing of the image.
Key Characteristics of DVST:
- Image Storage: The DVST could store images directly on the phosphor-coated
screen without the need for constant refreshing, which made it suitable
for displaying static images or maps. The image was retained on the screen
even after the electron beam was turned off.
- Electron Gun:
Similar to other CRTs, a DVST uses an electron gun to shoot beams of
electrons toward the screen. The phosphor coating on the screen emits
light when hit by these electrons.
- Persistence of Image: DVST was capable of holding an image (for a certain period) even
after the electron beam stopped writing, offering a "storage"
feature that allowed it to retain images without a refresh.
- Raster Scanning: The system still used a raster scanning technique for writing and
clearing pixels, but instead of constantly refreshing the image, the DVST
could hold it until manually erased or changed.
- Specialized Usage: DVST was widely used in applications where the image needed to be
stable for extended periods, such as radar displays, scientific
applications, and military uses.
- Phosphor Material: The phosphors used in DVST were specially selected for their
ability to retain the image for an extended time.
Advantages of DVST:
- High Resolution: DVST was able to produce high-resolution images, particularly for
applications like scientific imaging and radar systems.
- No Refresh Required: Unlike traditional CRTs, which required constant refreshing, DVST
could store static images directly on the screen.
- Suitable for Static or Semi-Static Displays: It was ideal for applications such as data visualization and
maps, where the image didn't change rapidly.
Disadvantages of DVST:
- Limited Use Cases: DVST was not suitable for fast-moving or high-refresh
applications, such as modern video displays or interactive systems.
- Cost and Complexity: DVST displays were expensive and technologically complex to
manufacture.
- Persistence Issues: The stored image could begin to degrade over time, leading to
"burn-in" or fading.
Flat-Panel Displays
Flat-panel
displays refer to modern display technologies that are thinner, lighter,
and more energy-efficient than traditional CRTs. These displays are widely used
in televisions, computer monitors, smartphones, and other electronic devices.
Unlike CRTs, which use a bulky tube to display images, flat-panel displays use
a variety of technologies to display images on a flat surface.
Types of Flat-Panel Displays:
- LCD (Liquid Crystal Display):
- Working Principle: LCDs use liquid crystals that align differently when an electric
current is applied. These crystals modulate light passing through them
from a backlight, creating the image on the screen.
- Backlighting: The backlight is typically provided by CCFL (Cold Cathode
Fluorescent Lamps) or LEDs (Light Emitting Diodes).
- Advantages:
- Thin and lightweight.
- Energy-efficient.
- Widely used in TVs, monitors, and mobile
devices.
- Disadvantages:
- Limited viewing angles.
- Lower contrast compared to OLED displays.
- Requires backlighting, which can reduce
color accuracy and black levels.
- LED (Light Emitting Diode) Display:
- Working Principle: Similar to LCDs, but the backlight is provided by LEDs.
In some cases, OLED (Organic LED) displays are considered a type
of LED display, where each pixel emits its own light, eliminating the
need for a backlight.
- Advantages:
- Better contrast, brighter images, and
thinner screens.
- More energy-efficient compared to
traditional LCDs.
- Disadvantages:
- Can be expensive.
- The image quality can vary based on the type
of LED (e.g., edge-lit vs. full-array).
- OLED (Organic Light Emitting Diode):
- Working Principle: OLEDs use organic compounds that emit light when an electric
current is applied. Each pixel generates its own light, eliminating the
need for a backlight.
- Advantages:
- True
Black Levels: OLEDs can turn off individual pixels,
creating perfect black levels and better contrast ratios.
- Better
Color Accuracy: Excellent color reproduction.
- Thin
and Flexible: OLED displays are extremely thin and
flexible, allowing for curved or even foldable screens.
- Disadvantages:
- Expensive to produce.
- Potential for "burn-in" if static
images are displayed for long periods.
- Plasma Display:
- Working Principle: Plasma displays use electrically charged gas cells to produce
light. Each cell emits light when electrically excited, and the
combination of these lights creates the image.
- Advantages:
- Excellent color accuracy and contrast
ratios.
- Wide viewing angles.
- Disadvantages:
- Heavy and bulky.
- Not as energy-efficient as LCD or LED
displays.
