---
title: "Time to scan one row of pixels"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:row-scan-time-refresh"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/row-scan-time-refresh
site: BCT Engineering
---

# Time to scan one row of pixels

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2070 Chaitra, 4 marks
- Video: [SCREEN RESOLUTION -PROBLEM SOLVING](https://www.youtube.com/watch?v=KaoyRUE-BuM) — Namitha Ramachandran
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/row-scan-time-refresh
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

How much time is spent scanning across each row of pixels during screen refresh on a raster system with resolution 1024×768 and a refresh rate of 60 frames per second?

## Short answer

Frame time = 1/60 s. With 768 rows (ignoring retrace), time per row = (1/60)/768 ≈ 21.7 µs.

## Answer

Time for one frame = 1 / 60 s = 16.667 ms. This time is shared among 768 rows (ignoring horizontal and vertical retrace time).

```text
Time per row = (1/60) / 768
             = 1 / 46,080 s
             = 2.17 × 10⁻⁵ s ≈ 21.7 µs
```

**Answer: about 21.7 µs per row of pixels.**

## Check yourself

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

1. What is the time for one frame at 60 fps?
   A. 60 ms
   B. 1/768 s
   C. 1/1024 s
   D. 1/60 s = 16.67 ms
   Answer: D. Frame time is the reciprocal of refresh rate. (Key point: Frame time)

2. Over how many rows is the frame time divided?
   A. 768
   B. 1024
   C. 60
   D. 786,432
   Answer: A. The vertical resolution (rows) is 768. (Key point: Sharing)

3. What is the time per row?
   A. About 16.7 ms
   B. About 21.7 us
   C. About 21.7 ns
   D. About 13 us
   Answer: B. (1/60)/768 = 2.17 x 10^-5 s. (Key point: Row time)

4. What does the calculation ignore?
   A. The number of rows
   B. The refresh rate
   C. Horizontal and vertical retrace time
   D. The resolution
   Answer: C. Retrace is ignored. (Key point: Assumption)

## Related in Computer Graphics

- [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
- [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
- [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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