GCSE > Computer Science > Eduqas > GCSE Computer Science > COMPUTER SYSTEMS: Encoding and compression > Compression
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COMPUTER SYSTEMS: Encoding and compression

COMPUTER SYSTEMS: Network topologies

COMPUTER SYSTEMS: Wired and wireless networks, protocols, and layers

COMPUTER SYSTEMS: Threats to computer systems and networks

COMPUTER SYSTEMS: Operating systems and utility software

COMPUTER SYSTEMS: Impact of technology on society

ALGORITHMS AND PROGRAMMING: Types of data

ALGORITHMS AND PROGRAMMING: Producing robust programs

ALGORITHMS AND PROGRAMMING: Designing, creating, and refining algorithms

ALGORITHMS AND PROGRAMMING: Programming languages

ALGORITHMS AND PROGRAMMING: Artificial Intelligence (AI)

  • File compression reduces file size for faster downloads, saving storage, or streaming.
  • Smaller files can load faster and transmit more quickly over networks. However, the trade-offs are that compression can reduce quality. 
  • There are two types of compression: lossy and lossless.
    • Lossy compression: removes data that humans are unlikely to notice (i.e. not visible/audible to our ears/eyes). For example, it may reduce colour detail and simplify areas of similar colour, so is suitable for photographs where perfect accuracy is less important. 
    • Lossless compression: no data is permanently removed and the original image can be perfectly restored. This occurs through:
      • Run-Length Encoding (RLE): replaces repeated pixel values with a count (e.g. 10 red pixels)
      • Dictionary-based compression (e.g. LZW compression algorithm)
Type of compression Lossy Lossless
Quality Some data is lost permanently No data is lost
File size Much smaller Reduced, but not as much as lossy
Use Images (JPEG), music (MP3), video Text, software, images needing full quality
Advantage Saves lots of space Keeps original data exactly
Disadvantage Can’t get original back Less space saved

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