Lossless vs lossy compression

Every compressed file format makes a choice: preserve every bit of the original data exactly, or discard some data to achieve a smaller file. This is the lossless vs. lossy tradeoff, and it applies to every media type — images, audio, video, and documents.

Lossless compression reduces file size without discarding any data. When you decompress a lossless file, you get back the exact original. Examples: PNG, WebP lossless, FLAC, WAV, ZIP, TAR.

Lossy compression achieves much smaller files by discarding data that human perception is least sensitive to. The discarded data cannot be recovered — the loss is permanent. Examples: JPG, WebP lossy, MP3, OGG Vorbis, MP4 (H.264), AVI (DivX).

Lossy → lossless doesn't improve quality. Converting a JPG to PNG doesn't restore quality lost during JPG compression. The PNG is larger but contains the same artifact-laden image. This is the most common misconception in file conversion.

Lossy → lossy introduces generation loss. Every time you convert between two lossy formats (MP3 → OGG, JPG → JPG, AVI → MP4), you lose quality twice. Start from a lossless source when possible — WAV or FLAC for audio, PNG for images.

Lossless → lossy is always a one-way trip. Once you encode a WAV to MP3 or a PNG to JPG, the discarded data is gone permanently. Keep your lossless originals.

For archiving, always use lossless. PNG for images, FLAC for audio, the original video master. Use lossy formats for distribution and consumption copies.