Compression

Compression

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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