Glossary / Lossless vs Lossy Compression
Lossless vs Lossy Compression
Lossless compression reduces file size while preserving all original data exactly, so the file can be perfectly reconstructed. Lossy compression achieves much smaller file sizes by permanently discarding some data that is considered less perceptible to humans.
How they differ
Lossless algorithms like Flate/Deflate (used in PNG and PDF content streams), LZW, and Brotli find patterns in data and encode them more efficiently. The decompressed output is bit-for-bit identical to the original. Typical lossless compression ratios range from 2:1 to 10:1.
Lossy algorithms like JPEG and WebP (lossy mode) analyze human perception to discard information the eye is unlikely to notice. This allows compression ratios of 10:1 to 100:1 or more, but the original data cannot be recovered once compressed.
When to use each
Use lossless for text documents, technical diagrams, screenshots, logos, and any content where every detail matters. Use lossy for photographs, scanned documents, and media where a slight quality reduction is acceptable in exchange for significantly smaller files.
Related tools on fixtdoc
- Compress PDF , choose quality levels from lossless to high compression
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