Topic Five (1.5): Compression
Introduction
In this topic students need to show a good understanding of how digital data can be compressed, using either lossless (including Run Length Encoding (RLE)) or lossy techniques.
By the end of this topic you should be able to:
- Show an understanding of the need for compression and identify examples.
- Show an understanding of lossy and lossless compression and justify the use given a situation.
- Show how different files can be compressed.
Watch
These videos will introduce the 2 types of file compression: lossy and lossless, they will also show you how Run Length Encoding (RLE) compression works.
WATCH – Lossy vs Lossless Compression (YouTube) Links to an external site.
WATCH – How Video Compression Works (YouTube) Links to an external site.
Read and Make Notes
Read pages 21 to 23 of the textbook. Attempt the extension questions on page 23.
Further Reading
READ - Music Compression Algorithms and Why You Should Care (Benjamin, 2010) Download READ - Music Compression Algorithms and Why You Should Care (Benjamin, 2010)
READ - How File Compression Works (HowStuffWorks) Links to an external site.
End of Topic Review
Work through exam style questions 2c and 5c on pages 24 and 25.
You may check your answers using the Module 1 Exam style answer sheet.
Top Tip
- It is vital that a file containing text is compressed using a lossless technique, otherwise the text could become illegible.
- Lossy techniques normally rely on the imperfection of human senses, such as limited ability to hear certain frequency ranges or limited ability to distinguish between colours.