There are two types of compression: lossy (which permanently removes some data to achieve smaller file sizes) and lossless (which compresses without losing any data). Each is suited to different applications.
Key points
Definition:Lossy Compression: permanently removes some data to reduce file size. Quality is reduced and the original file CANNOT be fully restored.
Definition:Lossless Compression: reduces file size without losing any data. The original file CAN be fully restored.
Lossy is used for: images, audio, video — where slight quality loss is acceptable for much smaller files.
Lossless is used for: text files, program files, medical images — where NO data can be lost.
Lossy achieves GREATER file size reduction than lossless.
Exam Tip:If asked which type is suitable, consider whether data loss is acceptable. For text/code = lossless (every character matters). For media = lossy (small quality loss is OK).
Common Mistake:Saying lossless 'doesn't compress as much'. It is still effective — it just does not reduce size as dramatically as lossy.
Exam Tip:For text files, you MUST use lossless — lossy cannot be applied to text files because removing data would corrupt the file/make it unreadable.
Exam Tip:When justifying lossy for images, say: 'lossy reduces the file size by the largest amount AND the changes are unlikely to be noticed by the user'.
Common Mistake:Just saying 'lossy compresses the file more'. That repeats the question. Explain what this MEANS — e.g. 'reduces file size significantly because it permanently removes unnoticeable data'.