3.3 Data RepresentationKey Facts

Image File Size Calculation

Part of Images & Sound · GCSE GCSE Computer Science revision

This key facts covers Image File Size Calculation within Images & Sound for GCSE Computer Science. Revise Images & Sound in 3.3 Data Representation for GCSE Computer Science with 18 exam-style questions and 16 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 5 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 5 of 12

Practice

18 questions

Recall

16 flashcards

Image File Size Calculation

Formula:

  File Size (bits) = Width × Height × Color Depth
  File Size (bytes) = (Width × Height × Color Depth) ÷ 8

Example 1: Simple Calculation

  Image: 800 × 600 pixels, 24-bit color depth
  
  Step 1: Calculate total pixels
  800 × 600 = 480,000 pixels
  
  Step 2: Calculate bits
  480,000 pixels × 24 bits = 11,520,000 bits
  
  Step 3: Convert to bytes
  11,520,000 bits ÷ 8 = 1,440,000 bytes
  
  Step 4: Convert to MB (optional)
  1,440,000 bytes ÷ 1,048,576 = 1.37 MB

Example 2: HD Photo

  Image: 1920 × 1080 pixels, 24-bit color depth
  
  1920 × 1080 = 2,073,600 pixels
  2,073,600 × 24 = 49,766,400 bits
  49,766,400 ÷ 8 = 6,220,800 bytes ≈ 6.2 MB

Example 3: Different Color Depths

  Same image (640 × 480 pixels) at different color depths:
  
  1-bit (B&W): 640 × 480 × 1 ÷ 8 = 38,400 bytes (37.5 KB)
  8-bit (256 colors): 640 × 480 × 8 ÷ 8 = 307,200 bytes (300 KB)
  24-bit (True Color): 640 × 480 × 24 ÷ 8 = 921,600 bytes (900 KB)
  
  24-bit is 24× larger than 1-bit!

Keep building this topic

Read this section alongside the surrounding pages in Images & Sound. That gives you the full topic sequence instead of a single isolated revision point.

Image Representation - Bitmap Graphics Bitmap vs Vector Graphics The Digital Camera Trick Image and Sound Data Representation

Practice Questions for Images & Sound

What does colour depth refer to in a digital image?

A. The number of pixels in the image
B. The number of bits used to represent each pixel's colour
C. The physical dimensions of the image in centimetres
D. The number of samples taken per second

1 markfoundation

Explain the effect of increasing colour depth on a digital image. Refer to both file size and image quality in your answer.

3 marksstandard

Quick Recall Flashcards

18 questions on Images & Sound — practise free

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Image Representation - Bitmap Graphics

Bitmap vs Vector Graphics