What is Lossless?
Definition
Lossless compression shrinks a file without discarding any data, so the original can be rebuilt bit-for-bit with zero quality loss. Examples: FLAC, ALAC, and WAV for audio, and PNG for images.
Lossless compression shrinks files by storing the same data more efficiently - finding patterns and redundancy and encoding them compactly - rather than throwing anything away. When you decompress the file, you get back an exact, byte-identical copy of the original. Nothing is approximated or rounded off, which is why lossless is the standard for archiving, mastering, and any workflow where fidelity must be preserved.
The trade-off is size. Because no information is removed, lossless files stay large: a lossless audio track is often 3-6x bigger than an equivalent MP3, and a PNG is usually larger than a JPEG of the same photo. This is the opposite of lossy compression (MP3, AAC, H.264, JPEG), which permanently deletes detail your senses are less likely to notice in exchange for much smaller files.
A common confusion is thinking a high bitrate means lossless - it does not. A 320 kbps MP3 is still lossy; it has simply discarded less. Another is assuming WAV is 'better' than FLAC: both are lossless audio, but FLAC is compressed (smaller) while WAV/PCM is uncompressed, so they decode to identical audio.
Quick facts
- The original is reconstructed bit-for-bit, with zero quality loss
- Common formats: FLAC, ALAC, WAV/PCM (audio); PNG (images)
- Files are larger than lossy equivalents like MP3 or JPEG
- Opposite of lossy compression (MP3, AAC, H.264, JPEG), which permanently discards data
- Used for archiving, mastering, and editing where fidelity matters