Topic 1e
Compression Methods

Learning Outcomes

By the end of this topic students should be able to:

  • Define [Lossy | Lossless] compression.
  • Explain the difference between Lossy/Lossless compression.
  • Give an example of a Lossy Compression technique and how it works.
  • Give an example of a Lossless Compression technique and how it works.
  • Given a description of a compression technique, explain if it is lossy or lossless.

 

Learning Materials

  • Readings
    • Section 1.9 - pp 77-83
  • Videos
    • Crash Course Computing #21 - Compression
      • Note: This video is much later in the actual Crash Course series and therefore will make reference to some videos you haven't watched yet.  However, you should be able to follow the main ideas.
    • Code.org video about Compression featuring Aloe Blacc (you may not know his name, but you may recognize some of his music).
    • Dr. Schafer explains
      • Compression of text
        • Note, there is a typo in my slide at about the 2:26 mark.
        • The bit/ASCII encoding for a space is 00100000
          • Five 0s after the 1
        • I didn't notice that I only had seven of the eight bits there.
      • Compression of pictures
  • Activity

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Checking for Understanding

  • You are welcome to consider the Q&E problems on page 83. However, these do not align with our learning outcomes so do not use a failure as meaning you are in trouble.
  • Give an example of a lossless compression technique (either specific or generic). Explain how it works and why it is a lossless technique.
  • Give an example of a lossy compression technique (either specific or generic). Explain how it works and why we don't care that it is lossy.

 

Additional Guidance

If you are still struggling with the material in this topic, the following video may help.

  • NA

Further Information

  • This goes well beyond what you need to know about compression for this class, but this article/tool can help you explore and, maybe, better understand, how compression works for jpegs. Try out a few of their suggestions for changes to explore the system.