- 2073 Bhadra · 6 marks
Lossless versus lossy compression
Short answer
Lossless compression preserves the original data exactly, with low to moderate ratios (2:1 to 3:1), using statistical redundancy. Lossy compression permanently discards some information, achieving high ratios (10:1 to 100:1) by exploiting human perception limits. Lossless is reversible and used for text/programs; lossy is irreversible and used for photos, music, video.
Differentiate between lossless and lossy data compression.
Lossless compression reduces size so that the decompressed data is identical to the original. Lossy compression discards some information permanently, so the decompressed data is only an approximation of the original.
| Point | Lossless | Lossy |
|---|---|---|
| Data recovery | Exact original is recovered | Only an approximation is recovered |
| Information loss | None | Some detail is lost for good |
| Compression ratio | Low to moderate (about 2:1 to 3:1) | High (10:1 to 100:1 or more) |
| Exploits | Statistical redundancy | Redundancy plus human perception limits |
| Typical media | Text, program files, medical and legal images | Photos, music, video, streaming |
| Techniques | RLE, Huffman, arithmetic, LZW | DCT, quantization, DPCM, vector quantization |
| Reversibility | Fully reversible | Not reversible |
| Examples/formats | ZIP, PNG, GIF, FLAC, TIFF | JPEG, MP3, MPEG, AAC |
| Quality on repeated saving | Unchanged | Degrades each time it is re-compressed |
| Output size | Larger | Much smaller |
Choice: use lossless when every bit matters (a document, an executable), and lossy when small size matters more than perfect fidelity (a streamed video).
✓ Answer checked by Claude Opus 5.5 (high effort)
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