---
title: "Frame buffer for 640×480 B/W video"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:frame-buffer-bw-video-5min"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/frame-buffer-bw-video-5min
site: BCT Engineering
---

# Frame buffer for 640×480 B/W video

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2073 Chaitra, 4 marks
- Video: [Frame buffer in computer graphics(numerical)](https://www.youtube.com/watch?v=I8MByKWmVes) — IT-TECHIEZ
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/frame-buffer-bw-video-5min
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

Calculate the size of frame buffer required to store a 640×480 B and W video of length 5 minutes without compression.

## Short answer

Black‑and‑white uses 1 bit/pixel, so one 640×480 frame = 38,400 bytes. At 25 fps, 5 minutes yields 7,500 frames, giving total storage = 288,000,000 bytes ≈ 275 MB.

## Answer

A black-and-white (bi-level) image needs 1 bit per pixel. The video size equals frame size × number of frames. The frame rate is not given, so assume 25 fps.

```text
Pixels per frame = 640 × 480      = 307,200
Bits per frame   = 307,200 × 1    = 307,200 bits
Bytes per frame  = 307,200 / 8    = 38,400 B (37.5 KB)
Time             = 5 × 60         = 300 s
Frames           = 25 × 300       = 7,500
Total size       = 38,400 × 7,500 = 288,000,000 bytes
                                  ≈ 274.7 MB (÷ 2²⁰)
```

For other frame rates the size scales linearly (at 30 fps: 345,600,000 B ≈ 329.6 MB).

**Answer: one frame needs 38,400 bytes; 5 minutes at 25 fps needs 288,000,000 bytes ≈ 275 MB.**

## Check yourself

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

1. How many bits per pixel does a B and W (bi-level) image need?
   A. 8
   B. 4
   C. 24
   D. 1
   Answer: D. Bi-level means two states, 1 bit. (Key point: Bits per pixel)

2. What is one 640 x 480 B&W frame in bytes?
   A. 38,400
   B. 307,200
   C. 4,800
   D. 76,800
   Answer: A. 307,200 bits / 8 = 38,400 bytes. (Key point: Frame size)

3. Frame rate is not given; with 25 fps assumed, how many frames in 5 minutes?
   A. 1,500
   B. 7,500
   C. 750
   D. 300
   Answer: B. 25 x 300 s = 7,500. (Key point: Frame count)

4. What is the total size at 25 fps?
   A. 38,400 bytes
   B. 28,800,000 bytes
   C. 288,000,000 bytes (about 275 MB)
   D. 2,304,000,000 bytes
   Answer: C. 38,400 x 7,500 = 288,000,000. (Key point: Total size)

## Related in Computer Graphics

- [Frame buffer size for 1 min video](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aframe-buffer-1min-video) — Computer Graphics, chapter 1, asked 2×
- [Memory for 10 minute SVGA video](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aframe-buffer-svga-10min) — Computer Graphics, chapter 1, asked 2×
- [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

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