---
title: "Pixel access rate of raster system"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:pixels-per-second-access-time"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/pixels-per-second-access-time
site: BCT Engineering
---

# Pixel access rate of raster system

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2071 Shrawan, 4 marks
- Video: [How to find refresh rate for frame buffer Computer graphics previous year UGC NET July 2018 solution](https://www.youtube.com/watch?v=5A3MjdjsbW8) — Jyoti Chopra
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/pixels-per-second-access-time
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

Consider a raster scan system having 12 inch by 10 inch screen with a resolution of 100 pixels per inch in each direction. If the display controller of this system refreshes the screen at the rate of 50 frames per second, how many pixels could be accessed per second and what is the access time per pixel of the system?

## Short answer

Pixels per frame = 1200×1000 = 1,200,000. With 50 fps, pixels accessed per second = 60,000,000. Access time per pixel = 1 / 60,000,000 ≈ 16.67 ns.

## Answer

```text
Screen = 12 in × 10 in, 100 pixels/in
Resolution = 1200 × 1000 = 1,200,000 pixels per frame
Refresh rate = 50 frames/s

Pixels accessed per second = 1,200,000 × 50 = 60,000,000
Access time per pixel      = 1 / 60,000,000 s
                           = 1.667 × 10⁻⁸ s = 16.67 ns
```

(Retrace time is ignored.)

**Answer: 6 × 10⁷ pixels per second; access time ≈ 16.67 ns per pixel.**

## Check yourself

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

1. What is the number of pixels per frame for 12 in x 10 in at 100 ppi?
   A. 120,000
   B. 22,000
   C. 12,000,000
   D. 1,200,000
   Answer: D. 1200 x 1000. (Key point: Resolution)

2. How many pixels are accessed per second at 50 fps?
   A. 60,000,000
   B. 1,200,000
   C. 6,000,000
   D. 600,000,000
   Answer: A. 1,200,000 x 50. (Key point: Pixels per second)

3. What is the access time per pixel?
   A. About 1.667 ms
   B. About 16.67 ns
   C. About 16.67 us
   D. About 0.167 ns
   Answer: B. 1 / (6 x 10^7) = 1.667 x 10^-8 s. (Key point: Access time)

4. What does this calculation ignore?
   A. The frame rate
   B. The resolution
   C. Retrace time
   D. Pixel count
   Answer: C. Retrace time is ignored. (Key point: Assumption)

## Related in Computer Graphics

- [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
- [Time to scan one row of pixels](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Arow-scan-time-refresh) — Computer Graphics, chapter 1
- [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×
- [Short note: Raster scan display](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Ashort-note-raster-scan-display) — Computer Graphics, chapter 1
- [Time to display a pixel](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Atime-to-display-pixel) — Computer Graphics, chapter 1

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