- Risk of burn-in with static images.
- Quantum Dot Display (QLED):
- Working Principle: QLED displays use quantum dots (tiny semiconductor particles)
that emit light when exposed to a backlight. These dots help to produce
more accurate colors and higher brightness levels than standard LCDs.
- Advantages:
- Bright, vivid colors.
- High contrast ratios and good energy
efficiency.
- Disadvantages:
- Still relies on backlighting, so can't
achieve true blacks like OLED.
Advantages of Flat-Panel Displays:
- Thin and Lightweight: Flat-panel displays are much thinner and lighter than traditional
CRTs, making them easier to transport and mount on walls.
- Energy Efficiency: Modern flat-panel displays, especially LCD and LED types, consume
much less power than CRTs.
- High Resolution: Many flat-panel displays offer high-definition resolutions
(1080p, 4K, 8K), delivering sharp and clear images.
- Wide Viewing Angles: Displays like OLED and QLED provide wider viewing angles with
less color degradation from different perspectives.
- Slim Design: They
occupy much less space, allowing for more compact and aesthetically
pleasing designs.
Disadvantages of Flat-Panel Displays:
- Limited Lifespan: Some technologies, especially OLED, may suffer from image burn-in
or degradation over time.
- Cost:
Advanced flat-panel displays, particularly OLED and QLED, can be expensive
to manufacture.
- Viewing Conditions: LCDs and LEDs can sometimes suffer from issues like glare or
limited contrast in bright lighting environments.
9. 1. Keyboard
- The keyboard is one of the primary input
devices for a computer, allowing users to input text, numbers, and
commands. It consists of an arrangement of keys that are typically divided
into groups, such as alphabetic characters, numeric keys, function keys,
and special command keys (like Control, Shift, and Alt). Each keypress
sends a signal to the computer, which interprets it as a specific
character or command.
2. Mouse
- The mouse is a pointing device that helps
users interact with graphical elements on a computer screen. It translates
the movement of the mouse across a flat surface into movements of a
pointer or cursor on the screen. Common actions performed with a mouse
include pointing, clicking, dragging, and scrolling. Many mice have
additional buttons or a scroll wheel to provide further control or shortcuts.
3. Scanner
- A scanner is an input device that digitizes
physical documents or images, converting them into digital formats that
can be stored and manipulated on a computer. It uses light sensors to
capture the details of an image or text on paper, creating an electronic
version. Scanners are commonly used for tasks such as digitizing
photographs, scanning printed documents, or converting drawings into
digital images.
10. Points
- Definition: A
point is a fundamental element in geometry that represents a precise
location in space. It has no dimensions—no length, width, or
height—meaning it does not take up any physical space.
- Representation: Points are usually represented by a dot and labeled with a
capital letter, like AAA, BBB, or PPP.
- Properties: A
point simply indicates a position or location. Multiple points can be used
to define more complex geometric shapes or lines.
Lines
- Definition: A
line is a one-dimensional figure that extends infinitely in both
directions. Unlike a point, a line has length but no thickness or width.
- Representation: Lines are often represented by two points on the line, such as AB↔\overleftrightarrow{AB}AB,
where AAA and BBB are points on the line. Alternatively, a lowercase
letter can sometimes be used to name a line.
- Types of Lines:
- Straight Line: The shortest distance between any two points.
- Curved Line: A line that bends continuously without forming sharp angles.
- Parallel Lines: Lines that never intersect and remain the same distance apart.
- Perpendicular Lines: Lines that intersect at a right (90-degree) angle.
11. CRT (Cathode Ray Tube) Monitors
A
CRT (Cathode Ray
Tube) monitor is a type of display device that was widely used
before the advent of flat-panel technologies like LCD and LED. CRT monitors use
electron beams to create images on a phosphorescent screen. Here’s a detailed
explanation of how CRT monitors work, along with a description of their
components.
Components and Working of a CRT Monitor
1. Electron Guns:
- Inside
a CRT monitor, there are three electron guns (one for each primary color:
red, green, and blue).
- Each
gun emits a stream of electrons that are directed towards the screen.
2. Focusing and Deflection System:
- The
electron beams pass through a focusing system to make them sharp and
precise, and a deflection system to guide them to specific points on the
screen.
