Lesson Plan

• Describe why image compression is essential for storage and transmission.
• Differentiate lossless and lossy compression techniques and their typical file formats.
• Calculate compression ratios and interpret their effect on image quality and file size.
• Evaluate which compression method best suits a given image type or use‑case.

• Projector and computer with internet access
• Sample images (photograph and line‑art) in original format
• Image editing software (e.g., GIMP, Photoshop) or online converters
• Simple RLE script or spreadsheet for compression demo
• Worksheet for calculations and recording file sizes
• Calculators (or calculator function on computers)

Begin with a quick poll: “How many megabytes does a typical smartphone photo use?” Use the responses to highlight the challenge of storing and sharing large images. Connect to prior knowledge of file size and ask students to predict what happens when we try to upload such files on a slow connection. Explain that today they will learn how compression solves this problem and how they will know which method to choose.

1. Do‑now (5'): Quick quiz on data size and why compression matters; discuss answers.
2. Mini‑lecture (10'): Introduce compression ratio, bit depth, redundancy; compare lossless vs lossy concepts.
3. Demonstration (10'): Show PNG vs JPEG of the same photograph, compare file sizes and visual quality on the projector.
4. Hands‑on activity (15'): Students save a provided photograph as PNG and JPEG at three quality settings, record sizes, and note any artefacts.
5. Coding exercise (10'): Use a simple RLE script to compress a bitmap image; compare original and compressed sizes.
6. Calculation practice (10'): Compute compression ratios for the images saved earlier; discuss what the numbers indicate.
7. Whole‑class discussion (5'): Match image types (line art, photo, web graphic) with the most appropriate compression method.
8. Exit ticket (5'): Write one key difference between lossless and lossy and one scenario where each is preferred.

Summarise how compression balances file size against visual quality and reinforce the decision‑making checklist for choosing a format. Collect exit tickets to gauge understanding, then assign a short homework: research an emerging format (e.g., WebP or HEIF) and write a brief comparison with JPEG and PNG.