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Year 8 · Computing · Binary and data · Lesson 4

Images as data

How images are stored as data: pixels, bitmaps, colour depth, resolution, metadata and calculating image file size.

Whiteboard video lesson: Images as data

19-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

Watch free for a month

What your child will learn

  • Explain pixels and bitmaps
  • Work out colours from colour depth
  • Explain resolution
  • Calculate image file size
  • Explain metadata

The method

  1. Find width and height in pixels.
  2. Find the colour depth.
  3. Multiply width × height × depth.
  4. Divide by 8 for bytes.

Key words: pixel, bitmap, colour depth, resolution, file size, metadata, pixelation.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

What does ‘pixel’ stand for?

  1. Step 1: Picture element

Answer: Picture element

Question 2

In a 1-bit image, what do 1 and 0 usually mean?

  1. Step 1: 1 = black, 0 = white (or the other way)

Answer: Black and white (1 = black, 0 = white)

Question 3

How many colours does 2-bit colour depth give?

  1. Step 1: 2 × 2

Answer: 4