- The
deflection system, which consists of electromagnetic coils, controls the
direction of the beams, allowing them to scan across the screen in a
horizontal pattern.
3. Phosphorescent Screen:
- The
inner surface of the CRT screen is coated with phosphor dots or stripes
that glow when struck by the electron beams.
- Each
pixel on the screen is made up of three phosphor dots—red, green, and
blue. By varying the intensity of each electron beam, different colors
are produced.
4. Image Creation:
- The
electron beams scan across the screen line by line, in a process called
raster scanning.
- As
the beams hit the phosphor coating, the dots emit light, forming an
image.
- The
image is refreshed several times per second (refresh rate), giving the
appearance of a continuous, stable picture.
Diagram
of a CRT Monitor
A
basic diagram of a CRT monitor would include:
- Electron Guns: Located
at the back of the tube, one for each color (red, green, and blue).
- Focusing
Coils:
Situated after the electron guns to focus the beams.
- Deflection
Coils:
Positioned around the tube to direct the beams to specific areas of the
screen.
Advantages
and Disadvantages
Advantages:
- Better Color
Representation: CRTs offer rich and accurate colors, making
them ideal for graphic-intensive applications.
- High Refresh
Rates:
They can support higher refresh rates, reducing motion blur in fast-moving
images.
Disadvantages:
- Bulk and
Weight:
CRT monitors are heavy and take up significant space.
- Power
Consumption:
They consume more power than modern flat-panel displays.
- Eye Strain: Lower
refresh rates can cause flicker, leading to eye strain.
12. Character Generation refers to the techniques used to
display text characters on a screen. There are various methods of character
generation, especially in computer graphics and digital displays, where
characters need to be displayed quickly and clearly. Here are the main methods
of character generation:
1. Bitmap or Dot Matrix Method
- Description: In
this method, each character is represented as a pattern of dots (pixels)
in a grid. This grid, called a matrix (e.g., 5x7 or 8x8), stores the
position of each dot that makes up the character.
- Process: When
a character is displayed, the pattern from the matrix is mapped to the
screen by turning on specific pixels to match the grid.
- Advantages:
- Simple and fast since characters are
predefined.
- Can be used to generate any character set by
loading different bitmap patterns.
- Disadvantages:
- Limited flexibility in scaling or resizing,
as larger characters become pixelated or blocky.
- Application:
Commonly used in low-resolution displays, dot matrix printers, and early
computer monitors.
2. Stroke or Vector Method
- Description:
Instead of using a grid of dots, each character is created using a set of
lines or strokes. This method involves plotting points and connecting them
to create the outline or skeleton of the character.
- Process: Each
character’s shape is defined by mathematical coordinates and line
segments, making it easy to scale without losing quality.
- Advantages:
- Scalable without distortion, so characters
can be displayed in any size.
- Sharp edges and smooth curves, even at large
sizes.
- Disadvantages:
- Requires more processing to draw each line
segment, which can be slower than the bitmap method.
- Application:
Widely used in vector graphics, CAD applications, and scalable fonts like
TrueType and PostScript.
3. Outline Method
- Description: This
method represents characters by outlining their shapes. The outline of
each character is stored as a series of mathematical curves (e.g., Bezier
curves) and lines.
- Process: When
a character is displayed, the outline is filled in to create the final
character shape. Since the outline is based on curves, it can be scaled
easily.
- Advantages:
- High-quality characters that can be scaled
without loss of resolution.
- Ideal for creating smooth and complex fonts.
- Disadvantages:
- More complex processing than bitmaps,
requiring more computational power.
- Application: Used
in modern font rendering systems like TrueType and OpenType fonts.
4. 3D Character Generation
- Description: In 3D
character generation, characters are represented as 3D models. Each
character has depth and can be rendered with lighting, shadows, and
textures for more realistic effects.
- Process: The
character model is constructed with polygons or curves, and rendering
techniques like shading and texturing are applied.
- Advantages:
- Provides a more immersive and realistic look
for applications like games and animations.
- Can be rotated and viewed from different
angles.
- Disadvantages:
- High computational cost, requiring
significant processing power and memory.
- Application:
Commonly used in video games, virtual reality applications, and 3D
animation software.
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