Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Computer Science
Lesson Topic: Understand how and why a computer represents an image, including the effects of the resolution and colour depth
Learning Objective/s:
  • Describe how digital images are composed of pixels and define resolution.
  • Explain colour depth (bits per pixel) and its impact on colour palette and file size.
  • Calculate the uncompressed size of an image using resolution and colour depth.
  • Analyse how changing resolution or colour depth affects image quality and storage requirements.
  • Compare lossless and lossy compression methods for images.
Materials Needed:
  • Projector or interactive whiteboard
  • Slide deck with pixel‑grid diagram
  • Sample image files of varying resolutions and colour depths
  • Worksheets with calculation exercises
  • Calculators
  • Computers with basic image‑editing software (e.g., Paint, GIMP)
 Introduction:
Begin with a quick poll: how many pixels do students think a typical smartphone photo contains. Review prior learning about binary data and how computers store information. State that today’s success criteria are to describe pixels, resolution, colour depth, calculate file sizes, and evaluate image‑quality choices.
Lesson Structure:
  1. Do‑now (5') – Students answer the poll question on image size and share responses.
  2. Mini‑lecture (10') – Explain pixels, resolution, and colour depth using a diagram.
  3. Guided calculation (10') – Work through the 800 × 600 px @24 bpp example; students compute file size.
  4. Exploration activity (15') – In pairs, adjust resolution and colour depth of sample images in software, observe quality and file size, record findings.
  5. Compression discussion (5') – Brief overview of lossless (PNG) vs lossy (JPEG) compression with visual examples.
  6. Practice questions (10') – Students complete worksheet problems individually while teacher circulates.
  7. Check for understanding (5') – Quick exit‑ticket quiz with one calculation and one conceptual question.
Conclusion:
Summarise that image quality depends on resolution and colour depth, which directly influence file size. Students complete an exit ticket noting one key trade‑off and receive a homework task to research real‑world image requirements for web versus print contexts.