---
title: "Short note: Raster scan display"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:short-note-raster-scan-display"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/short-note-raster-scan-display
site: BCT Engineering
---

# Short note: Raster scan display

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2072 Kartik, 5 marks
- Video: [Raster Scan Display Explained in Hindi | Computer Graphics (CG) @GateSmashers](https://www.youtube.com/watch?v=47vz2MMvRcs) — Gate Smashers
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/short-note-raster-scan-display
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

Write a short note on raster scan display.

## Short answer

A raster scan display sweeps the electron beam row by row across the screen, using a frame buffer to store pixel intensities. The video controller reads and displays each pixel, refreshing 50–60 Hz. It supports realistic shading and colour but requires large memory and can produce jagged lines.

## Answer

A **raster scan display** shows a picture by sweeping the electron beam across the screen one row (scan line) at a time, from top to bottom, and turning the beam intensity on or off at each pixel according to the frame buffer.

```text
 ->->->->->->->->->|   scan line 1
 <-- horizontal retrace
 ->->->->->->->->->|   scan line 2
   ...
 ^ vertical retrace back to top after last line
```

**Working**
- The image is stored in the **frame buffer** as pixel intensity values (1 bit per pixel for monochrome, 8 to 24 bits for colour).
- The **video controller** reads the frame buffer line by line and drives the beam intensity.
- Screen is refreshed 50 to 60 times per second. The beam is off during horizontal and vertical retrace.
- Scanning may be **interlaced** (odd lines, then even lines) to reduce flicker, or **non-interlaced**.

**Features**
- Realistic images, shading, many colours and filled areas.
- Refresh time is independent of picture complexity.
- Needs large memory; lines appear jagged (aliasing).
- Used in TV, monitors and most modern displays.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does a raster scan display form the picture?
   A. Beam jumps between line endpoints
   B. Beam draws only the lines
   C. Beam sweeps row by row, with intensity set from the frame buffer
   D. Pixels are lit randomly
   Answer: C. The video controller reads the frame buffer line by line. (Key point: Working)

2. What happens to the beam during retrace?
   A. It is at full intensity
   B. It doubles speed
   C. It draws a line
   D. It is off
   Answer: D. Beam is off during horizontal and vertical retrace. (Key point: Retrace)

3. What is interlaced scanning?
   A. Odd lines then even lines, to reduce flicker
   B. Scanning right to left
   C. Scanning only the picture
   D. Using two frame buffers
   Answer: A. Interlacing reduces flicker. (Key point: Interlacing)

4. How does refresh time depend on picture complexity?
   A. It grows with lines
   B. It is independent of it
   C. It halves
   D. It depends on colours
   Answer: B. Raster refresh is fixed. (Key point: Refresh)

## Related in Computer Graphics

- [Random scan versus raster scan display](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Arandom-vs-raster-display) — Computer Graphics, chapter 1, asked 7×
- [Raster display and frame buffer load time](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Araster-system-load-time) — Computer Graphics, chapter 1
- [Pixel access rate of raster system](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Apixels-per-second-access-time) — Computer Graphics, chapter 1