Learning objective
Data compression: Know why images and sound files are often compressed and that other files, such as text files, can also be compressed. Understand the difference between lossless and lossy compression and explain the advantages and disadvantages of each. Explain the principles behind the following techniques for lossless compression: • run length encoding (RLE) • dictionary-based methods.
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Topic
Representing images, sound and other data
Subtopic
Data compression
Aqa A Level Computer ScienceFundamentals of data representation
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Quick explanation
Data compression: Know why images and sound files are often compressed and that other files, such as text files, can also be compressed. Understand the difference between lossless and lossy compression and explain the advantages and disadvantages of each. Explain the principles behind the following techniques for lossless compression: • run length encoding (RLE) • dictionary-based methods
- This point belongs to Representing images, sound and other data, especially Data compression.
- You need to be able to data compression: Know why images and sound files are often compressed and that other files, such as text files, can also be compressed. Understand the difference between lossless and lossy compression and explain the advantages and disadvantages of each. Explain the principles behind the following techniques for lossless compression: • run length encoding (RLE) • dictionary-based methods.
- Use the linked flashcards and practice questions to check recall, then practise applying the idea in an exam-style answer.
Why it matters
This objective helps connect Data compression to exam-style questions, flashcards, and revision notes for Representing images, sound and other data.
Quick student answer
Why are image and sound files often compressed?
Direct answer
To reduce the amount of storage space and data needed to transmit them
Key terms
- Lossless compression: A compression method that preserves all original data so that the original file can be reconstructed exactly.
- Run length encoding: A lossless compression technique that represents consecutive repeated values by recording the value and the number of repetitions.
Common trap
Confusing lossless and lossy compression: Lossless compression preserves all data and permits exact reconstruction. Lossy compression permanently removes some data, so the exact original cannot be recovered.
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