What is Lossless Compression?
Lossless Compression — Lossless compression reduces file size without removing any image data — the original pixel values can be perfectly reconstructed from the compressed file. PNG, GIF, and WebP lossless are the main lossless image formats.
Lossless compression reduces file size by encoding image data more efficiently — finding redundant patterns and representing them with fewer bits — without discarding any data. The decompressed output is a mathematically identical copy of the original input, with every pixel value preserved exactly.
Lossless compression algorithms used in images include: DEFLATE (PNG), LZW (GIF), and the lossless mode of WebP/AVIF. These algorithms work by finding repeated sequences of bytes (run-length encoding, dictionary encoding) and replacing them with shorter codes.
The compression ratio for lossless methods depends heavily on image content. A large area of uniform color (a blue sky, a white background) compresses dramatically; a field of random noise (film grain, sensor noise) compresses barely at all. Lossless compression is typically 2–5× smaller than uncompressed (BMP/TIFF) for photographs, and 3–10× smaller for flat-color graphics.
Lossless Compression in Practice
PNG is the most widely supported lossless format and the standard for images requiring exact pixel fidelity: logos, icons, UI screenshots, pixel art, and medical images. WebP lossless is ~26% smaller than PNG on average but has slightly slower encoding. For photographs, lossless formats are much larger than lossy alternatives — a JPEG photograph at quality 85 is typically 3–10× smaller than the same image in lossless PNG — so lossless is rarely used for photographic web delivery.
Lossless Compression Tools on PicsSizer
Frequently Asked Questions
Does lossless compression reduce image quality?▾
No. Lossless compression preserves every pixel value exactly — image quality is identical to the uncompressed original. The trade-off is larger file sizes compared to lossy compression at equivalent visual quality.
Can I compress a PNG further without quality loss?▾
Yes, using better lossless encoders (Zopfli, pngquant for palette images) or more aggressive DEFLATE settings. PicsSizer's PNG Compressor applies lossless optimizations that typically reduce PNG size by 20–50% without any quality change.