Data compression

• Why are files compressed (2)

  • to reduce storage requirements
  • to make it quicker to transfer files
• What is compression


  The process of reducing the number of bits required to represent data, so that the files take up less memory
• What are the two types of compression

  • lossy compression
  • lossless compression
• What is lossy compression

  Compression in which some of the data is removed, to lower the size of the file and ensure quicker transmission whilst still creating an acceptable representation of the original data
• What are the advantages of lossy compression (3)

  • small file size
  • ideal for web use and mobile data transmission
  • supported by lots of software
• What are the disadvantages of lossy compression (1)

  • Lower quality due to loss of data from higher rate of compression
• What is lossless compression

  Shrinks the file w/o losing important data by rewriting
• what is run-length encoding (RLE)

  a method of compressing data by eliminating repeated data

  • x pixels are y colour = xy
• What is dictionary-based encoding

  A method of compressing text files by eliminating repeated strings of characters
• What are the advantages of lossless compression (2)

  • no loss in quality -> good for text files
  • slight decrease in file size
• What are the disadvantages of lossless compression (1)

  • lossless files are larger than lossy files