Lesson Plan

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Lesson Plan
Grade: Date: 25/02/2026
Subject: Computer Science
Lesson Topic: Show understanding of the effects of changing elements of a bitmap image on the image quality and file size
Learning Objective/s:
  • Describe how resolution, colour depth, compression, and file format influence bitmap image quality and file size.
  • Calculate the approximate uncompressed size of a bitmap given its dimensions and colour depth.
  • Compare lossless and lossy compression methods and predict their impact on visual quality.
  • Evaluate which file format best suits a specific use‑case based on quality and size requirements.
Materials Needed:
  • Projector and screen
  • Computer with image‑editing software (e.g., GIMP or Photoshop)
  • Sample bitmap images (BMP, PNG, JPEG)
  • Worksheet with calculation tasks and scenario questions
  • Printed handout of the summary table
  • Whiteboard and markers
 Introduction:

Begin with a quick poll: “Which image format do you see most often online?” Use this to link everyday experience to the need for balancing quality and file size. Review prior knowledge of pixels, colour depth, and basic compression concepts. Explain that by the end of the lesson students will be able to analyse and choose the optimal bitmap settings for a given purpose.
Lesson Structure:
  1. Do‑now (5'): Short quiz on definitions of resolution, colour depth, and compression.
  2. Mini‑lecture (10'): Explain each bitmap element with formulas and the summary table; highlight real‑world examples.
  3. Guided calculation activity (12'): Students work in pairs to compute file sizes for a 800 × 600 px image at 24‑bit and 8‑bit depths using the worksheet.
  4. Compression demo (10'): Using the image editor, save the same image as BMP, PNG, and JPEG; record size and visual differences.
  5. Group discussion (8'): Evaluate which format is best for web, print, and archival scenarios.
  6. Exit ticket (5'): Individually write one recommendation for choosing a bitmap format based on a provided scenario.
Conclusion:

Recap the key trade‑offs between resolution, colour depth, compression type, and file format. Collect exit tickets to gauge understanding and address any lingering misconceptions. For homework, ask students to locate an online image, note its format and size, then recreate it with at least two different settings and compare the outcomes.