Raster Scan Display
A Raster Scan Display
is a display technology where the electron beam sweeps across the screen line
by line from top to bottom (like reading a page), illuminating pixels based on
intensity values stored in a frame buffer. The image is formed by this
systematic scanning pattern, refreshed many times per second (typically 60–80
Hz) to maintain a stable picture.
Components of Raster Scan
Display (Based on the Diagram)
1. CPU (Central
Processing Unit) The brain of the system. It generates and
sends display commands and interaction data to coordinate the entire display
process.
2. I/O Port
Acts as the communication interface between the CPU and the display system. It
passes interaction data and display commands to the Display Controller.
3. System Memory
Stores the data and programs needed for rendering. It feeds information to the
Display Controller for processing.
4. Display Controller
The central coordinator of the display pipeline. It receives display commands
and interaction data, then manages the flow of image data from memory to the
screen.
5. Display Processor /
Graphics Controller Also called the Display Co-Processor. It
handles graphical computations like scan conversion (converting geometric
shapes into pixel data), transformations, and clipping — offloading this work
from the CPU.
6. Frame Buffer (Refresh
Buffer Memory) A special memory that stores the pixel
intensity values of the entire screen. In the diagram, it is shown with binary
pixel data (00000, 01110, etc.). It continuously feeds the Video Controller
with pixel data for each refresh cycle. For a colored image of 24-bit depth (as
noted in the diagram), each pixel uses 8 bits each for red, green, and blue
channels (values 0–255).
7. Video Controller
Reads pixel data from the Frame Buffer row by row and converts it into analog
voltage signals to drive the CRT. It controls timing and synchronization of the
scan.
8. CRT (Cathode Ray Tube)
The actual display device (shown as "T" in the diagram). The electron
gun inside the CRT fires beams based on the signals from the Video Controller,
lighting up phosphor dots on the screen to form the visible image.
9. Display Processor
Memory Dedicated memory for the Display Processor to store
intermediate graphical data, display lists, and instructions during processing.
10. Color Image — 24-bit
(RGB) As shown in the top-right of the diagram, a color
pixel is represented using 24 bits split into three 8-bit channels — Red
(0–255), Green (0–255), and Blue (0–255). This gives 256³ ≈ 16.7 million
possible colors.
Figure: Raster Scan Display
Working Procedure of Raster Scan Display
Step 1 — Scene Definition:
The CPU defines the scene geometry and sends display commands through the I/O
Port to the Display Controller.
Step 2 — Scan Conversion:
The Display Processor/Graphics Controller performs scan conversion, translating
vector/geometric objects into discrete pixel intensity values (this is why
"Scan Conversion" is labeled in the diagram).
Step 3 — Frame Buffer Storage:
The computed pixel intensity values are stored in the Frame Buffer (Refresh
Buffer Memory) as a 2D array of pixel data. For a 24-bit color image, each
pixel stores R, G, B values independently.
Step 4 — Video Scanning:
The Video Controller reads the Frame Buffer row by row, 60–80 times per second.
For each row (scan line), it sends the pixel data as analog signals to the CRT.
Step 5 — Electron Beam Sweep:
Inside the CRT, the electron beam sweeps horizontally from left to right across
each scan line, then retraces (horizontal retrace) to the start of the next
line. After completing all lines, it returns to the top-left (vertical retrace)
and the process repeats — this is the raster scan pattern.
Step 6 — Image Display:
Phosphor dots on the CRT screen glow with appropriate intensity/color when
struck by the electron beam, forming the visible image. Continuous refreshing
prevents flicker.
Applications of Raster Scan Display
1. Television and Broadcasting
Raster scan is the fundamental technology behind
traditional CRT televisions and modern digital TVs. The entire broadcast signal
is structured around raster scanning principles, where each video frame is
transmitted as a series of horizontal scan lines. Standard definition TV uses
525 lines (NTSC) while HD systems use 720 or 1080 lines per frame.
2. Computer Monitors and Desktop Displays
All modern computer monitors — whether LCD, LED, OLED,
or older CRT — operate on raster scan principles. The graphics card stores the
frame in a buffer and the display refreshes it continuously at rates of 60Hz,
144Hz, or higher for gaming monitors. Every application you see on screen, from
text editors to web browsers, is rendered as a raster image.
3. Medical Imaging Systems
Raster scan displays are extensively used in medical
equipment such as CT scan viewers, MRI display workstations, ultrasound
monitors, and digital X-ray systems. The ability to display grayscale gradients
and color-coded intensity maps makes raster displays ideal for visualizing soft
tissue, bone density, and blood flow in real time.
