Computer Science · Grade 10

Active learning ideas

Representing Text and Images

Active learning makes abstract concepts concrete for students, which is especially important when teaching how computers represent text and images. By handling binary codes, color values, and file sizes directly, students build mental models that textbooks alone cannot convey.

• Ontario Curriculum Expectations
• CS.HS.D.1
• CS.HS.D.2

• 20–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Inquiry Circle
• 30 min · Pairs

Pairs: ASCII Text Encoder

Pairs receive printed ASCII tables and sample text. They convert each character to 8-bit binary by hand, then verify using an online converter. Finally, they decode a binary string back to text and discuss patterns in bit usage.

Analyze how character encoding schemes like ASCII and Unicode work.

Facilitation Tip

During the ASCII Text Encoder activity, circulate to ensure pairs record both the ASCII lookup and binary conversion for each character to reinforce the connection.

What to look for

Provide students with a short paragraph of text. Ask them to calculate the approximate file size in bytes if it were encoded using ASCII (8-bit). Then, ask them to identify one advantage of using Unicode for this text.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Inquiry Circle
• 45 min · Small Groups

Small Groups: Pixel Color Mixer

Groups use graph paper to create 8x8 pixel art, assigning RGB values (0-255) to each square. They calculate total storage in bytes (3 bytes per pixel) and recreate the image on digital tools like Paint. Compare group artworks for size differences.

Explain how pixels and color models represent images digitally.

Facilitation Tip

For the Pixel Color Mixer, provide a color wheel reference so students can verify RGB values before converting to hex.

What to look for

On an index card, have students draw a 2x2 grid of pixels. Assign a simple RGB value (e.g., R:255, G:0, B:0 for red) to each pixel and ask them to describe the resulting mini-image and its storage requirement in bits.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Inquiry Circle
• 25 min · Whole Class

Whole Class: File Size Challenge

Display images of varying resolutions and color depths. Class predicts uncompressed sizes using formulas (width x height x bit depth / 8). Reveal actual sizes with file properties and vote on most efficient for web use.

Compare the storage requirements for different types of digital media.

Facilitation Tip

In the File Size Challenge, give sample files with different resolutions so groups can see how changing dimensions affects storage.

What to look for

Pose the question: 'Why might a company choose to use a lower resolution image on their website even if it means slightly less visual detail?' Guide students to discuss the trade-offs between image quality, file size, and user experience (loading speed).

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 04

• Inquiry Circle
• 20 min · Individual

Individual: Unicode Explorer

Students pick a non-English phrase and find its Unicode code points online. They note hex values, bit lengths, and compare to ASCII limits. Journal how this supports multilingual apps.

Analyze how character encoding schemes like ASCII and Unicode work.

What to look for

Provide students with a short paragraph of text. Ask them to calculate the approximate file size in bytes if it were encoded using ASCII (8-bit). Then, ask them to identify one advantage of using Unicode for this text.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

A few notes on teaching this unit

Teachers should start with hands-on encoding before explaining theory, letting students discover patterns like how ASCII uses 7 bits for common characters. Avoid diving into compression algorithms too early; focus first on how raw data is represented. Research shows that students grasp binary encoding better when they convert their own names or short messages, which makes the topic personal and memorable.

Successful learning looks like students confidently converting characters to binary, mixing colors to match hex codes, and calculating storage sizes with clear reasoning. They should explain why different encodings matter and justify their choices with evidence from the activities.

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Watch Out for These Misconceptions

• During the ASCII Text Encoder activity, watch for students who assume letters are stored as images of letters.

  Have them build a lookup table where each character is mapped to its ASCII code and binary representation. Ask them to verify that 'B' always maps to 01000010, regardless of how it looks on screen.

• During the Pixel Color Mixer activity, watch for students who think higher resolution always means larger file size.

  Provide a 2x2 pixel image and a 4x4 version of the same image for comparison. Guide them to calculate the storage difference to reinforce that more pixels require more bits.

• During the Unicode Explorer activity, watch for students who believe Unicode uses the same fixed bits per character as ASCII.

  Give them a short English word and a word with accented characters. Have them use an encoding tool to observe how common letters use fewer bits while special characters expand.

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Methods used in this brief

• Inquiry Circle