| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Computer Science |
| Lesson Topic: Show understanding of how a text file, bitmap image, vector graphic and sound file can be compressed |
Learning Objective/s:
- Describe the difference between lossless and lossy compression and give typical examples for text, images, vectors and audio.
- Explain how redundancy is exploited in each file type (e.g., character frequency, pixel similarity, geometric description, audio prediction).
- Apply basic steps of Huffman coding, JPEG DCT, and MP3 psycho‑acoustic compression to simple data.
- Calculate compression ratio and average bits per symbol for provided examples.
- Compare the effectiveness of different compression methods across the four media types.
|
Materials Needed:
- Projector and screen
- Whiteboard and markers
- Laptop with demo software (ZIP, PNG, JPEG, FLAC/MP3)
- Handouts summarising algorithms and sample data
- Sample files: plain‑text, bitmap PNG, SVG, WAV
- Worksheets for compression‑ratio calculations
|
Introduction:
Begin with a quick poll: “What happens when you email a photo versus a document?” Use the responses to highlight why file size matters. Review briefly how data is stored (bits, bytes) and set the success criteria: students will be able to explain and compare compression techniques for four media types.
|
Lesson Structure:
- Do‑Now (5'): Students calculate the size of a 100‑character ASCII file and discuss obvious redundancies.
- Mini‑lecture (10'): Overview of lossless vs. lossy concepts with real‑world examples.
- Guided practice (15'): Demonstrate Huffman coding on a short text, then have pupils complete a worksheet on building the tree.
- Interactive demo (12'): Show JPEG compression steps on a sample image; students identify each stage on a flowchart.
- Vector & audio focus (10'): Quick walkthrough of SVG‑GZIP and MP3 psycho‑acoustic model using visual aids.
- Comparison activity (8'): In groups, fill a table comparing compression ratio, lossiness, and typical use for each file type.
- Check for understanding (5'): Exit‑ticket – “State one key idea that makes lossless compression possible for text and one for audio.”
|
Conclusion:
Recap the main ideas: redundancy exploitation, lossless vs. lossy, and how different media lend themselves to specific techniques. Collect exit‑tickets and clarify any misconceptions. Assign homework: students compress a personal file using a free tool and report the ratio and whether any quality loss is noticeable.
|