4. Geographic Information Systems (GIS)
and Satellite Imaging
Satellite images, aerial photographs, topographic
maps, and weather radar outputs are all raster-based. Applications like Google
Earth, weather forecasting software, and remote sensing tools rely on raster
scan display to render pixel-by-pixel geographic and atmospheric data on
screen.
5. Video Games and Gaming Consoles
Modern gaming is entirely built on raster scan
technology. Game engines render complex 3D scenes by converting geometry into
pixel data stored in frame buffers, which are then displayed via raster
scanning. High refresh rate displays (144Hz, 240Hz) and technologies like
V-Sync and G-Sync are direct extensions of raster scan display management.
6. Digital Photography and Image Editing
Applications like Adobe Photoshop, GIMP, and Lightroom
work exclusively with raster images. Digital cameras capture scenes as pixel
arrays and display them on raster screens. Every photo you view, crop, or
color-correct is a raster image rendered through raster scan display
technology.
7. Surveillance and Security Systems
(CCTV)
Security cameras capture video as a continuous raster
image stream. CCTV monitoring stations display multiple camera feeds
simultaneously on raster scan monitors. Video recording systems store footage
as raster frame sequences, enabling frame-by-frame playback and analysis.
8. Air Traffic Control and Radar Systems
Modern radar displays use raster scan technology to
show aircraft positions, flight paths, weather patterns, and airspace
boundaries. The continuous refresh capability of raster displays ensures
real-time tracking of moving targets. Color-coded raster displays distinguish
between different aircraft altitudes and weather intensities.
9. Scientific Visualization and Simulation
Fields like physics, chemistry, astronomy, and
engineering use raster displays to visualize complex simulations — fluid
dynamics, molecular modeling, climate simulations, and finite element analysis.
These applications require dense pixel grids to represent fine-grained data
gradients and color maps accurately.
10. Digital Cinema and Video Production
Movie theaters now use digital projectors that work on
raster scan principles, projecting frames at 24, 48, or 60 frames per second.
Video editing software (Adobe Premiere, DaVinci Resolve) uses raster scan
displays to preview footage, apply color grading, and composite visual effects
frame by frame.
11. Smartphones and Tablet Displays
Every smartphone and tablet screen — AMOLED, IPS LCD,
or Retina — operates on raster principles. The display controller refreshes
pixel arrays at 60–120Hz. All apps, videos, images, and UI elements are
rendered as raster images on these high-resolution screens.
12. Virtual Reality (VR) and Augmented
Reality (AR)
VR headsets like Oculus and HTC Vive use
high-resolution raster scan displays (one per eye) refreshed at 90Hz or higher
to create immersive environments. The frame buffer must be updated extremely
rapidly to prevent motion sickness. AR glasses overlay raster-rendered digital
content onto the real-world view.
13. Digital Signage and Advertising Boards
Large LED billboards, airport information displays,
stadium scoreboards, and retail digital signage all use raster scan display
technology. Content is managed as pixel-mapped raster images and video streams
that are refreshed continuously across massive display arrays.
14. Industrial and Process Control
Displays
Manufacturing plants, power stations, and chemical
plants use raster scan HMI (Human Machine Interface) displays to monitor
equipment status, sensor readings, process flow diagrams, and alarm conditions.
Color-coded raster graphics make it easy for operators to identify abnormal
states quickly.
Raster Scan Display vs Vector Scan Display
|
Feature |
Raster Scan Display |
Vector Scan Display |
|
Scanning Method |
Electron beam scans line by line across entire
screen |
Electron beam is directed only to specific
points/lines where drawing is needed |
|
Image Representation |
Image stored as pixel array in Frame Buffer |
Image stored as a list of drawing commands (display
list) |
|
Picture Quality |
Slightly jagged edges (aliasing effect) due to pixel
grid |
Smooth, sharp lines as beam draws directly |
|
Color & Shading |
Excellent support for color, shading, and realistic
images |
Limited color and shading capability |
|
Complexity of Images |
Handles complex, filled, photorealistic images well |
Best for line drawings and simple vector graphics |
|
Memory |
Requires large Frame Buffer memory (e.g., 24-bit ×
screen resolution) |
Requires less memory; only stores geometric commands |
|
Refresh |
Entire screen refreshed at fixed rate regardless of
image complexity |
Refresh time depends on the number of objects;
complex scenes cause flicker |
|
Resolution |
Fixed resolution determined by pixel grid |
Resolution-independent; lines remain smooth at any
scale |
|
Cost |
Less expensive; widely used in modern displays |
More expensive; used in specific applications like
oscilloscopes, early CAD |
|
Applications |
TVs, monitors, smartphones, modern graphics systems |
Old CAD terminals, radar displays, flight simulators |
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