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      Comparing compression algorithms

      Lesson details

      Learning outcome

      I can compare the suitability of different compression algorithms.

      Key learning points

      1. Different compression algorithms achieve the same goals in different ways.
      2. Compression methods can be compared based on file size reduction, (de)compression speed, and compressed data quality.
      3. The best compression method depends on the intended application, acceptable processing time and desired quality.

      Keywords

      • Algorithm - a set of step-by-step instructions to solve a problem

      • Efficiency - how effectively compression reduces the size of data while maintaining its usability

      • Trade-off - accepting a limitation to achieve a beneficial outcome

      Common misconception

      The best compression method is the one that makes files the smallest.

      Smaller isn’t always better, sometimes important details are lost. The best method depends on the file type, quality needs, and purpose.

      Teacher tip

      Encourage students to think about the type of data being compressed and what's important before choosing a compression method.

      Licence

      This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0
      except where otherwise stated. See Oak's terms & conditions
      (Collection 2).

      Lesson video

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      Prior knowledge starter quiz

      6 Questions

      Q1.
      What does encoding mean in data compression?

      deleting redundant data
      encrypting data
      increasing file size
      Correct answer: changing data into a different format

      Q2.
      What is used to visually represent the encoding scheme in Huffman coding?

      Correct Answer: Huffman tree, tree, a tree

      Q3.
      What lossless compression technique reduces file size by encoding repeating sequences of data?

      Correct Answer: run length encoding, RLE

      Q4.
      What term describes repeated or extra data that can be removed without losing essential meaning?

      Correct Answer: redundancy, redundant data

      Q5.
      What is run length encoding?

      Correct answer: a type of lossless compression
      a type of lossy compression
      a method to increase file size
      a way to encrypt data

      Q6.
      What is the main goal of Huffman coding?

      to delete redundant data
      to increase file size
      Correct answer: to assign shorter bit sequences to more frequent characters
      to create repeating sequences

      6 Questions

      Q1.
      Match each term to its definition.

      Correct Answer:algorithm,a set of step-by-step instructions to perform a task
      Correct Answer:efficiency,how effectively compression reduces file size while ensuring usability
      Correct Answer:trade-off,the limitations and choices faced when optimising competing factors
      Correct Answer:compression speed,how quickly data can be compressed or decompressed

      Q2.
      Why is compression efficiency important?

      Correct answer: It balances file size reduction with usability.
      It deletes redundant data.
      It encrypts files.
      It increases file size.

      Q3.
      What does compression speed refer to?

      how small the file becomes
      how much data is deleted
      how large the original file is
      Correct answer: how quickly data can be compressed or decompressed

      Q4.
      Why isn’t the smallest file size always the best result for compression?

      Smaller files take longer to compress.
      Correct answer: Smaller files might lose important details.
      Smaller files are harder to share.
      Smaller files are less secure.

      Q5.
      What is a limitation of some compression methods?

      They always make files larger.
      They always delete important data.
      Correct answer: They may reduce quality.
      They cannot be used for images.

      Q6.
      Put these steps in order for comparing compression methods:

      1 - Identify the file type.
      2 - Determine the quality requirements.
      3 - Compare the speeds of different methods and the resulting file sizes expected.
      4 - Select the best method.

      To help you plan your 10 computer science lesson on: Comparing compression algorithms, download all teaching resources for free and adapt to suit your pupils' needs...