Lossy vs Lossless Compression: What's the Difference?

Compression reduces file size by encoding data more efficiently. The fundamental choice is between lossy compression (some data is permanently discarded) and lossless compression (all original data can be perfectly reconstructed).

Lossy compression achieves much smaller file sizes by discarding information deemed less important. JPG images, MP3 audio, and H.264 video all use lossy compression. The trade-off is irreversible: once you compress a PNG photo to JPG, you cannot recover the discarded detail. For photographs and natural images, lossy compression is ideal because the lost detail is imperceptible at reasonable quality settings.

Lossless compression finds patterns and redundancies in data to represent it more compactly without losing any information. PNG images, FLAC audio, and ZIP archives use lossless compression. The file size reduction is more modest — typically 30–60% for images — but every pixel or byte is preserved exactly.

When to use each: Use lossy for photographs, video, and audio where perfect fidelity isn't required and file size is a priority. Use lossless for logos, screenshots, text, medical images, archival documents, and any content where pixel-perfect accuracy matters. Never edit and re-save a lossy file repeatedly — each save compounds the quality loss. Always keep a lossless master copy.