Cambridge O Level Computer Science · Syllabus 2210 · Data Representation
Lossy Compression
What is Lossy Compression?
Lossy compression reduces the file size by permanently removing data, so the original file cannot be reconstructed exactly and quality may be reduced.
This definition is part of the Data Representation chapter in Cambridge O Level Computer Science.
Lossy Compression in context
Lossy compression reduces the file size by permanently removing data. The original cannot be reconstructed exactly, and quality may fall — the more the file is compressed, the more noticeable that loss becomes. Lossless compression reduces the file size without permanently losing any data, so the original can be reconstructed exactly. Run-length encoding is the syllabus example of a lossless method.
Common mistakes with Lossy Compression
- M20. "Lossy compression can always recreate the original." Why it fails Lossy removes data permanently. Decompression can only redistribute what survived. Correct model Lossy gives back an approximation; only lossless gives back the exact original. Exam-safe "Lossy compression permanently removes data, so the original file cannot be reconstructed exactly." Test yourselfHideQ. Which method must be used for a program file, and why?A. Lossless, because the file must be reconstructed exactly or it will not run correctly.
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